MXPA98007160A - Bags packaged with nanofibers that have improved flu flow characteristics - Google Patents

Abstract

present invention relates to: general area of this invention relates to porous materials manufactured from non-nanofiber packed beds. More specifically, invention relates to altering porosity or packing structure of a packed bed structure with nanofibers, by mixing nanofibers with materials in scaffolding particles having larger dimensions. For example, by adding large diameter fibers to a bed packed with a nanotube, to serve as a scaffold to hold apart smaller nanofibers and prevent nanofiber bed structure from collapsing. This increases average pore size of dough, changing pore size distribution and alters packing structure of packed bed. increase in average pore size is caused by creation of larger channels which improves flow of liquids or gases through e materials

Description

"BAGS PACKAGED WITH NANOFIBRAS THAT HAVE IMPROVED CHARACTERISTICS OF FLUID OF FLUID" BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The invention relates extensively to packed beds with nanofibers having improved fluid flow characteristics with the methods for making the same and methods for using them. More specifically, the invention relates to nanofibers that are uniformly or non-uniformly mixed with support scaffold particulate materials to form packed beds having improved fluid flow regimes and an increased total average pore size. Still more specifically, the invention relates to using these packed beds for a variety of purposes including through flow electrode products, chromatographic media, adsorbent media and filters.

DESCRIPTION OF THE RELATED TECHNIQUE Nanofibre mats and assemblies have been previously produced to take advantage of the increased surface area per gram achieved by using fibers of extremely thin diameter. These prior mats or assemblies are either in the form of tightly dense masses of interlaced fibers and / or are limited to microscopic structures (i.e., having a larger dimension of less than 1 micron). The nanofiber mats or mounts have been prepared previously by dispersing the nanofibers in aqueous or organic media and then filtering the nanofibers to form a mat. The mats have also been prepared by forming a gel or paste of carbon fibrils in a fluid e.g. an organic solvent such as propanc and then heating the gel or the paste to a temperature above the critical temperature of the medium, removing the supercritical fluid and finally removing the mat or porous plug resulting from the container in which it has been carried out. process. See, US Patent Application Number 08 / 428,496 entitled "Three-Dimensional Macroscopic Asseblages of Randomly Oriented Carbon Fibrils and Composites Containing Same" by Tennent et al., Which is incorporated herein by reference. One of the disadvantages of prior assemblies or mats manufactured by the methods described above is the poor characteristics of fluid flow within the structure. As the suspensions of nanofibers become drained of the suspension fluid, in particular water, the surface tension of the liquid tends to pull the nanofibers towards a dense packed "mat". Alternatively, the structure can simply be crushed. The pore size of the resulting mat is determined by the spaces between the fibers which, as a result of the compression of these mats, tend to be quite small. As a result, the fluid flow characteristics of these mats are deficient. Therefore, even though previous work has shown that nanofibers can be assembled into thin packed membrane assemblies through which the fluid will pass, the small diameters of the nanofibers result in a very small pore structure that imposes large resistance to fluid flow. It would be desirable to overcome the aforementioned disadvantages by producing a porous packed bed having improved fluid flow and an altered pore size distribution, since there are applications for beds packed with porous nanofibers that require fluid passage and resistance to fluid transport It creates serious limitations and / or inconveniences for these applications. The improved fluid flow characteristics obtained by this invention make these applications more feasible and / or more efficient.

OBJECTS OF THE INVENTION Therefore, an object of this invention is to provide bed structures packed with porous nanofibers that have improved fluid flow characteristics and / or a pore size. average increased. Another object of the invention is to provide a composition of matter comprising a packed bed with three-dimensional macroscopic nanofibers consisting of a mixture of randomly oriented nanofibers and larger scaffolding materials. A further object of the invention is to provide processes for the preparation of and methods of using beds packed with nanofibers having improved fluid flow characteristics. Still a further object of the invention is to provide improved filter means, chromatographic media, absorbent media, electrodes, EMI protectors and other industrial value compositions, based on the porous packed beds of three-dimensional nanofibers.

The objects and advantages of the invention above and others will be pointed out in or will be apparent from the following description and drawings.

COMPENDIUM OF THE INVENTION The general area of this invention relates to porous materials manufactured from beds packed with nanofibers. More particularly, the invention relates to altering the porosity or packaging structure of the packed bed structure with nanofibers by mixing the nanofibers with scaffold particle materials having larger dimensions. For example, adding the large diameter fibers to a bed packed with a nanotube to serve as a scaffold to hold apart the smaller nanofibers and prevent the bed structure of nanofibers from collapsing. This increases the average pore size of the dough by changing the pore size distribution and alters the packing structure of the packed bed. The increase in the average pore size is caused by the creation of larger channels, which improves the flow of liquids or gases through these materials. Accordingly, the object of the invention is to alter the average pore size and packing structure of the packed nanofiber layers, by mixing the larger non-particulate material preferably fibers having larger diameters. Larger particulate materials alter the packing of nanofibers and lead to structures with reduced resistance to fluid flow. The present invention provides the unexpected advantage of being able to form a packed bed structure of nanofibers with improved fluid flow characteristics, as a result of the scaffolding effect that is provided by the scaffold particulate materials.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a photomicrograph (50,000 fold amplification) of a bed packed with nanofibers, illustrating a mat region of nanofibers comprising randomly oriented interlaced fibrils of carbon. Figure 2 is a photomicrograph (2,000-fold magnification) illustrating a packed bed comprising scaffold fiber particulates and continuous ribbon-like structures of interlaced randomly oriented carbon fibrils.

Figure 3 is a photomicrograph (200-fold amplification) illustrating scaffold particulate materials in the form of fibers (4 to 8 micrometers in diameter) and regions resembling continuous strips of fibril mats. Figure 4 is a photomicrograph (100 times amplification) of a packed bed structure in accordance with the present invention. Figure 5 illustrates a graphical representation of the flow rate / mat structure ratio for comparison nanofiber mats (without scaffolding) where the vertical axis represents the flow regime and the horizontal axis represents the flow of the total volume through of the mat for mats with different thicknesses and densities. Figure 6 illustrates a graphical representation of the flow rate / density ratio of mat comparison carbon nanofiber mats (without scaffolding) where the vertical axis represents the normalized flow rate for the thickness of the mat, and the horizontal axis represents the density of the mat. Figure 7 illustrates a graphical representation of the flow rate / nanofiber fraction ratio of one embodiment of the invention, wherein the vertical axis represents the flow rate and the horizontal axis represents the fraction of nanofibers by weight in a bed of packaging containing carbon fibrils and carbon fibers. Figure 8 is a graphical representation of the current-voltage duration for the electrode of the example 8, where the vertical axis represents the current and the horizontal axis represents the potential applied to different potential exploration regimes.

