CN111424337B

CN111424337B - Method for preparing chiral reversal graphene liquid crystal through nano fluid rectification

Info

Publication number: CN111424337B
Application number: CN202010264288.9A
Authority: CN
Inventors: 武培怡; 刘艳军
Original assignee: Donghua University
Current assignee: Donghua University
Priority date: 2020-04-07
Filing date: 2020-04-07
Publication date: 2021-06-11
Anticipated expiration: 2040-04-07
Also published as: CN111424337A

Abstract

The invention relates to a method for preparing chiral reversal graphene liquid crystal through nano-fluid rectification, wherein the material is obtained by using components including sodium alginate, glucose and graphene oxide GO, guiding the sodium alginate to migrate outwards through calcium ions to form polymer nano-fluid and driving GO to reverse. The method is simple to operate and easy for large-scale production, and the prepared liquid crystal microfiber has a long-range ordered structure, a stable topological configuration and a controllable optical appearance, and has wide application prospects in basic soft substance research and specific optical sensing and identification.

Description

Method for preparing chiral reversal graphene liquid crystal through nano fluid rectification

Technical Field

The invention belongs to the field of graphene liquid crystal materials, and particularly relates to a method for preparing chiral reversal graphene liquid crystal through nanofluid rectification.

Background

The colloidal liquid crystal formed by the nano-particles has special structure and topology, which attracts the extensive attention of researchers. (y.li, et al, nat. commun.2016,7,12520). This unique structure and topology can be used for the study of basic soft materials or as a template for the production of new materials for other complex structures (k.e. shopsowitz, et al, Nature 2010,468, 422-.

Graphene Oxide (GO) is a graphene derivative containing oxygen atoms that spontaneously assembles into a liquid crystal solution at a critical concentration (y.h.shim, et al, mater.horiz.2017,4, 1157-. GO liquid crystal is a new type of two-dimensional colloid, attracting high attention of researchers due to its special electrical, optical and nanocomposite properties (y.h.shim, et al, mater.horiz.2017,4, 115-. However, in many practical applications it is required that GO liquid crystals have a long range order structure and a stable topological configuration. For GO liquid crystal colloids with liquid flow properties, it is very difficult to obtain long range order structures and stable topological configurations.

Researchers have obtained long-range order structure and topological configuration stability of GO liquid crystal by means of external stimuli such as electric field, magnetic field, mechanical shear and chemical interface stability (t.z.shen, et al, nat. mater.2014,13, 394-399; j.e.kim, t.h.han, et al, angelw.chem., int.ed.2011,50, 3043-3047; y.jiang, et al, nat. Commun.2019,10,4111; y.xia, et al, Nature 2018,557, 409-412). However, these manufacturing strategies generally require expensive equipment and complex manufacturing techniques. So far, there is no simplicity. An effective and feasible method is used for directly preparing a large-scale GO liquid crystal material with a multi-level ordered structure and a stable external appearance. High-grade (c.gao, et al., j.energy.chem.2019, 34, 104-. Studies have shown that surface wrinkles and a large number of defects in the interior have a dramatic effect on the electrical and mechanical properties of the fibers (m.k.shin, et al., nat. commun.2012,3, 650.).

On the basis of single axial shear force of wet spinning injection flow, horizontal shear force is introduced to provide radial shear force to polymer flow, and internal GO lamella is guided to be reversely assembled to form the chiral reversed liquid crystal fiber. During the preparation process, reverse assembly of the internal GO and formation of the hydrogel skin with outer layer protection are performed simultaneously. The method is simple to operate and easy for large-scale production, and the prepared liquid crystal microfiber has a long-range ordered structure, a stable topological configuration and a controllable optical appearance, and has wide application prospects in basic soft substance research and specific optical sensing and identification. In addition, the chiral reversed GO liquid crystal fibers keep the stability of the internal structure in the drying process, finally the GO fibers with high mechanical strength and flexibility are obtained, and the GO liquid crystal fibers have wide application prospects in the fields of electrochemistry, sensing and the like.

