WO2024123211A1 - Porous material producing method,contact lens containing said material, and porous material with gradient refractive index - Google Patents

Porous material producing method,contact lens containing said material, and porous material with gradient refractive index Download PDF

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Publication number
WO2024123211A1
WO2024123211A1 PCT/RU2023/050222 RU2023050222W WO2024123211A1 WO 2024123211 A1 WO2024123211 A1 WO 2024123211A1 RU 2023050222 W RU2023050222 W RU 2023050222W WO 2024123211 A1 WO2024123211 A1 WO 2024123211A1
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Prior art keywords
particles
layers
porous material
refractive index
base material
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PCT/RU2023/050222
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French (fr)
Inventor
Aleksey Vladimirovich ARSENIN
Valentin Sergeevich VOLKOV
Georgii Alekseevich ERMOLAEV
Alexander Vyacheslavovich SYUY
Gleb Igorevich TSELIKOV
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Xpanceo Research On Natural Science L.L.C.
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Priority claimed from RU2022132007A external-priority patent/RU2802952C1/en
Application filed by Xpanceo Research On Natural Science L.L.C. filed Critical Xpanceo Research On Natural Science L.L.C.
Publication of WO2024123211A1 publication Critical patent/WO2024123211A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D11/00—Producing optical elements, e.g. lenses or prisms
    • B29D11/00009—Production of simple or compound lenses
    • B29D11/00355—Production of simple or compound lenses with a refractive index gradient
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/58—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising fillers only, e.g. particles, powder, beads, flakes, spheres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D11/00—Producing optical elements, e.g. lenses or prisms
    • B29D11/00009—Production of simple or compound lenses
    • B29D11/00038—Production of contact lenses
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29D—PRODUCING PARTICULAR ARTICLES FROM PLASTICS OR FROM SUBSTANCES IN A PLASTIC STATE
    • B29D11/00—Producing optical elements, e.g. lenses or prisms
    • B29D11/0073—Optical laminates
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/26—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a solid phase from a macromolecular composition or article, e.g. leaching out
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
    • G02B1/041—Lenses
    • G02B1/043—Contact lenses
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2201/00—Foams characterised by the foaming process
    • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
    • C08J2201/044—Elimination of an inorganic solid phase
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2333/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers
    • C08J2333/04—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters
    • C08J2333/06—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Derivatives of such polymers esters of esters containing only carbon, hydrogen, and oxygen, the oxygen atom being present only as part of the carboxyl radical
    • C08J2333/10—Homopolymers or copolymers of methacrylic acid esters
    • C08J2333/12—Homopolymers or copolymers of methyl methacrylate
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/0066—Use of inorganic compounding ingredients
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
    • C08J9/36—After-treatment
    • C08J9/40—Impregnation

Definitions

  • the group of inventions relates to the field of optics and specifically to the method of producing porous materials for optical elements and to the porous materials with gradient refractive index, wherein said materials can be produced using said method and utilized in fiber optics, optical instrument engineering, ophthalmology to create object lenses, condenser lenses, endoscopes, interface devices between fiber optic communication lines and emission sources or optical detectors, spherical lenses, including contact lenses, with refractive index gradient, etc.
  • Various prior art methods are known that are used to produce optical materials with gradient refractive index, for example, the sol-gel method (see patent US8763430B2, cl. C03B19/12, published 01.07.2014).
  • a glass with refractive index gradient can be produced using neutron irradiation, chemical vapor deposition, ion exchange, ion implantation, crystal growing, glass layering, etc.
  • the main problem of producing the optical materials with refractive index gradient consists in technological complexity of the process and in the gradient range being limited by potential refractive indices of the used material.
  • the prior art discloses a method of producing a material with a refractive index gradient, in particular, in the form of large sheets, wherein said method consists in producing a hierarchically multilayered polymer composite from an ordered set of polymer films (of immiscible, miscible or partly miscible polymers), each having its own refractive index, after which the multilayer polymer composite sheet is formed up (see patent US7002754B2, cl. G02B3/00, published 21.02.2006).
  • the prior art method makes it possible to produce a continuous, discrete or stepwise refractive index gradient ranging from 0.01 to 1.0 in any axial, radial or spherical direction.