DETAILED DESCRIPTION OF THE INVENTION DEFINITIONS The term "fluid flow rate characteristic" refers to the ability of a fluid or gas to pass through a solid structure. For example, the rate at which a volume of a fluid or gas passes through a three-dimensional structure having a specific cross-sectional area and a specific thickness or height (ie, milliliters per minute per square centimeter per 25.4 micrometer thickness). ) at a fixed pressure differential through the structure. The term "isotropic" means that all measurements of a physical property within a plane or volume of the packed bed regardless of the direction of measurement, giving a constant value. It will be understood that the measurements of these non-solid compositions should be taken in a representative sample of the packed bed so that the average value of the hollow spaces is taken into account. The term "macroscopic" refers to structures that have at least two dimensions greater than one millimeter. The term "nanofiber" refers to elongated structures having a cross section (angular fibers having edges) or diameter (rounded) less than 1 micron. The structure can be either hollow or solid. This term is further defined below. The term "packed bed", "assembly" or "mat" refers to a structure comprising a configuration of a mass of interlinked individual nanofibers, scaffold fibers and / or scaffold particles. The term "packed bed" will be interpreted below as including interchangeability with the terms "mats," "assemblies," and related three-dimensional structures. The term "packed bed" does not include loose masses of particulate matter. The term "packaging structure" refers to the internal structure of a packed bed including the relative orientation of the fibers, the diversity of and the total average of the orientations of the fiber, the proximity of the fibers to each other, the hollow space pores created by the interstice and the spaces between the fibers and the size, shape, number and orientation of the flow channels or paths that are formed by connecting the hollow space or pores. The term "relative orientation" refers to the orientation of an individual fiber with respect to the others (ie, aligned versus non-aligned). The "diversity of" and "total average" of the fiber orientations refers to the scale of fiber orientations within the packed bed (alignment and orientation with respect to the external surface of the bed). The term "physical property" means an inherent measurable property of the porous packed bed, e.g. resistivity, fluid flow characteristics, density, porosity, etc. The term "relatively" means that 95 percent of the values of the physical property when measured along an axis of or within a plane or within a volume of the structure, as the case may be, will remain within. about 50 percent of a mean value. The term "scaffold particulate material" refers to an appropriate particulate material to provide a scaffold effect when mixed with the nanofibers. At least one dimension of the "scaffold particulate material" is considerably larger than at least one dimension of the nanofibers. The "scaffold particle materials" can have three-dimensional shapes, including fibers, cubes, platelets, disks, etc. The "scaffold particulate materials" are discussed further below. The term "essentially" means that ninety-five percent of the values of the physical property when measured along an axis of or within a plane of or within a volume of the structure, as the case may be , it will stay within plus or minus ten percent of a mean value. The terms "essentially isotropic" or "relatively isotropic" correspond to the scales of variability in the values of a physical property indicated above.

NANOFIBRAS The term nanofibras refers to different fibers that have very small diameters including fibrilLas, very fine filaments, nanotubes, small tubes, etc. These structures provide significant surface area when incorporated into a packed bed structure due to their size. In addition, this structure can be manufactured with high purity and uniformity. Preferably, the nanofiber used in the present invention has a diameter of less than about 1 micron, preferably less than about 0.5 micron and even more preferably less than 0.1 micron and especially preferably less than 0.05 micron. The fibrils, small tubes, nanotubes and very fine filaments referred to in this application can be distinguished from continuous carbon fibers commercially obtainable as reinforcing materials. In contrast to nanofibers, which have desirably large but inevitably finite elongations, the continuous carbon fibers have elongations (L / D) of at least 104, often 106 or more. The diameter of the continuous fibers is also much larger than that of the fibrils, always being > 1.0 micrometer and typically 5 to 7 micrometers. Continuous carbon fibers are manufactured by pyrolysis of the organic precursor fibers, usually rayon, polyacrylonitrile (PAN) and pitch. In this way they can include heteroatoms within their structure. The graphite nature of the "as manufactured" continuous carbon fibers varies, but may be subjected to a subsequent graphitization step. The differences in the degree of graphitization, orientation and crystallinity of the graphite planes, if present, the potential presence of the heteroatoms and even the absolute difference in the diameter of the substrate make the experience with the continuous fibers poor predictive materials. of the chemistry of nanofiber. The various types of nanofibers suitable for use in porous packed bed structures will be discussed below. Carbon fibrils are vermicular carbon deposits having diameters less than 1.0 micrometer, preferably less than 0.5 micrometer, even more preferably less than 0.2 micrometer and especially preferably less than 0.05 micrometer. They exist in a variety of forms and have been prepared through the catalytic decomposition of the various gases containing carbon on the metal surfaces. These vermicular carbon deposits have been observed almost since the advent of electron microscopy. A good early review and reference is found in the article by Baker and Harris, Chemestry and Physics of Coal, Walker and Thrower editors, volume 14, 1978, page. 83 and by N. Rodríguez, J. Mater. Research, volume 8, page 3233 (1993), each of which is incorporated herein by reference. (See also A. Obelin and M. Endo, J. of Crystal Growth, volume 32 (1976), pages 335-349, which is incorporated herein by reference). U.S. Patent No. 4,663,230 issued to Tennent, which is incorporated herein by reference, discloses carbon fibrils that are free of a continuous thermal carbon overcoat and have multiple ordered graphitic outer layers that remain essentially parallel to the fibril axis. As such, they can be characterized as having their axes c, the axes that remain perpendicular to the tangents of the curved graphite layers, essentially perpendicular to their cylindrical axes. In general, they have diameters no greater than 0.1 micrometer and length to diameter ratios of at least 5. Desirably they are essentially free of an overcoat of continuous thermal carbon, ie, pyrolytically deposited carbon resulting from the thermofraction of the gas feed. used to prepare them. The Tennent invention provided access to smaller diameter fibrils, typically from 35 to 700 A units (0.0035 to 0.070 micrometer) and to an ordered graphite surface "as it grew". The fibril carbons of less than the perfect structure, but also without an outer pyrolytic carbon layer have also been grown. U.S. Patent No. 5,171,560 issued to Tennent et al., Which is incorporated herein by reference, discloses carbon fibrils free from thermal overcoating and having graphitic layers essentially parallel to the fibril shafts such that the projection of these layers in the axes of the fibrils extend through a distance of at least two fibril diameters. Typically these fibrils are essentially cylindrical graphitic nanotubes of essentially constant diameter and comprise cylindrical graphite sheets whose axes c are essentially perpendicular to their cylindrical axis. They are essentially free of pyrolytically deposited carbon, have a diameter less than 0.1 micrometer and a length to diameter ratio greater than 5. These fibrils are of primary interest in the invention. Additional details related to the formation of carbon fibril aggregates can be found in the disclosure of US Pat. No. 5,165,909 issued to Tennent; the application of US Patent of Snyder et al. Number 149,573, filed January 28, 1988, and the PCT Application Number US89 / 00322, filed on January 28, 1989 ("Carbon Fibers") WO 89/07163 and the North American Patent Application of Moy and other Serial Number 413,837, filed September 28, 1989 and PCT Application Number US90 / 05498, filed September 27, 1990. ("Fibrilla Aggregates and Method for Manufacturing Themselves") WO 91/05089, and US Application No. 08 / 479,864 issued to Mandeville et al., Filed June 7, 1995 and US Application No. 08 / 329,774 by Bening and others, filed on October 27, 1984 and the North American Application Number 08 / 284,917, filed on August 2, 1994 and the North American Application Number 07 / 320,564, filed on October 11, 1994 by Moy and others, all of which have been assigned to the same concessionaire as the present invention and which are incorporated herein by reference. Moy et al., In the North American Application SN 07 / 887,307, filed May 22, 1992, incorporated herein by reference, describes fibrils prepared as aggregates having different morphologies (as determined by scanning electron microscopy) where they are randomly entangled with one another to form entangled balls of fibrils that resemble bird nests ("BN"); or as aggregates consisting of bunches of straight or slightly bent carbon fibrils having essentially the same relative orientation and having the appearance of combed yarn ("CY") e.g. the longitudinal axis of each fibril in spite of the individual folds (it extends in the same direction as that of the surrounding fibrils in the bundles) or as aggregates consisting of straight or slightly bent fibrils that become loosely entangled with one another to form an "open network" structure ("ON") In open network structures, the degree of entanglement of fibrils is greater than that observed in combed yarn aggregates (where individual fibrils essentially have the same relative orientation) but smaller than that of bird nests, the CY and ON aggregates are more easily dispersed than BN, making them useful in the manufacture of a compound where uniform properties are desired throughout the structure. The fibril axis extends through a distance of less than two fibril diameters, the carbon planes of the graphite nanofiber in section In cross section they adopt the appearance of herringbone. These are called fishbone fibrils. Geus, in U.S. Patent No. 4,855,091 which is incorporated herein by reference, provides a process for the preparation of fishbone fibrils essentially free of a pyrolytic overcoat. - lí these fibrils are also useful in the practice of the invention. McCarthy et al., In U.S. Patent Application Serial Number 351,967, filed May 15, 1989, incorporated herein by reference, discloses processes for oxidizing the surface of carbon fibrils that include contacting fibrils with an oxidizing agent including sulfuric acid (H2SO4) and potassium chlorate (KCIO3) under reaction conditions (eg time, temperature and pressure) sufficient to oxidize the surface of the fibril. The fibrils oxidized according to the McCarthy et al. Processes are oxidized in a non-uniform manner, that is, the carbon atoms are replaced with a mixture of carboxyl, aldehyde, ketone, phenolic groups and other carbonyl groups. The fibrils have also been oxidized non-uniformly by treatment with nitric acid. International Application Number PCT / US94 / 10168 discloses the formation of oxidized fibrils that contain a mixture of functional groups. In a published paper, McCarthy and Bening (Polymer Preprints ACS Div. Of Polymer Chem. 30 (1) 420 (1990)), derivatives of oxidized fibrils were prepared in order to demonstrate that the surface consisted of a variety of oxidized groups. The compounds they prepared, phenylhydrazones, haloaromatic esters, salts, etc. they were selected because of their analytical usefulness for example making bright colors or exhibiting some other intense signal easily identified and differentiated. These compounds were not isolated and unlike the derivatives described herein, they are not of practical importance. The carbon nanotubes of morphology similar to the catalytically grown fibrils described above have been grown in a high temperature carbon arc (Iijima, Nature 354 56 1991, which is incorporated in the present pro reference). It is now generally accepted (Weaver, Science 265 1994, which is incorporated herein by reference) that these arc-grown nanofibers have the same morphology as Tennent's earlier catalytically grown fibrils. Carbon nanofibers grown by arc are also useful in the invention.