CN 110607569A discloses a method for preparing nano-cellulose liquid crystal microfibril by two-dimensional domain-limited self-assembly, wherein the nano-cellulose is in a nano-scale short rod shape, and the shear force horizontally provided to polymer flow can only promote the assembly of the nano-cellulose and can not realize the chiral inversion of a liquid crystal array. In addition, compared with the liquid crystal microfiber prepared from the short rod-shaped nano cellulose, the liquid crystal microfiber has a single application scene in the field of responsivity chiral optics; based on the conductivity of graphene and the rapid ion migration channel between sheets, the liquid crystal fiber prepared from the sheet graphene also has great application prospects in the fields of electrochemistry, energy storage and the like.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a method for preparing a chiral reversal graphene liquid crystal through nanofluid rectification, and the method overcomes the defect that a large-scale long-term stable liquid crystal sheet layer alignment structure cannot be constructed under the condition without external force action (such as an electric field, a magnetic field, mechanical shearing, chemical riveting and the like) in the prior art.

The invention provides a chiral reversal graphene liquid crystal material which is obtained by guiding sodium alginate to migrate outwards through calcium ions to form polymer nanofluid and driving GO to reverse by using components comprising sodium alginate, glucose and graphene oxide GO; wherein the mass percent concentration of the sodium alginate in the components is 0.2-1.5wt%, the mass percent concentration of the glucose is 1-10wt%, and the mass percent concentration of the GO is 0.05-0.3 wt%.

Preferably, the mass percent concentration of the sodium alginate in the component is 0.5-1wt%, the mass percent concentration of the glucose is 3-8wt%, and the mass percent concentration of the GO is 0.1-0.25 wt%.

Further, preferably, the mass percentage concentration of sodium alginate in the component is 0.5wt%, the mass percentage concentration of glucose is 5wt%, and the mass percentage concentration of GO is 0.2 wt%.

The size of the graphene oxide GO is 500 μm.

The liquid crystal material has a radial topology and an axial wheatear topology inside.

The invention relates to a preparation method of a chiral reversal graphene liquid crystal material, which comprises the following steps:

(1) polymer incorporation to provide radial shear: adding sodium alginate and glucose into the graphene oxide GO solution, and stirring to obtain an injection; wherein the mass percent concentration of the sodium alginate in the injection is 0.2-1.5wt%, the mass percent concentration of the glucose is 1-10wt%, and the mass percent concentration of the GO is 0.05-0.3 wt%;

salt solution preparation to drive polymer outward migration: preparing a calcium chloride coagulating bath, which specifically comprises the following steps: adding calcium chloride into deionized water, and performing ultrasonic dispersion to obtain a coagulating bath containing a large amount of calcium ions;

(2) injecting the injection into a calcium chloride coagulation bath through an injector, guiding sodium alginate to migrate outwards by calcium ions to form polymer nanofluid, driving GO to invert to obtain chirally inverted GO liquid crystal microfibers, and obtaining the chirally inverted graphene liquid crystal material.

The preferred mode of the above preparation method is as follows:

the molar concentration of calcium chloride in the coagulation bath in the step (1) is 10-100 mM.

Further, the molar concentration of calcium chloride in the coagulation bath is 50-80 mM.

Further, the molarity of the coagulation bath calcium chloride was 50 mM.

The injection speed in the step (2) is 0.5-4 mL/min; the injection speed was controlled by a peristaltic pump.

Preferably, the injection rate is 1-2 mL/min.

Further, it is preferable that the injection rate is 1.5 mL/min.

The GO liquid crystal microfibers in the step (2) are provided with a cholesteric liquid crystal array with chiral inversion.

The invention provides a chiral reversal graphene liquid crystal material prepared by the method.

The invention provides an application of the chiral reversal graphene liquid crystal material.

At present, colloidal liquid crystals formed by nanoparticles with special structures and topologies attract the attention of researchers. The nano-particle colloidal liquid crystal with a long-range ordered structure and a stable topological configuration is constructed, and the nano-particle colloidal liquid crystal has wide application prospects in the aspects of soft substance foundation research, optics, electrochemistry, energy storage and the like. In addition, the long-range ordered multi-level structure can be used as a template to construct other novel functional materials by introducing optical, electrical, magnetic and other functional materials.

According to the invention, the chiral reversal graphene liquid crystal is prepared through nanofluid rectification, and on the basis of single axial shear force of a wet spinning injection flow, a horizontal direction is introduced to provide radial shear force for a polymer flow, and the graphene oxide sheet layers inside are guided to be reversely assembled to form the chiral reversal liquid crystal fiber. The method is simple to operate and easy for large-scale production, and the prepared liquid crystal microfiber has a long-range ordered structure, a stable topological configuration and a controllable optical appearance, and has wide application prospects in basic soft substance research and specific optical sensing and identification.

In the preparation process, sodium alginate in the injection migrates outwards at the GO liquid crystal fiber interface and is rapidly crosslinked with calcium ions in a coagulating bath to form a smooth and stable hydrogel skin which is used as a protective layer to maintain the stability of the topological configuration of the liquid crystal fiber.