  • One of the options to controllably vary the properties of a material is to form voids or pores inside the material thereby varying its specific volumetric characteristics. Such method can be as well applied to vary the refractive index.
  • the prior art discloses a porous material producing method comprising the following steps: producing the particles, distributing the particles within the mass of the base material, forming a layer of the base material with the particles, exposing said layers to emission and removing the particles from the layers to form pores (see application WO2004053205A2, cl. C30B 25/10, published 24.06.2004).
  • Said method uses the particles in the form of polymer balls that are distributed within the mass of silicon by depositing the latter, using the vapor-phase deposition process, within the space between the balls that are subsequently removed by means of pyrolysis.
  • the pores are voids formed after removing a solvent from a selectively polymerized binding substance. Disadvantage of the prior art material consists in relatively low predictability and precision of the obtained optical properties.
  • the technical problem is to eliminate said disadvantage and to obtain a wide range of high-quality optical materials having high transmittance within the visible spectral range and close IR range, as well as low material dispersion, in particular, to produce multilayer contact lenses having an increased refractive index gradient.
  • the technical effect consists in simplification of the process of producing a porous material with predetermined optical properties.
  • the set problem has been solved and the technical effect has been achieved by that according to the porous material producing method, comprising the following steps: (i) producing the particles, (ii) distributing the particles within the mass of the base material, (iii) forming the layers of the base material with the particles, (iv) exposing said layers to emission, (v) removing the particles from the layers to form the pores, and (vi) producing the porous material from the layers obtained in step (v), said mass of the base material in step (ii) is represented by an optically transparent polymer, and the particles in step (i) are produced from a material having the coefficient of absorption of the emission used in step (iv) higher than that of said base material, wherein in step (iv) said emission is used to heat up the particles and partly evaporate the base material around them so that to make it possible to remove these particles in step (v), and the pores formed after removing the particles are
  • Step (i) involves producing the particles having the diameter d , and in step (iii) the layers of the base material with the particles are preferably formed on substrates by using the centrifugation process and are polymerized, wherein the layer of the base material is formed with the thickness from 0.2 d to 1.2 d .
  • said porous material is preferably formed by superimposing the layers produced in step (v), using the liquid transfer method.
  • the porous material can be formed in a fixture with spherical inner surface.
  • the porous material can be formed of at least two layers with different concentration of pores, wherein for said layers in step (ii) the particles within the mass of the base material are distributed in different concentrations.
  • said layers are preferably stacked in such a way that the pore concentration therein increases from one side of the porous material towards the other.
  • the particles are preferably produced from a source crystal using the method of femtosecond laser fragmentation or ablation in liquid with the absorption cross-section area S being such that S ⁇ I > 10 -7 W , where I is the power density of the emission used in step (iv).
  • the produced porous material is preferably provided with an impermeable outer coating. The produced porous material can be used in contact lens production.
  • the technical effect as related to the device, consists in expanding functionality of the porous material by providing increased variability of its optical properties.
  • the set problem has been solved and the technical effect has been achieved by that the porous material having a gradient refractive index, which is implemented as a mass of the base material of optically transparent polymer with the pores distributed therein, is formed by at least two layers with different refractive indices, said layers having pores distributed therein in different concentrations and filled with a substance having a refractive index different from the refractive index of the base material.
  • step (v) represents the general view of layer 2 with pores 1 formed after removing particles 3 in step (v);
  • the subject matter of the suggested invention consists in producing an optical material having predetermined properties by means of forming pores 1 within mass 2 of an optically transparent polymer. Said pores can be formed in various concentrations and filled with air or another substance.
  • porous material producing method consisting in using high-absorptive particles 3 and implementing the following main steps.
  • particles 3 having the diameter d (maximum linear dimension) ranging from 10 to 10000 nm are produced from a high-absorptive material by using the method of femtosecond laser fragmentation [Besner, S., Kabashin, A.V., Meunier, Y. «Fragmentation of colloidal nanoparticles by femtosecond laser-induced supercontinuum generation» Appl. Phys. Let.
  • high-absorptive material should be understood as a material whose coefficient of absorption of the emission used in step (iv) is higher than that of said base material 2 (polymer) used in step (ii).
  • the target dimension (diameter) of the produced particles 3 is chosen so that the area of the absorption cross-section S meets the condition:
  • I is the power density of the emission used in step (iv).