SCAFFOLD PARTICLE MATERIALS Scaffold particulate materials are particularly solid, having an appropriate shape and size to provide a scaffold effect when mixed with nanofibers. The scaffold particles are shaped and sized in such a way that they break the packaging structure of the nanofibers. This results in a packed bed having an increased average pore size. The scaffolding shape increases the number of large pores and the average pore size which in turn increases the flow regime of the bed. Scaffold particulate materials are used as a diluent and / or as a mechanically stronger scaffold that helps overcome the forces of surface tension during the drying process that reduces the density of the nanofiber fraction of the "mat" resulting composite. Preferably, the scaffold particle materials have at least one dimension larger than the largest dimension of the nanofibers and / or at least one second larger dimension that is larger than the second largest dimension of the nanofiber. The largest dimension of the scaffold particle can be comparable to the larger dimension of the nanofiber. For example, nanofibers and fat fibers of the same length can be used as long as the diameters of the fat fibers are significantly larger than the diameters of the nanofibers. Preferably, the largest dimension of the scaffold particle material is at least ten times larger than the largest dimension of the nanofibers, more preferably 50 times larger and even more preferably 100 times larger and especially preferred. 200 times higher Preferably, the second largest dimension of the scaffold material is at least 10 times larger than the second largest dimension of the nanofibers, more preferably 50 times larger, even more preferably 100 times larger and especially preferred 200 times greater The scaffold particulate materials preferably also have a larger dimension (eg length for a fiber) greater than 1 micron, more preferably greater than 5 microns, even more preferred greater than 10 microns and especially preferred greater than 50 microns. microns. The scaffold particulate materials preferably have a second larger dimension (eg diameter for a fiber or thickness for a disk) greater than 0.1 micron, more preferably greater than 1 micron and still preferably greater than 3 microns and so especially preferred greater than 5 microns. The shape of the scaffold particles can take many forms as long as the particulate material provides sufficient scaffolding effect to improve the flow characteristics of the fluid by the desired amount. Suitable configurations include fibers, platelets, disks, cones, pyramids, cubes, solid and regular particulate materials, etc. Preferably, the scaffold particulate material has a fiber configuration. The diameter of the fiber in scaffold particles is preferably at least 10 times greater than the diameter of the nanofiber, more preferably 50 times larger and even more preferably 100 times larger and more preferably 200 times larger. The chemistry of the surface, structure or composition of the scaffolding material can also be modified to improve or adjust the scaffolding effect. For example, particulate materials having harsh surfaces can result in increased scaffolding since these particulate materials would be able to keep nanofibers separated better. In accordance with one embodiment of the invention, more than one type of scaffold particle material is incorporated into the packed bed. Scaffold particle materials for example may be polymeric, inorganic, glass or metallic. The particulate material may have a composition equal to or different from the nanofiber. Preferably, the scaffold particulate materials are either glass fiber particles or carbon fibers.

According to a preferred embodiment, the carbon fibers are used in as the scaffold particulate material. Carbon fibers offer the advantage for this purpose of being conductive. Metal fibers, with even higher conductivity, can also be mixed for the same purpose. Accordingly, carbon fibers that are conductive but also made of carbon can be used as the scaffold materials and mixed with the carbon nanofibers to result in a carbon-based packed bed having improved conductivity, flow of improved fluid and high carbon purity.

PACKED BEDS OF NANOFIBERS WHICH HAVE IMPROVED FLUX FLUX The general area of this invention relates to porous packed bed materials manufactured from packaged nanofibers. The invention relates to a method for altering the porosity of a packed bed structure which is made by mixing the nanofibers with one another, with larger diameter fibers or the particulate materials to serve as a scaffold in order to retain the separated ones. smaller nanofibers and prevent them from collapsing. The creation of larger channels within these composite materials improves the flow of liquids or gases through these materials. The flow of a fluid through a capillary is described by the Poiseuille equation that is related to the flow regime at the pressure differential, the viscosity of the fluid, the length of the trajectory and the size of the capillaries. The flow regime per unit area varies with the square of the pore size. Consequently, a pore twice as large results in four times larger flow regimes. The creation of pores of a considerably larger size in the structure of the bed packed with nanofibers results in an increased fluid flow because the flow is considerably greater through the larger pores. As noted above, packed beds of nanofibers not provided with a scaffolding mechanism result in deficient fluid flow characteristics. This is particularly the case when the liquid suspensions of the nanofibers are drained or discharged from the suspension fluid and the surface tension of the liquid tends to pull the nanofibers towards a dense packed "mat" with the pore size determined by the spaces between the fibers. that tend to be quite small. This results in a packed bed having poor fluid flow characteristics. When packed beds of nanofibers are formed without the scaffolding materials, they crush and form dense mats. The scaffold particles retain the mats and break these mats separating them forming regions of discontinuous nanofibers and gap channels between these regions. Referring to Figure 1, the photomicrograph illustrates the dense packing of the nanofibers within the mat region of nanofibers or domain. Figure 2 is a lower amplification microphotograph illustrating the nanofiber domains adhered to and forming "tape-like" continuous structures between and in the scaffold particulate materials. The interwoven fibrous structures of nanofibers cause them to adhere together to form a structure similar to a continuous or felt-like ribbon instead of separating completely into discrete particles. If non-fibrous nano particles (for example, spheres) are used, these particles would simply fall through the structure and separate to the bottom. Figures 3 and 4 are microphotographs of lower amplification of the packages containing carbon fibrils and carbon fibers.