In the invention, the sodium alginate is in AR grade, the purity is 90%, the mass percent concentration of the sodium alginate is 0.2-1.5wt%, and when the concentration of the sodium alginate is too low, the liquid crystal microfiber is not easy to form a stable and smooth hydrogel skin; sodium alginate concentration is too high, and viscosity is too high, so that quick arrangement and assembly of GO sheets are not facilitated.

According to the invention, the molar concentration of calcium chloride in the coagulation bath is 10-100mM, and when the concentration of calcium chloride is too low, the polymer sodium alginate in the coagulation bath lacks sufficient traction force, so that a stable and smooth hydrogel skin is difficult to form at the interface; the concentration of calcium chloride is too high, and the excessive calcium ions are crosslinked with sodium alginate, so that the liquid crystal fiber is not easy to take out from the receiving liquid.

According to the invention, the liquid crystal microfiber shows uniform interference color under polarized light by the aid of the chiral reversed GO liquid crystal array.

Advantageous effects

(1) The invention has simple assembly equipment and simple assembly strategy, is efficient, can be produced in large scale and is beneficial to industrialized popularization and use.

(2) According to the invention, by introducing the polymer shear flow in the horizontal direction, the rapid assembly of GO lamella is promoted, and the chiral inversion of GO liquid crystal is realized.

(3) The invention can maintain the stability of the internal liquid crystal configuration by means of the quickly formed hydrogel skin, and in addition, a closed curved surface is provided as a riveting interface for GO self-assembly, so that the GO cholesteric array presents radial arrangement in the radial direction, and the construction of a specific functional structure is realized.

(4) The invention drives the internal liquid crystal configuration to present the wheat ear-shaped arrangement in the axial direction by means of the combined action of the horizontal polymer shear flow and the axial vertical injection flow.

(5) By introducing glucose, the invention can maintain the stability of the internal structure on the basis of not influencing the internal liquid crystal configuration, so that the dried fiber still has an ordered internal structure. The mechanical strength, elongation and modulus were increased by about 4 times, 2 times and 4 times, respectively, relative to the liquid crystal fiber without glucose.

(6) The GO liquid crystal fiber obtained by the invention shows uniform interference color under polarized light, and the color is regularly switched along with the change of axial stress, and the color of the liquid crystal fiber is gradually switched from red to blue when the stress is increased.

(7) The invention realizes the chiral inversion of GO liquid crystal, and the synchronously formed hydrogel skin is used as a protective cover to maintain the stability of the internal liquid crystal configuration. In addition, the glucose balancing interfacial energy and elastic energy within the GO liquid crystal fibers enable the fibers to maintain a stable and smooth surface of the internal structure during drying. As can be clearly seen from fig. 8(a), the surface of the GO liquid crystal fiber without glucose generates a lot of ravines, and the distortion of the surface finally results in the destruction of the internal ordered structure; in contrast, after addition of glucose, the GO liquid crystal fibers shrink uniformly and the internal ordered structure can be retained.

Drawings

FIG. 1 is a schematic diagram of the preparation process of the chiral reversed GO liquid crystal microfiber, a schematic diagram of the synergy of horizontal polymer shear flow and vertical injection flow, and a schematic diagram of the mechanism of the formation of the outer layer protective hydrogel skin.

FIG. 2 is an optical microscope photograph of the core-sheath structure formed by the liquid crystal fiber of the present invention and traces of internal horizontal shear flow and vertical injection flow.

FIG. 3 is a radial cut view of dried GO fibers of the present invention.

Fig. 4 is a schematic representation (a) of a cholesteric array of GO with chiral inversion in the present invention, and a chiral contrast (B) of GO solution and GO liquid crystal fibers in example 1.

Fig. 5 is a graph of (a) radial and (B) axial polarization of chiral reversed GO liquid crystal fibers prepared in example 1.

FIG. 6 is a radial polarization diagram and internal configuration schematic of liquid crystal fibers of different GO concentrations (a), (b), and (c) prepared in example 2.

Fig. 7 is a graph (a) of the uniform change in color during stretching of the chiral reversed GO liquid crystal fiber prepared in example 1, and a corresponding CD graph (B) of the change in pitch of the cholesteric array.

Fig. 8 is a scanning electron microscope image (a) and a tensile stress-strain image (B) of the chiral reversed GO liquid crystal fiber prepared in example 1 after drying.