  • the most preferable alternatives of said high-absorptive material are nanoclusters of the noble metals such as gold or silver, as well as two-dimensional materials such as molybdenum disulfide, tungsten disulfide, tungsten diselenide, and others.
  • Laser fragmentation or ablation are carried out using a femtosecond pulse laser.
  • the particles are obtained directly from the crystal surface, while in the process of fragmentation – from a mixture of crystalline powder with relatively large crystals and a solvent under constant stirring of the liquid until the target concentration of particles 3 is achieved in the produced solution.
  • Diameter d of particles 3 synthesized in this step may vary in the range from 10 to 10000 nm, but preferably is in the range from 1 to 250 nm.
  • the size-selective deposition of particles 3 is carried out using the centrifugation process with the rotation speed increasing from 200 to 8000 rpm, which results in forming monodispersed solutions.
  • Step (ii) of distributing the particles within the mass of the base material Step (ii) of distributing the particles within the mass of the base material.
  • the mass of the base material 2 is represented by an optically transparent polymer (vitreous, crystalline, or elastomeric).
  • the most suitable for such application are such polymers as polyvinyl alcohol (PVA, (C 2 H 4 O) n ), hydroxyethyl methacrylate, polydimethylsiloxane (PDMS, (C 2 H 6 OSi) n ), polylactide (PLA, (C 3 H 4 O 2 ) n ), polymethyl methacrylate (PMMA, (C 5 H 8 O 2 ) n ), polymethylpentene (PMP, (C 6 H 12 ) n ), polycarbonate (PC, (C 16 H 14 O 3 ) n ) or polyetherimide (PEI, (C 37 H 24 O 6 N 2 ) n ), which have the refractive index in the range from 1.3 to 1.8.
  • PVA polyvinyl alcohol
  • PDMS polydimethylsiloxane
  • PDMS polyd
  • polymers as polyethylene naphthalate and isomers thereof, such as 2,6-, 1,4-, 1,5-, 2,7- and 2,3-polyethylene naphthalate; polyalkylene terephthalates, such as polyethylene terephthalate, polybutylene terephthalate and poly- 1,4-cyclohexanedimethyleneterephthalate; polyimides, such as polyacrylimides; styrene polymers, such as atactic, isotactic and syndiotactic polystyrene, ⁇ -methylpolystyrene, para-methylpolystyrene; polycarbonates, such as bisphenol-A-polycarbonate; poly(meth)acrylates, such as poly(isobutylmethacrylate), poly(propylmethacrylate), poly(ethylmethacrylate), poly(methylmethacrylate), poly(butylacrylate) and poly(methylacrylate) (as used herein,
  • copolymers as styrene-acrylonitrile copolymer, preferably containing 10 to 50 wt%, preferably 20 to 40 wt%, of acrylonitrile, styrene and ethylene copolymer; and poly(ethylene-1, 4-cyclohexylendimethyleneterephthalate).
  • Further polymers include acrylic rubber; isoprene; isobutylene-isoprene; butadiene rubber; butadiene-styrene-vinylpyridine; butyl rubber; polyethylene; chloroprene; epichlorohydrin rubber; ethylene-propylene; ethylene-propylene-diene; nitrile-butadiene; polyisoprene; silicone rubber; styrene-butadiene.
  • bulk-polymerized or grafted copolymers are bulk-polymerized or grafted copolymers; butadiene-styrene-vinylpyridine; butyl rubber; polyethylene; chloroprene; epichlorohydrin rubber; ethylene-propylene; ethylene-propylene-diene; nitrile-butadiene; polyisoprene; silicone rubber; styrene-butadiene, and urethane rubber.
  • particles 3 are distributed within the mass of the base material 2 in various concentrations.
  • Step (iii) of forming the layers of the base material with the particles Step (iii) of forming the layers of the base material with the particles.
  • the layers of the base material 2 with particles 3 are preferably formed on substrates 4 by using the centrifugation process (spin coating) (Mouhamad Y., Mokarian-Tabari P., Clarke N., Jones R. A. L., and Geoghegan M. «Dynamics of polymer film formation during spin coating», Journal of Applied Physics 116, 123513, 2014).