Surprisingly, the packed beds comprise larger scaffold particles mixed together with the nanofibers offer improved flow characteristics. This allows the raised surface area of the nanofibers to be used more easily in situations where the transport of bulk fluid or gas through the material is needed. The improved packing structure of the packed bed provides large flow channels that allow a large surface area of nanofibers to be accessible. That is to say, the nanofibers that line the outer walls or that are in contact with the large flow channels formed within the composite structure, allow an increased amount of surface area of accessible nanofibers. One aspect of the invention relates to a composition of matter comprising a porous packed bed having a plurality of nanofibers and a number of scaffold-mixed materials to form a porous structure. Preferably, the packed bed has an improved fluid flow characteristic. Preferably, the fluid flow rate water is greater than 0.5 milliliter per minute per square centimeter, at a pressure differential across the packed bed of about one atmosphere for a bed having a thickness of 25.4 microns, more preferably greater than 1.0 milliliter per minute per square centimeter. Broadly, the invention is a composition of matter consisting essentially of a three-dimensional macroscopic assembly of a multiplicity of randomly oriented nanofibers, mixed with scaffold particulate materials. Preferably, the beds have at least two dimensions greater than one millimeter, more preferably greater than 5 millimeters. Preferably, the resulting packed beds have a bulk density of 0.1 to 0.5 gram per cubic centimeter. The packed bed manufactured according to the invention has structural and mechanical integrity, that is, the beds can be handled without breaking or separating even when the beds can be somewhat flexible. The packed beds have a felt-like character, as a result of the nanofibers intertwining together to form a structure as if woven randomly. The packed beds have significantly higher strengths and tenacity compared to simple loose particle masses. Preferably, the packed bed of the invention has at least one fluid flow characteristic that is greater than that of the packed bed of nanofibers without the scaffold particulate materials. That is, the addition of the scaffold particulate materials improves the fluid flow rate, for example as compared to a packed bed of nanofibers without the scaffolding particulate materials. Preferably, the addition of the scaffold increases the flow rate by a factor of at least two, more preferably by a factor of at least five, even more preferably by a factor of at least ten and especially preferred by a factor of at least 50. According to a preferred embodiment, the packed bed has a surface area greater than about 25 square meters per gram. Preferably the packed bed has relative or essentially uniform physical properties together with at least one dimensional axis and desirably has relatively or substantially uniform physical properties in one or more planes within the packed bed, i.e., they have isotropic physical properties in that plane. In other embodiments, the entire packed bed is relative or essentially isotropic with respect to one or more of its physical properties. Preferably, the packed bed has essentially isotropic physical properties in at least two dimensions. When figures or platelets are used as scaffold materials, they tend to be aligned in a single plane. However, the resulting structure is isotropic in the plane of alignment. The packed bed may have a uniform or non-uniform distribution of the scaffold particles and nanofibers. In accordance with one embodiment of the invention, the distribution of scaffold particle materials within the packed bed of nanofibers is non-uniform. As can be seen when comparing Figures 1, 2, 3 and 4, even when the distribution can have uniform appearance at lower amplifications, the major amplifications indicate that the nanofibers can congregate and form domains similar to continuous tape. Although this may occur, the macroscopic properties of the material may be relatively uniform as shown in Figure 4. Alternatively, the packaged structure may be non-uniform. For example, a thin layer region having a higher concentration of nanotubes can be formed in the upper portion of packed bed. Alternatively, the thin layer of nanofibers can be formed in the lower portion or within the packed bed structure. The distribution of materials in scaffolding particles can be varied to alter the properties of the packed bed.

The average pore size and the packed packing structure of the packed bed can be adjusted by varying several parameters. These parameters include: (a) the weight percentage of the nanofiber and / or the support particle material, (b) the size, configuration and surface characteristics of the nanofiber and / or the scaffold material, (c) ) the composition of the nanofiber and / or scaffold material (eg, carbon versus metal), and (d) the method for manufacturing the packed bed. Even though the interstices between the nanofibers are irregular in both size and configuration, they can be believed to be pores and characterized by the methods used to characterize the porous media. The size distribution of the interstices and the hollow spaces within these networks can be controlled by concentration at the dispersion level of the nanofibers mixed with the scaffold support materials. The addition of scaffolds for the nanofiber packaging causes an alteration of the pore size distribution. Even though the pore size within the domain of the nanofiber mat is not significantly altered, the separation of these domains results in larger gap channels between the nanofiber domains. The result is a bimodal pore size distribution.

The small pore spaces with the nanofiber domains and a large gap space between these domains. According to one embodiment, the porous packed beds can contain a quantity of nanofibers ranging from 1 percent to 99 percent by weight, preferably from 1 percent to 95 percent by weight, even more preferably 1 percent by weight at 50 weight percent, particularly preferably from 5 weight percent to 50 weight percent. The corresponding amount of the scaffold material varies from 99 percent to 1 percent, more preferably from 99 percent to 5 percent by weight, even more preferably from 99 percent to 50 percent by weight and from especially preferred from 95 weight percent to 50 weight percent. According to another embodiment, the porous packed beds can comprise a non-hollow solid volume having an amount of nanofibers ranging from 1 volume percent to 99 volume percent, preferably from 1 volume percent to 95 percent. in volume, even more preferably from 1 volume percent to 50 volume percent, especially preferably from 5 volume percent to 50 volume percent. The corresponding amount of the scaffold particulate material ranges from 99 percent to 1 volume percent (volume of solid without voids), more preferably from 99 percent to 5 volume percent, even more preferably 99 percent at 50 percent by volume and especially preferably from 95 percent to 50 percent by volume. As discussed above, by varying the amount of the nanofiber and the material in scaffold particles the packing structure is varied so the fluid flow characteristics are varied. Figure 5 is a graphical representation of the relationship between water fluid flow and mat thickness for a carbon fibril mat (2 square centimeters) without scaffolding particulate materials. Figure 6 illustrates a graphical representation of the flow rate versus mat density. As you can see from the graph, the fluid flow characteristics for these mats are efficient. The flow rate decreases exponentially as the density of the mat increases, corresponding to a decrease in the pore volume. Figure 7 is a graphical representation of the relationship of the fluid flow rate / nanofiber fraction for a packed bed (2 square centimeters) manufactured in accordance with the present invention. As can be seen from the graph, the increased flow rates are achieved by adding scaffold fibers to a mat of nanofibers.

According to a preferred embodiment of the invention, the nonanofibers have an average diameter less than 0.1 micron and the maerials in scaffold particles have a first dimension greater than about 1 micron and a second dimension greater than about 0.5 micron. According to one embodiment of the invention, the packed bed further comprises an additive (eg a particulate additive) as a third component that is incorporated into the bed in an amount ranging from 0.01 weight percent to 50 weight percent , more preferably from 0.1 percent to 20 percent by weight, even more preferred from 0.01 percent to 10 percent by weight and especially preferably from 0.01 percent to 5 percent by weight.

Methods for Fabricating Packed Beds with Nanofibers Generally, the method involves mixing the nanofibers with the scaffolding materials to form a packed bed structure. The appropriate comparable methods disclosed in the application of the United States Number 08 / 428,496 filed on 27 April 1995, are incorporated herein by reference. In accordance with one embodiment of the invention, a porous composite packed bed having a plurality of nanofibers and a number of scaffold particulate materials is prepared by a method comprising the steps of: (a) dispersing the nanofibers and the scaffold particulate materials in a medium to form a suspension; and (b) separating the medium from the suspension to form the packed bed. In accordance with a preferred embodiment of the invention, the packed beds were formed using either commercial glass fiber glass fibers (eg, Whatman® GF / B glass fiber filter paper) or crushed carbon fibers as the materials in scaffolding particles. In both cases, the nanofibers (graphite fibrils) and the larger fibers were mixed together to form suspensions of the two and filtered in vacuum filter collectors to remove the fluid and form a "mat" or dry packed bed. The medium of preference is selected from the group consisting of water and organic solvents. The separation step may comprise and filter the suspension or evaporate the medium from the suspension. According to one embodiment, the suspension is a gel or paste comprising the nanofibers and the scaffold particles in a fluid. The separation step may comprise the steps of: (a) heating the gel or paste in a pressure vessel to a temperature greater than the critical temperature of the fluid; (b) removing the supercritical fluid from the pressure vessel; and (c) removing the packed porous composite bed from the pressure vessel In accordance with another embodiment, a slurry of carbon nanotubes is prepared and the ground or crushed segments of the particulate support materials are added to a suspension containing the Nanofibers are agitated to keep the materials dispersed.The media is subsequently separated from the suspension forming a packed bed that has good fluid flow characteristics.The support fiber particulate materials of length of 3.18 millimeters and even smaller, work all right.