Fig. 9 is a plot of the polarized light of the rough surface GO liquid crystal fiber prepared in comparative example 2.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.

Example 1

1) Polymer incorporation to provide radial shear: adding 0.05g of sodium alginate powder (AR grade, purity of 90 percent, Shanghai Aladdin Biotechnology Co., Ltd.) and 0.5g of glucose powder (AR grade, Shanghai Aladdin Biotechnology Co., Ltd.) into 10mL of GO (particle size of 50 mu m) solution, and magnetically stirring for 10min to prepare a uniform injection, wherein the mass fraction of GO in the GO solution is 0.2 wt%;

2) salt solution preparation to drive polymer outward migration: 2.775g of anhydrous calcium chloride (Shanghai Aladdin Biotechnology Co., Ltd.) is added into 500mL of deionized water, and ultrasonic treatment is carried out for 5min under the condition of 100W ultrasonic wave to prepare 50mM calcium chloride coagulation bath;

3) preparation of chirally inverted GO liquid crystal fibers

Injecting the receiving liquid obtained in the step 1) into the calcium chloride coagulating bath obtained in the step 2) through an injector, wherein the injection speed of the injector is controlled to be 1.5mL/min through a peristaltic pump, and then the GO liquid crystal fiber with chiral reversal of GO cholesteric array, long-range order of internal structure, stable liquid crystal configuration and controllable optical appearance can be obtained.

As shown in fig. 2, it is shown that: rapid reverse assembly of the inner GO sheets and rapid formation of the outer protective layer hydrogel skin can be achieved simultaneously by simple nanofluid rectification techniques.

As shown in fig. 4, it is shown that: compared with the alignment of the clockwise helices of the GO cholesteric array in the liquid crystal solution, the alignment of the counterclockwise helices of the GO cholesteric array in the dynamic cylindrical geometry forms a chiral inverted liquid crystal configuration.

As shown in fig. 5, it is shown that: the radial cross pattern and axial red-blue bands of the GO liquid crystal fibers confirm the ordered multilayer structure inside the GO liquid crystal fibers, i.e., the radial topology and the axial wheatear topology.

As shown in fig. 6, it is shown that: with the increase of GO concentration, the GO cholesteric liquid crystal array continuously grows from outside to inside.

As shown in fig. 7, it is shown that: the GO liquid crystal fibers show uniform interference color under polarized light, and the color is switched from blue to red along with the increase of axial stress because the pitch of the cholesteric array is continuously reduced in the stretching process.

As shown in fig. 8, it is shown that: after the glucose is added, the GO liquid crystal fibers uniformly shrink in the drying process, maintaining the stable and smooth surface of the internal ordered structure, thereby obtaining high mechanical strength and flexibility. When no glucose is added, the elongation of the GO liquid crystal fiber is 3.8%, the tensile stress is 15MPa, and the Young modulus is 0.8 GPa; after addition of glucose, the GO liquid crystal fiber elongation increased to 10.5%, the tensile stress increased to 55MPa, and the young's modulus increased to 4.2 GPa.

And testing the tensile property of the dried GO liquid crystal fiber by adopting a GB-T1040.5-2008 mechanical property test standard. The test uses 80 μm dry GO liquid crystal fibers with a draw rate of 5mm/min, a universal mechanical tester (model: Instron 5966, from Instron) and a mechanical sensor of 1N.

Example 2

The same preparation procedure as in example 1 was followed except that the mass fraction of GO in the GO solution in step 1) was changed to 0.08 wt% at a low concentration and 0.15 wt% at a high concentration to prepare GO liquid crystal microfibers.

The GO liquid crystal fibers obtained in comparative example 1 were radially in a solid cross pattern, and with the decrease in GO concentration, the cross pattern became a hollow cross pattern and a skin-like cross pattern, since the polymer flow driven GO sheets to migrate outwards, the assembly of GO proceeded from outside to inside.

Comparative example 1

1) Adding 0.055g of anhydrous calcium chloride powder (AR grade, purity 90%, Shanghai Aladdin Biotechnology Co., Ltd.) into 10mL of GO (particle size-50 μm) solution, magnetically stirring for 10min, and preparing into uniform injection, wherein the mass fraction of GO in the GO solution is 0.2 wt%;

2) adding 2.5g sodium alginate (Shanghai Aladdin Biotechnology Co., Ltd.) into 500mL deionized water, and performing ultrasonic treatment under 100W ultrasonic wave for 10min to obtain 0.5wt% sodium alginate coagulation bath;

3) preparation of chirally inverted GO liquid crystal fibers

Injecting the injection obtained in the step 1) into the sodium alginate coagulation bath obtained in the step 2) through an injector, wherein the injection speed of the injector is controlled to be 1.5mL/min through a peristaltic pump, and then obtaining the GO liquid crystal fiber.