  • spin coating the base material 2 in the form of liquid polymer with particles 3 having the diameter d is applied on substrate 4 that is rotating at predetermined angular speed and provides the target thickness of polymer layer 2.
  • the layer is formed with the thickness from 0.2 d to 1.2 d , i.e. not less than 2 nm, but not more than 12000 nm.
  • layer 2 is polymerized using ultraviolet (UV) irradiation.
  • UV ultraviolet
  • layers 2 with required thickness are formed beforehand and then used to place particles 3 therein.
  • Step (iv) of exposing the formed layers to emission is a simple process for exposing the formed layers to emission.
  • electromagnetic emission having the power density I on the order of 10 4 W/m 2 is used to heat up particles 3 and thereby to partly evaporate base material 2 around them so that to make it possible to remove these particles in the next step.
  • the diameter of the formed pores 1 will be 10–30 % more than the diameter of the used particles 3.
  • the maximum achievable size corresponds to approximately 1.3 diameters of the particles due to a rapid drop of the temperature field with the distance from particle 3.
  • the size of pores 1 can be varied as well by varying the duration of the emission. Thereby, it is possible to additionally control the effective total volume of pores 1 within the formed layer 2.
  • Step (v) of removing the particles to form the pores Step (v) of removing the particles to form the pores.
  • particles 3 are removed from the formed layers 2 by rinsing to produce, as a matter of fact, a polymer film with through holes (pores 1) of the required concentration. Hence, particles 3 can be reused in the next production cycle implementing the suggested method.
  • Pores 1 formed after removing particles 3 are filled in the current and/or the next step with a substance having the optical properties (refractive index) different from the corresponding properties of the base material 2 (refractive index 1.3–1.8).
  • a substance having the optical properties (refractive index) different from the corresponding properties of the base material 2 reffractive index 1.3–1.8.
  • the produced layers 2 in the form of a polymer film of the required porosity will have a lower effective refractive index (up to 1.2) than the base material 2 and a low dispersion value (in the range from 0.01 to 0.1 depending on pore concentration, i. e. on the total volume thereof).
  • Step (vi) of producing a porous material with predetermined optical properties Step (vi) of producing a porous material with predetermined optical properties.
  • the target porous material is produced by superimposing the layers obtained in step (v), using the liquid transfer method [R.S. Weatherup, «2D Material Membranes for Operando Atmospheric Pressure Photoelectron Spectroscopy», Topics in Catalysis 61, 2085-2102, 2018].
  • Said liquid can be water, alcohol, acetone, or a target substance with a different refractive index to fill pores 1 with. If pores 1 are to be filled with liquid, the produced porous material is provided with an impermeable outer coating (encapsulated) in submersed state. If pores 1 are to be filled with air or another gas, the produced material is retrieved and encapsulated in a suitable atmosphere. If filled with air, an impermeable outer coating is not required.
  • the produced target porous material is finally fastened together by natural bonding resulting from the affinity of polymer layers 2, or by means of final polymerization by exposing to UV emission.
  • the porous material in step (vi) can be produced from at least two layers with different concentrations of pores 1, that is with different optical properties (in particular, the refractive index).
  • said layers 2 are stacked in the thickness direction in such a way that the concentration of pores 1 therein increases from one side of the porous material towards the other .
  • the pores are filled with air, it is possible to produce a porous material in the form of an up to 100 mm thick multilayer polymer sheet having the axial refractive index gradient in the range from 0.01 to 0.6 and a low spectral dispersion value.
  • the porous material is formed in fixture 5 with spherical inner surface in an onion-like pattern
  • the polymer layers 2 with different concentrations of pores 1 varying from one side of the flat porous material towards the other are similarly laid to form a radial-spherical refractive index gradient .
  • the porous material produced using the disclosed method can be used in contact lens production to form a refractive index gradient or for other purposes.
  • An independent subject matter of the suggested invention is the porous material having a gradient refractive index, which is implemented as a mass of the base material of optically transparent polymer formed by two or more layers with different refractive indices, said layers having pores 1 distributed therein in different concentrations and filled with a substance having a refractive index different from the refractive index of the base material 2.
  • Such material can be produced using the above described method or any other method that makes it possible to produce it.
  • the common inventive conception of the group of inventions consists in modifying the optical properties of a material by forming pores 1 and filling thereof with a substance having a refractive index different from the refractive index of the base material 2.