Methods for Using the Nanotube-packed Beds The beds packed with fibril can be used for purposes for which porous media are known to be useful. These include filtration, electrodes, adsorbents, chromatography media, etc. In addition, the packed beds are a convenient volumetric form of nanofibers and can therefore be used for any of the known applications including especially EMI protection, polymer composites, active electrodes, etc. For some applications such as EMI protection, filtration and current collection, unmodified nanofiber packed beds can be used. For other applications, the nanofiber packed beds are a component of a more complicated material, that is, they are part of a compound. Examples of these compounds are polymer molding compounds, chromatography means, electrodes for fuel cells and batteries and ceramic compounds, including bioceramics such as artificial bone. In some of these compounds, as well as molding compounds and artificial bone, it is desirable that non-nanofiber components fill - or essentially fill - the porosity of the packed bed. For others, such as electrodes and chromatography media, their utility depends on the compound that retains at least a certain amount of the porosity of the packed bed. Rigid networks can also serve as the basic structure in biomimetic systems for molecular recognition. These systems have been described in U.S. Patent Number 5,110,833 and in International Patent Publication Number W093 / 19844. The packed bed products described above can be incorporated into a matrix. Accordingly, a non-nanofiber component is filtered through the bed and solidified to form a compound. Preferably, the matrix is an organic polymer (e.g., a thermosetting resin such as epoxide, bismaleimide, polyamide, or polyester resin).; a thermoplastic ream; a resin molded by reaction injection; or an elastomer such as natural rubber, styrene and butadiene rubber, or cis-1, -polybutadiene); an inorganic polymer (e.g., a polymeric inorganic oxide such as glass), a metal (e.g., lead or copper), or a ceramic material (e.g., Portland cement).

Packed Beds as Electrodes In accordance with a preferred embodiment, the packed beds described above are used as they have been shown to be good porous electrode materials. Accordingly, another aspect of the invention relates to through-flow electrode materials comprising packed beds of nanofibers having improved fluid flow characteristics. The porous electrode material is manufactured from packed bed mixtures of nanofibers and scaffold particulate materials. The electrode materials take advantage of the composite properties of the different materials in the composite mixture. In addition, the conductivity of the assembly can be increased when different materials in conductive scaffold particles are mixed with the nanofibers. According to a modality mode, the electrodes can be manufactured by fixing a conductive wire to the sections of the beds packed with conductive epoxy. These electodes can be examined by cyclic voltiamperimetry. It was observed that the material leaked better than when the fibrils were alone. In accordance with another embodiment, an electrical contact is formed by forming the packed bed on a conductive surface. For example, the packed bed can be formed by filtering the packed bed in a conductive mesh. Preferably, a mesh or screen of gold, platinum, nickel or stainless steel is used. In addition, the conductivity can be limited by the internal connection of the nanofibers. Compounds that have larger fibers mixed with the nanofibers offer improved porosity and / or flow characteristics as well as conductivity. This allows the surface area of the nanofibers to be used more easily in electrode applications in situations where both the conductivity and the flow of fluid through the material are necessary. The addition of different amounts of materials in larger scaffolding particles with a fixed amount of nanofibers allows the internal volume to be "tuned" finer. The small pore sizes within the structure result in a thin film electrochemical behavior and the effective "thickness" of the effect of the film layer can be varied. Therefore, highly porous conductive electrodes can be manufactured with different effective void volumes.

EXAMPLES The following examples are illustrative of some of the products and methods for making same that are within the scope of the present invention. Of course, they should not be considered as limiting the invention in any way. Numerous changes and modifications may be made with respect to the invention.

Example I (Comparison) Preparation of Fibrilla Mats Using Prior Methods A dilute dispersion of fibrils is used to prepare the porous mats or sheets. A fibril suspension containing 0.5 percent fibrils in water is prepared using a Waring blender. After subsequent dilution up to 0.1 percent, the fibrils are further dispersed with a probe-type sonicizer. The dispersion is then filtered under vacuum to form a mat, which is then dried in the oven. The mat has a thickness of approximately 0.20 millimeter and a density of approximately 0.20 gram per cubic centimeter corresponding to a pore volume of 0.90. The electrical resistivity in the plane of the mat is approximately 0.02 ohm per centimeter. The resistivity in the direction perpendicular to the mat is approximately 1.0 ohm per centimeter. The fluid flow characteristics of the mat are deficient.

Example II (Comparison) Preparation of Fiber Mats Using Methods Previous A suspension of fibrils containing 0.5 percent fibrils in ethanol is prepared using a Waring Blender. After subsequent dilution up to 0.1 percent, the fibrils are further dispersed with a probe-type sonicizer. The ethanol is then allowed to evaporate and the mat is formed. The fluid flow characteristics of the mat are deficient.

Example III (Comparison) Preparation of Porous Fiber Corks Using the Previous Methods The removal of supercritical fluid from a well dispersed fibril paste is used to prepare low density configurations. 50 cubic centimeters of a 0.5 percent dispersion in n-pentane is loaded into a slightly larger capacity pressure vessel that is equipped with a needle valve to allow slow release of pressure. After the vessel is heated to a temperature greater than the critical pentane temperature (Tc = 196.6 ° C), the needle valve is slightly opened to discharge the supercritical pentane through a period of about one hour. The resulting solid fibril plug, which has the configuration of the interior of the container, has a density of 0.005 gram per cubic centimeter corresponding to a fraction of the pore volume of 0.997 percent. The resistivity is isotropic and approximately 20 ohms per centimeter. The mat has deficient fluid flow characteristics.

Example IV (Of the Invention) Preparation of composite fibrous mats and Fiberglass A suspension of fibrils was prepared by mixing 2 grams of fibrils in 400 milliliters of deionized water (0.05 percent, weight / weight) and mixing in a Waring® mixer for 5 minutes at high speed. 60 milliliters of the suspension were diluted in 200 milliliters of deionized water and sonified with a Branson® probe sonator of 450 Watt for 13 minutes at high power with a 100 percent duty cycle to produce a dispersion of fibrils. Drills were drilled (6.35 mm diameter, 6.6 milligrams per disc) of a Whatman® GF / B glass fiber filter. The aliquots of the dispersion of the fibril material and the glass fiber discs were mixed in the proportions indicated in Table 1: TABLE 1: Suspensions Containing Carbon Nanotubes and Fiberglass Particles Water Fiber Suspension Compound Nanotube Glass Number (Deionized Carbon Disc Number) 184-20-1 20 milliliters 0 80 milliliters 184-20-2 20 milliliters 10 80 milliliters 184-20-3 20 milliliters 20 80 milliliters 184-20-4 20 milliliters 30 80 milliliters 184-20-5 20 milliliters 40 80 milliliters Each 100 milliliters of the mixture was sonified for an additional 4 minutes at high power and filtered on a 0.45 micron MSI nylon filter to a Millipore membrane filter collector of 47 millimeters. The fibril / fiberglass composites formed felt-like mats that detached from the nylon membranes and were dried for several hours at 80 ° C between two pieces of filter paper under a weight to maintain the flat shape. The area of each mat disc defined by the dimensions of the filtering collector was 10 square centimeters. Each mat was weighed and the thickness was measured with calibrators. The data is listed in Table 2: TABLE 2: Data of the Fiberglass / Fiberglass CC Mat Mat 80 Weight Area Height Weight (milli- (cpr) (micrometers) glass grams) (milligrams) 184-20-1 35.3 10 139.7 0.0 184-20-2 101.37 10 292.1 66.0 184-20-3 170.75 10 546.0 132.0 184-20-4 292.85 10 889 256.9 184-20-5 554.38 10 3048 518.4 TABLE 2 (CONTINUED) Mat 80 Weight of Glass d "Fibrilla d" Total fibril g / cc g / cc g / cc milligrams 184-20-1 35.3 0.00 0.25 0.25 184-20-2 35.4 0.23 0.12 0.35 184-20-3 38.8 0.24 0.07 0.31 184-20-4 36.0 ** 0.29 0.04 0.33 184-20-5 36.0 ** 0.17 0.01 0.18 * 6.6 milligrams / disc ** graduated to 36 milligrams cubic centimeters in total The glass d "and the Fibrilla d" refer to a total weight of fibril or fiberglass divided by the total volume of the mat.