The GO liquid crystal fiber obtained in the comparative example 1 has high mechanical strength, excellent ductility and uniform color development, the mechanical strength of the GO liquid crystal fiber obtained in the comparative example is low, the elongation of the GO liquid crystal fiber is 1.5%, and the tensile stress is 4MPa, which is far lower than the mechanical property of the GO liquid crystal fiber obtained in the comparative example 1; furthermore, calcium ions in the injection solution continuously migrate into the receiving solution, and finally the receiving solution is also crosslinked, so that the liquid crystal fibers cannot be taken out of the receiving solution.

Comparative example 2

GO liquid crystal fibers were prepared according to the same preparation procedure as in example 1, except that the calcium chloride receiving solution in step 2) was replaced with absolute ethanol (95%) as the receiving solution.

The GO liquid crystal fibers obtained in comparative example 1 and having high mechanical strength, excellent ductility and uniform color development are low in mechanical strength and unsmooth in surface, so that liquid crystal color development is nonuniform. In the absolute ethyl alcohol coagulating bath, the sodium alginate in the injection is precipitated and hardened, and the water in the liquid crystal fiber migrates to the absolute ethyl alcohol, so that the surface of the liquid crystal fiber is stressed unevenly, and a rough surface is formed. As shown in fig. 9, it is shown that: the GO liquid crystal fiber prepared by taking absolute ethyl alcohol (95%) as receiving liquid has a rough surface and a large number of defects inside.

Comparative example 3

1) A0.38 wt% GO solution was loaded into a glass syringe and injected into a NaOH/methanol coagulation bath under nitrogen at a constant pressure of 1.5 MPa.

2) The GO liquid crystal fibers were then received with a drum, followed by washing with methanol to remove the salt and finally dried at room temperature for 24 hours to form GO fibers (z.xu, c.gao, nat. commun.2011,2,571).

In terms of the preparation method, the GO liquid crystal fiber prepared in the comparative example 3 has no reverse chirality, and a large number of folds are generated on the surface after drying. The method is simple to operate and easy for large-scale production, and the prepared liquid crystal microfiber has a long-range ordered structure, a stable topological configuration and a controllable optical appearance, and also provides a new platform for the research of other novel materials with complex structures.

Claims

1. The chiral reversal graphene oxide liquid crystal material is characterized in that the material is obtained by guiding sodium alginate to migrate outwards through calcium ions to form polymer nanofluid and driving graphene oxide GO to reverse by using components including sodium alginate, glucose and graphene oxide GO;

the chiral reversal graphene oxide liquid crystal material is prepared by the following method:

(1) adding sodium alginate and glucose into the graphene oxide GO solution, and stirring to obtain an injection; wherein the mass percent concentration of sodium alginate in the injection is 0.2-1.5wt%, the mass percent concentration of glucose is 1-10wt%, and the mass percent concentration of graphene oxide GO is 0.05-0.3 wt%;

preparing a calcium chloride coagulating bath;

(2) injecting the injection into a calcium chloride coagulating bath through an injector to obtain a chiral reversal graphene oxide liquid crystal material; wherein the molar concentration of calcium chloride in the coagulation bath is 10-100 mM.

2. The liquid crystal material of claim 1, wherein the composition comprises 0.5-1wt% of sodium alginate, 3-8wt% of glucose, and 0.1-0.25wt% of Graphene Oxide (GO).

3. The liquid crystal material of claim 2, wherein the composition comprises 0.5wt% of sodium alginate, 5wt% of glucose, and 0.2wt% of Graphene Oxide (GO).

4. The liquid crystal material of claim 1, wherein the graphene oxide GO has a size of 500 μm.

5. The liquid crystal material of claim 1, wherein the liquid crystal material has an inner portion with a radial topology and an axial wheatear topology.

6. A preparation method of a chiral reversal graphene oxide liquid crystal material comprises the following steps:

preparing a calcium chloride coagulating bath;

7. The method according to claim 6, wherein the injection rate in the step (2) is 0.5-4 mL/min; the injection speed was controlled by a peristaltic pump.

8. A chiral reversed graphene oxide liquid crystal material prepared by the method of claim 6.

9. Use of the chiral reversed graphene oxide liquid crystal material of claim 1.