  • the substances to fill the nanopores with can be colorants, fluorescent and magnetic substances, etc.
  • Such implementation makes it possible to significantly expand functionality of the porous material by providing increased variability of its optical properties and refractive properties (the refractive index gradient inside the multilayer material can be continuous, discrete or stepwise in any axial, radial or spherical direction, and not necessarily monotonous).
  • optical articles corresponding to the suggested group of inventions can provide good intermediate vision, possess the property of accommodation, have high transparency (transmittance up to 99% for the spectral interval in the range of 300–2000 nm), low spectral dispersion value (up to 0.01, which provides significant decrease of chromatic aberrations) and increased refractive index gradient (which, in its turn, makes it possible to expand the field of view up to 200 degrees).
  • they can provide enhanced water and air permeability, which is critical for wearable optical elements such as a contact lens.
  • such materials have relatively low cost of production and can be produced in the form of large sheets.
  • a femtosecond laser was used having the pulse length of 100 fs, pulse energy of 100 ⁇ J, wavelength of 1030 nm, and recurrence frequency of 10 kHz.
  • the source MoS 2 crystal resided in deionized water, and, using a galvo-scanner, the crystal surface was scanned by a focused laser spot at the scan speed of 1 m/s. The exposure to radiation continued until achieving the final particles concentration of 0.1 mg/ml. Then, using the centrifugation process, from the produced colloidal solution a monodispersed fraction was derived, having the average particles diameter of 100 nm and the dispersion of size distribution not more than 10 %.
  • step (ii) the particles were distributed within the base material, for which purpose the obtained solutions having the particle volume content of 0, 5, 10, 15, 20, 25, 30, and 35 % were mechanically mixed in a polymethyl methacrylate polymeric solution.
  • step (iii) the produced mixture was exposed to ultrasound and then the centrifugation process (spin coating) was used to form the 100 nm thick layers having the nanoparticle volume content of 0, 5, 10, 15, 20, 25, 30, and 35 %.
  • each of the layers was exposed to laser irradiation with the wavelength of 633 nm and intensity of 10 kW/cm 2 , which resulted in evaporation of the polymer around the nanoparticles.
  • step (v) the produced films were peeled from the substrates, thereby automatically removing the particles as they were left on the substrate. This resulted in forming the nanopores with the volume concentration of 0, 10, 20, 30, 40, 50, 60, and 70 %, and achieving the effective refractive index of 1.5, 1.45, 1.4, 1.35, 1.3, 1.25, 1.2, and 1.15.
  • step (vi) the liquid transfer method was used to transfer the layers one over another to form a multilayer porous polymer sheet.
  • the transmittance of the produced porous material with the refractive index gradient as measured at the 750 nm wavelength was 99%, while the refractive index dispersion in the range of 300–1000 nm was 0.01.
  • step (i) the high-absorptive MoS 2 particles were produced similarly to Example 1.
  • step (ii) a 100 nm thick layer of polymethyl methacrylate was coated with the MoS 2 particles by means of direct application with particle surface coating of 0, 10, 20, 30, 40, 50, 60, and 70%.
  • the transmittance of the produced porous material with the refractive index gradient as measured at the 750 nm wavelength was 99%, while the refractive index dispersion in the range of 300–1000 nm was 0.01.
  • step (vi) the bottom surface of the porous layers of polymethyl methacrylate, having the volume content of pores of 0, 10, 20, 30, 40, 50, 60, and 70%, was coated with a monolayer of graphene. Then, the pores were filled with water, and the second layer of graphene was applied to form thereby an impermeable outer coating. Thereafter, the liquid transfer method was used to transfer the layers one onto another to form a multilayer porous polymer sheet similarly to Example 1, and then onto the inner side of the contact lens.
  • the light reflection at the contact lens-to-eye border will decrease to 1 %, as the porous polymer material filled with water will have the refractive index very close to the refractive index of an eye (the difference in refractive indices is less than 0.02). In such a way, the peripheral vision aberrations can be significantly reduced.