The flow characteristics of each mat were measured by monitoring the flow of water through each mat in a diameter diaphragm filter manifold 25 millimeter connected with a vacuum pump capable of attracting a vacuum to about 736.60 millimeters of mercury. The 10 square centimeter mats were centered and clamped in the 25 mm diameter filter manifold ensuring that the fluid could flow only through the mat and not around any outer edge. The deionized water used for the flow studies was filtered in sequence through a 0.45 micron pore size nylon filter. A 0.2 micron pore size cellulose membrane filter and finally a 0.1 micron pore size cellulose membrane filter to remove traces of materials that could interfere with flow studies. For each mat, the deposit in the collector was filled above the volume line of 15 millimeters and the vacuum was applied to establish the flow. When the meniscus at the top of the water level crossed the 15-millimeter mark, the operation of a synchronizer was started and the time was recorded as the fluid level up to the lower level marks until the level mark of 5 was reached. milliliters. The active filtration area was approximately 2 square centimeters. In this way the fluid flow was measured at several time points during the passage of 10 milliliters of water. This procedure was followed for each composite mat as well as for a Whatman® GF / B glass fiber filter sheet. The flow data is listed in Table 3: TABLE 3: Measured Times * versus Volumes Flowed for Fiber / Fiberglass Mats Level GF / B 184-20-1 184-20-2 184-20-3 184-20-4 184-20-5 milliliters 35 0.00 0.00 0.00 0.00 0.00 0.00 14 -. 14 - 2.23 3.97 1.02 0.13 - 13 -. 13 - 5.02 8.07 2.47 0.29 0.08 12 -. 12 - 7.53 - 3.57 0.45 - eleven - . 11 - 10.02 - 4.77 0.58 0.17 -. 10 - 12.45 - 5.85 0.72 - 9 - - - 6.87 0.87 0.25 8 -. 8 - - - 7.98 1.00 - 7 -. 7 - - - 8.93 - 0.34 6 -. 6 - 22.45 - 10.00 1.29 - 5 0.03 24.98 34.30 11.02 1.44 0.43"10 indicates that we did not measure * times in minutes For each filter mat the flow versus time was linear indicating that the mats had not been clogged and that the flow rate was constant throughout the elapsed time. It was also observed that the flow rate increases with the increased proportions of glass fibers in the composite mats. As seen from the data in Table 3, the flow regime observed for composite mat number 184-20-5 is almost two orders of magnitude higher than for mat number 184-20-1 a composite fibrillated mat .

Example V (Of the Invention) Preparation of the mats composed of fibrils and carbon fibers. Mats composed of fibrils and ground carbon fibers were prepared and examined to determine the flow properties. A suspension of fibrils was prepared by mixing two grams of fibrils in 400 milliliters of deionized water (0.5 weight percent / weight) and mixing in a Waring® mixer for 5 minutes at high performance. 70 milliliters of the suspension was added to 280 milliliters of deionized water. A magnetic stirring bar was added and the suspension was subjected to 20 minutes of sonification with a 450 Watt Bransonic® probe sonicator with constant stirring to more fully disperse the fibrils and prepare 350 milliliters of a 0.1 percent material dispersion. in weight / weight. The weighed amounts of the crushed carbon fibers (crushed length of 3.18 millimeters, of Renoves fibers, ex-PAN) were placed in a series of beakers (seven) in the proportions shown in Table 4.

TABLE 4 Weight Number of CF Crushed H2O Sample Solution of 3.18 mm Fibers 6 0 mg 100 ml 50 ml 7 50 mg 100 ml 50 ml 8 75 mg 100 ml 50 ml 9 100 mg 100 ml 50 ml 10 125 mg 100 ml 50 ml 11 150 mg 100 ml 50 ml 12 200 mg 100 ml 50 ml 100 milliliters of deionized water and 50 milliliters of the dispersion of the 0.1 percent fibril material were added to each beaker. Each of the seven solutions was sonicated for 5 minutes with agitation and filtered on a 0.45 micron nylon filter in a Millipore membrane filter collector of 47 millimeters. The mats were left in the membranes, placed between pieces of filter paper and dried overnight at 80 ° C between two pieces of filter paper under a weight to maintain the flat shape. The weight and thickness of each mat of 10 square centimeters was measured and the data (after subtracting from the nylon membrane weight of 93.1 milligrams and thickness of 101.6 microns) are shown in Table 5 together with a list of the fractional composition of each of the mats. TABLE 5 6 7 8 9 10 11 12 Weight in mg 52.6 100.4 131.8 157.3 180.6 204.3 248.1 Micrometers 1016 2082.8 2943.2 3657.6 4265.6 5486.4 6705.6 Weight of GF 52.6 53.0 53.0 53.0 53.0 53.0 53.0 Weight of CF 0.0 48.4 78.8 104.3 127.6 151.3 195.1 % of GF 100% 52% 40% 34% 29% 26% 21% % CF 0% 48% 60% 66% 71% 74% 79% d 'GF 0.21 0.10 0.08 0.06 0.05 0.40 0.03 d 'CF 0.00 0.09 0.12 0.12 0.12 0.11 0.12 d Total 0.21 0.20 0.20 0.17 0.18 0.15 0.15 GF = graphic fibrils d' GF = weight of fibrils divided by the total volume of the mat d 'CF = weight of carbon fibers divided by the total volume of the mat The fibril / carbon fiber mats still in the nylon membranes were used for flow studies as described in the previous example and the flow data are shown in Table 6. The flow through the nylon filter of 0.45 micrometer in itself is very high. Correspondingly, their presence does not significantly alter the flow measurements of the supported mats.

TABLE 6 Level 10 11 12 (ml) 0 0 0 0 0 0 0 14 2.0 8.5 8.6 2.0 0.8 0.4 0.2 13 4.1 14.3 16.6 3.9 1.8 0.7 0.5 12 6.1 19.0 24.6 5.6 2.8 1.0 0.7 11 - 22.8 32.1 7.2 3.7 1.3 0.9 -. 10 -. 10 - 26.8 39.2 8.8 4.5 1.6 1.2 9 -. 9 - 30.8 46.2 10.5 5.4 1.9 1.4 8 -. 8 - 35.3 54.0 12.1 6.3 2.3 1.6 7 16.3 39.3 - 13.7 7.2 2.5 1.8 6 -. 6 - 44.2 - 15.2 8.1 2.9 2.1 20.6 48.5 - 16.8 9.0 3.2 2.3 For each filter mat, the flow versus time regime was linear indicating that the filters had not been clogged and that the flow rate was constant over time. It was observed that compared to a simple fibril mat, the flow regime shows a slight decrease with the two lowest concentrations of carbon fiber but rises dramatically to higher carbon fiber levels.

Example VI (Of the Invention) Use of Fiberglass / Fiberglass Composite Mats as Electrodes The pieces of fibril / fiberglass composite mats used in Example IV of approximately 5 mm by 8 mm were cut from the mats with a razor of shaving and modeled in the form of electrodes. The modeling involved connecting a section of copper wire with one end of each section of millimeters by 8 millimeters with graphite paint (Ladd Industries) and isolating the contact tip with epoxy. The copper wire was insulated in a glass sleeve and was sealed with epoxy to the mat section mounted in such a way that only 4 millimeters by 4 millimeters of "flag" of the composite mat remained exposed. Two electrodes of each mat were prepared as indicated in the table. TABLE 7 Compound No. Electrode No. 184-20-1 184-21-1,2 184-20-2 184-21-3,4 184-20-3 184-21-5, 6 184-20-4 184-21-7, 8 184-20-5 184-21-9,10 The composite electrodes were examined by cyclic voltiamperimetry using a potentiostat EG &G PAR 273, a reference electrode Ag / AgCl (Bioanalytical Systems, Inc.) and a Pt thickness counter electrode in a single compartment cell (Bioanalytical Systems, Inc.) filled with a solution containing 3 mM of potassium ferricyanide, 3 mM of potassium ferrocyanide and 0. 5 M of K2SO4 in water. The voltiamperigrames ferri / ferricyanide cyclics exhibited oxidation and reduction waves with characteristics that varied with the composition of the electrodes. The characteristic features of the cyclic voltiamperigrams recorded at an exploration rate of 25 mv / second are listed in Table 8. TABLE 8 Thickness number * micrometers / I ^ mA EPA 'v vs E c v vs Electrode Area ** cm2 Ag / AgCl Ag / AgCl 184-21-1 139.7 / 0.140 0.6 0.275 0.225 184-21-3 292.1 / 0.215 1.2 0.295 0.215 184-21-5 546.1 / 0.187 1.4 0.310 0.21 184-21-7 889 / 0.165 2.7 0.380 0.14 184-21-9 3048 / 0.210 2.7 0.550 -0.02 * Thickness in micrometers ** Area in cm2 In electrode 184-21-1, which consists only of fibrils, it showed very pronounced ridges with minimal ridge to ridge separation consistent with a redox process that takes place inside the porous electrode with very small pores. The shape and separation of the crest between the anodic and cathodic crests were similar to that observed with a thin layer cell. The dependence of the scanning regime on the anodic ridge current shows an almost linear dependence for the electrode 184-21-1, but becomes increasingly non-linear as the prop- ation of glass fibers in the electrode material increases. Anodic peak currents in milliamperes, recorded at different exploration regimes, are shown in Table 9.

TABLE 9: Ridge Anodic Current --A versus Exploration Regime, mv / sec.

Wire Regime Pt 184-20-1 184-20-3 184-21-5 184-21-7 184-21-9 Scan (1 cm x mv / sec 0.05 cm) - . 5 - - - - - 0.975 - - - - 1.4 1.58 -. 25 - 0.625 1.21 1.45 2.8 2.75 50 0.115 1.08 2.13 2.45 4.4 4.15 100 -. 100 - 2.03 3.75 4.15 7 5.9 Example VII (Of the Invention) Use of Composite Fiber / Carbon Fiber Mats as Electrodes The mats composed of fibrils and carbon fibers were used as electrodes. The carbon fibers are electrically conductive. Three fibril / carbon fiber composite mats were prepared using the method described in the aforementioned previous examples. The proportions are shown in Table 10.

TABLE 10: Composition of Fibrilla / Carbon Fiber Mats Used for Electrodes Mat. Compound Electrodes Carbon Fiber Carbon Nanotubes No. Nos. (Mg) (ml of suspension) 184-22-1 184-28-1.2 30 20 184-22-2 184-28-3 60 20 184-22-3 184-28-4.5 120 20 The fibril / carbon fiber mats electrodes were prepared using the method described in Example VI. The dimensions of the electrode are listed in Table 11 below.

TABLE 11 Electrode Area (cm ^) Thickness (micrometer) 184-28-1 0.146 279.4 184-28-2 0.118 279.4 184-28-3 0.182 457.2 184-28-4 0.175 939.8 184-28-5 0.193 939.8 The composite electrodes were examined by cyclic voltiamperimetry using an EG & G potentiostat 273, an Ag / AgCl reference electrode (Bioanalytical Systems, Inc.) and a Pt gauze counter electrode in a single compartment cell (Bioanalytical Systems, Inc.) filled with approximately 15 milliliters of a solution containing 3 mM of potassium ferricyanide, 3 mM potassium ferrocyanide and 0.5 M K2SO4 in water. The ferric / ferrocyanide cyclic voltiamperigrames exhibited oxidation and reduction waves with characteristics that varied with the composition of the electrodes. The characteristic features of cyclic voltiamperigrams are listed in Table 12.

TABLE 12: Summary of the Cyclic Ferrite / Ferrocyanide Voltiamperimetry data in Fibrilla / Carbon Fiber Electrodes Parameter Wire Pt 184-28-1 184-28-3 184-28-4 EPA 0. 32 0. 23 0. 290 0. 3. 4 EPC 0. 15 0. 29 0. 215 0. 17 EP-P 170 60 75 170 IpA at 5 mv / sec, mA - - 0. 69 - IPA at 10 mv / sec. mA - 0.375 1.2 2.9 IPA at 25 mv / sec, mA 0.0663 0.80 2.55 5.3 IPA at 50 mv / sec, mA 0.0875 1.38 4.3 8.2 IPA at 100 mv / sec, mA 0.108 2.38 7.25 12.3 EpA = anodic peak potential at 25 mv / sec, V vs Ag / AgCl EPC = cathodic peak potential at 25 mv / sec, V vs Ag / AgCl Ep_p = separation of peak to peak potential at 25 mv / sec, mv IpA = anodic peak current All three carbon nanotube / carbon fiber composite electrodes showed very intense oxidation and reduction ridges with a peak to peak ridge separation compatible with a redox process that takes place within the porous electrodes that have very small pores. The shape and separation of the crest between the anodic and cathodic ridges is similar to that observed for a thin-layer cell. The dependence of the scanning regime on the anodic peak current shows an almost linear dependence for the electrode 184-28-1, but some deviation from the linear dependence is observed for the electrodes 184-28-3 and 184-28-4 . Each composite mat has the same amount of carbon nanotubes per unit area, but the addition of carbon fibers to the composite results in an increase in thickness and therefore in the volume of the electrode. The peak currents and the integrated currents increase with the electrode volume as expected due to the increased amounts of the ferri / ferrocyanide solution within the porous electrode. These results demonstrate that the porosity of the fibril mat electrodes can be modified through the formation of compounds with larger diameter fibers and allowing access to larger amounts of material in the solution phase. In addition, the use of conductive carbon fibers retains the conductive nature of the fibril mats since the fibrils in the mats are diluted with the largest carbon fibers in the composite. The carbon fibers have a diameter of about 7 to 8 micrometers and the fibrils have a diameter of about 0.01 micrometer. Thus, even though the fibril mat used to make the 184-28-4 electrode contains 80 percent carbon fibers (in weight / weight), the carbon fibers contribute little to the total surface area of the electrode. This is confirmed by measurements of the charge currents of the double layer capacitance that correlate with the electrochemically accessible surface area. Double layer charge currents were measured by recording the cyclic voltiamperigrams at 10 mv / second in an electrolyte containing only 0.5 M K2SO in water. Half of the difference of the total current between the cathode and anodic scans of the cyclic voltiamperigram measured at 0.0 V vs Ag / AgCl was taken as the double layer charge current (Idl). As seen from the data in Table 13, the normalized double layer charge current for the electrode area and therefore the fibril mass, is almost constant even when the carbon fiber content of the materials of the Electrode varies across a wide scale.

TABLE 13 Electrode Idl, mA rea Idl / Area 184-28-1 0.0075 0.146 0.514 184-28-3 0.0085 0.182 0.466 184-28-4 0.100 0.175 0.572 Example VIII (Of the Invention) Use of Fibrilla Mats as Through-Flow Electrodes A suspension of 50 milliliters of carbon nanotubes in water was prepared at a concentration of 1 milligram per milliliter. The suspension was subjected to sonification with a Bronson probe sonder of 450 watts at full power with a 20 percent duty cycle for 20 minutes to ensure that the carbon nanotubes were well dispersed. The dispersion was vacuum filtered to a 0.45 micron MSI nylon filter in a Millipore membrane filter collector of 47 mm. The carbon nanotubes formed a felt-like mat that peeled off the nylon membrane and dried for two hours at 80 ° C between two pieces of filter paper under a weight to maintain flatness. The thickness (or height) of the dried carbon nanotube was 203.20 micrometers with calibrators. A 13 mm arc punch was used to prepare a 13 mm diameter disc of the carbon nanotube mat. An electrochemical flow cell of a 13 mm plastic Swinney membrane filter cutter was constructed by placing a disk of diameter 13 millimeters of gold mesh (400 mesh, Ladd Industries) on the upper part of the membrane support and making electrical contact with the screen with an insulated platinum wire with Teflon® thermal shrink tubing that was fed through the wall of the filter holder for external connection as the working electrode of a three-electrode potentiostat circuit. The gold mesh was fixed in place with a minimum amount of epoxy around the outer edge. A gold strip was molded into a ring and placed in the lower bottom stream section of the filter holder and connected to a platinum wire conductor fed through the wall of the filter holder for external connection as the counter electrode for the three-electrode potentiostat circuit. A ring of 0.5 millimeter diameter of silver wire was electrochemically oxidized in an M of HCl, rinsed with water and placed in the upper section of the filter holder with the end of the wire having been led through the wall for external connection as the reference electrode in the three-electrode potentiostat circuit. The appropriate external contacts in the flow cell were connected to the work, the counter and the reference conductors of a potentiostat EG &G PAR 273. The flow cell was connected to a syringe pump Sage with interchangeable syringes to use different solutions . The initial background measurements were made in 0.5 M K2SO4 by examining the cyclic amperometric response of the gold mesh to both a static and flow state at 0.6 milliliter per minute. The solution was changed to one containing 2.5 mM of potassium ferricyanide, 2.5 mM of potassium ferrocyanide, 10 mM of KCl and 0.5 M of K2SO4 in water and the cyclic voltiamperigrams were recorded under static and flow conditions of 0.4 milliliter per minute . There was a difference of 0.225 mA between peak anodic and peak cathodic currents at an exploration rate of 10 mv per second under static non-flow conditions. These control experiments determined that the reference electrode was stable under flow conditions and established the background current levels due to the support of the gold mesh. The 13-millimeter carbon nanotube mat disk was placed on top of the gold mesh, followed by the gasket supplied with the filter holder and upper section of the filter holder. The cell was washed with a solution containing 2.5 mM of potassium ferricyanide, 2.5 mM of potassium ferrocyanide, 10 mM of KCL and 0.5 M of K2SO4 in water. The cyclic voltiamperigrams for ferri / ferrocyanide reduction and oxidation recorded under static conditions exhibited ridge currents almost 50 times higher than those observed for the gold mesh alone. There was a 12 A difference between anodic peak and cathodic peak currents at an exploration rate of 510 mv / second under static non-flow conditions. further, the shape of the cyclic voltiamperigrams recorded at scanning regimes of 10, 20 and 40 mv / second was compatible with the oxidation and reduction of ferri / ferrocyanide entrapped within the pore structure of the carbon nanotube mat electrode. Similar cyclic voltiperimetric forms were recorded under flow conditions with a pumping rate of 0.4 milliliter per minute. The results are shown in Figure 8 which is a graphical representation of the current / voltage ratio for the materials manufactured according to Example 8 where the vertical axis represents the current and the horizontal axis represents the applied potential at various power systems. exploration of potential. The terms and expressions that have been used are used as terms of description and not as limitations and there is no intention in the use of these terms or expressions to exclude any of the equivalents of the particularities shown and described as portions thereof, being recognized that various modifications are possible within the scope of the invention.

Claims (32)

R E I V I N D I C A C I O N E S:

1. A composition of matter comprising a porous packed bed having a plurality of nanofibers and a number of scaffold particulate materials, the packed bed having a fluid flow rate characteristic for water greater than 0.5 milliliter per minute per square centimeter with a pressure differential through the packed bed of approximately 1 atmosphere when the packed bed has a thickness of 25.40 micrometers.

2. The composition according to claim 1, wherein the packed bed has a surface area greater than about 10 meters per gram.

The composition according to claim 1, wherein the nanofibers have an average diameter of less than 0.1 micron and the scaffold particles have a first dimension greater than about 1 micron and a second dimension greater than about 0.5 micron.

The composition according to claim 1, wherein the packed bed has at least one fluid flow characteristic that is at least twice as large as a packed bed of nanofibers without the scaffolding particulate materials.

5. The composition according to claim 1, wherein the packed bed comprises 1 weight percent to 99 weight percent nanofibers and 99 weight percent to 1 weight percent of scaffold particulate materials.

The composition according to claim 1, wherein the packed bed comprises 5 weight percent to 50 weight percent nanofibers and 90 weight percent to 60 weight percent scaffold material.

The composition according to claim 1, wherein the packed bed comprises a voidless solid volume having a volume percent to 99 volume percent nanofibers and 99 volume percent to 1 volume percent scaffolding particles materials.

The composition according to claim 1, wherein the packed bed comprises a voidless solid volume having from 5 volume percent to 50 volume percent nanofibers and from 90 volume percent to 60 percent in volume. volume of materials in scaffolding particles.

The composition according to claim 1, wherein the nanofibers have a diameter less than about 0.5 micron and a length-to-diameter ratio greater than about 5.

The composition according to claim 1, wherein the nanofibers They are carbon fibrils that are essentially cylindrical with an essentially constant diameter of less than 0.5 micron, having graffitic layers concentric with the axis of the fibril and being essentially free of pyrolytically deposited carbon.

The composition according to claim 1, wherein the scaffold particulate materials are of an appropriate configuration and size to provide a scaffolding effect within the packed bed.

The composition according to claim 1, wherein the scaffold particulate materials have a particulate configuration that is selected from a fiber, an irregular solid, a sphere, a platelet, a disk, a pyramid or a cube.

13. The composition of matter according to claim 1, wherein the scaffold particulate materials are fibers having an average diameter at least 10 times greater than the average diameter of the nanofiber.

14. The composition according to claim 1, wherein the nanofibers and the scaffold particulate materials comprise carbon.

15. The composition according to claim 1, wherein the nanofibers are carbon nanofibers and the scaffolding materials are carbon fibers.

The composition according to claim 1, wherein the packed bed has essentially isotropic physical properties in at least two dimensions.

17. The composition according to claim 1, which also comprises additives in dispersed particles within the packed bed.

The composition according to claim 15, wherein the particulate additives are present in an amount ranging from 0.01 percent to 25 percent.

A method for preparing a porous packed bed having a plurality of nanofibers and a number of scaffold particulate materials comprising the steps of: (a) dispersing the nanofibers and the scaffold particles in a medium to form a suspension; and (b) separating the medium from the suspension so as to form the packed bed.

The method according to claim 19, wherein the medium is selected from the group consisting of water and organic solvents.

21. The method according to claim 19, wherein the step of separating comprises filtering the suspension.

22. The method according to claim 19, wherein the step of separating comprises evaporating the medium from the suspension.

23. The method according to claim 19, wherein the suspension is a gel or paste comprising the nanofibers and the scaffold particles in a fluid and the separation comprises the steps of: (a) heating the gel or paste in a pressure vessel up to a temperature above the critical temperature of the fluid; (b) removing the supercritical fluid from the pressure vessel; and (c) removing the packed porous composite bed from the pressure vessel.

24. A porous through-flow electrode comprising a porous packed bed having a plurality of nanofibers and a number of scaffold particulate materials, the packed bed has a porosity greater than 50 percent and a fluid flow rate characteristic for water greater than a thickness of 0.5 millimeter per minute per square centimeter per micrometer at a pressure through the packed bed of approximately 1 atmosphere when the packed bed has a thickness of 25.40 micrometers.

25. The porous through-flow electrode according to claim 24, further comprising means for electrically connecting the electrode.

26. The porous through-flow electrode according to claim 25, wherein the means for electrically connecting is a conductive wire or a conductive flat surface in conductive contact with the electrode.

27. The porous through-flow electrode according to claim 24, wherein the packed bed is held in a conductive mesh support.

28. The porous through-flow electrode according to claim 25, wherein the means for electrically connecting is a current collector that provides a support for the packed bed.

29. A method for preparing a porous through-flow electrode comprising a porous packed bed having a plurality of nanofibers and a number of scaffold particulate materials, comprising the steps of: (c) dispersing the nanofibers and the materials in Scaffold particles in a medium to form a suspension; and (d) separating the medium from the suspension to form the packed bed, wherein the step of separating comprises filtering the medium through a support consisting of a conductive mesh to result in the porous electrode remaining in conductive contact with the conductive mesh

30. A filter medium comprising the composition according to claim 1.

31. An adsorbent medium comprising the composition according to claim 1.

32. A solid phase for chromatographic separation comprising the composition according to the claim 1.