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Abstract

A method of producing porous materials for optical elements, to the contact lenses and to the porous materials with gradient refractive index. A porous material producing method comprised of following steps: (i) producing the particles, (ii) distributing the particles within the mass of optically transparent polymer, (iii) forming the layers, (iv) exposing said layers to emission, (v) removing the particles from the layers to form the pores, and (vi) producing the porous material from these layers. In step (iv) said emission is used to heat up the particles and partly evaporate the base material around the particles so that they can be removed. In step (v) the formed pores are filled with a substance having a refractive index different from the refractive index of the base material. It simplifies the process of producing and expand functionality of a porous material with predetermined optical properties.

Description

POROUS MATERIAL PRODUCING METHOD,CONTACT LENS CONTAINING SAID MATERIAL, AND POROUS MATERIAL WITH GRADIENT REFRACTIVE INDEX
The group of inventions relates to the field of optics and specifically to the method of producing porous materials for optical elements and to the porous materials with gradient refractive index, wherein said materials can be produced using said method and utilized in fiber optics, optical instrument engineering, ophthalmology to create object lenses, condenser lenses, endoscopes, interface devices between fiber optic communication lines and emission sources or optical detectors, spherical lenses, including contact lenses, with refractive index gradient, etc.
Various prior art methods are known that are used to produce optical materials with gradient refractive index, for example, the sol-gel method (see patent US8763430B2, cl. C03B19/12, published 01.07.2014). Also, a glass with refractive index gradient can be produced using neutron irradiation, chemical vapor deposition, ion exchange, ion implantation, crystal growing, glass layering, etc. The main problem of producing the optical materials with refractive index gradient consists in technological complexity of the process and in the gradient range being limited by potential refractive indices of the used material.
The prior art discloses a method of producing a material with a refractive index gradient, in particular, in the form of large sheets, wherein said method consists in producing a hierarchically multilayered polymer composite from an ordered set of polymer films (of immiscible, miscible or partly miscible polymers), each having its own refractive index, after which the multilayer polymer composite sheet is formed up (see patent US7002754B2, cl. G02B3/00, published 21.02.2006). The prior art method makes it possible to produce a continuous, discrete or stepwise refractive index gradient ranging from 0.01 to 1.0 in any axial, radial or spherical direction. Furthermore, a dynamic reversible variation of the refractive index gradient can be achieved, which makes it possible to vary the focal distance of the lenses made from said material. Disadvantages of the prior art method are the complexity of production, including the necessity to use thermoplastic polymers, as well as impossibility to produce a material having the transmittance higher than 50% in the visible spectral range.
One of the options to controllably vary the properties of a material is to form voids or pores inside the material thereby varying its specific volumetric characteristics. Such method can be as well applied to vary the refractive index.
The prior art discloses a porous material producing method comprising the following steps: producing the particles, distributing the particles within the mass of the base material, forming a layer of the base material with the particles, exposing said layers to emission and removing the particles from the layers to form pores (see application WO2004053205A2, cl. C30B 25/10, published 24.06.2004). Said method uses the particles in the form of polymer balls that are distributed within the mass of silicon by depositing the latter, using the vapor-phase deposition process, within the space between the balls that are subsequently removed by means of pyrolysis. The main disadvantages of the prior art method are difficulty of implementation due to the necessity to use a system to chemically deposit the materials from a vapor phase, high consumption of the particles and poor controllability of the process, as well as limited functionality of the materials produced using such method (it is not evident how this method can be used to produce a material with varying optical properties).
The closest, in terms of technical substance, to the claimed invention, as related to the device, is the porous material with a gradient refractive index formed as a mass of the base material of optically transparent polymer with the pores distributed therein and filled with a substance having a refractive index different from that of the base material, to form a refractive index gradient through the thickness of the material (see application WO2011129848A1, cl. B29D 7/01, published 20.10.2011). In the prior art material, the pores are voids formed after removing a solvent from a selectively polymerized binding substance. Disadvantage of the prior art material consists in relatively low predictability and precision of the obtained optical properties.
The technical problem is to eliminate said disadvantage and to obtain a wide range of high-quality optical materials having high transmittance within the visible spectral range and close IR range, as well as low material dispersion, in particular, to produce multilayer contact lenses having an increased refractive index gradient.
The technical effect, as related to the method, consists in simplification of the process of producing a porous material with predetermined optical properties. The set problem has been solved and the technical effect has been achieved by that according to the porous material producing method, comprising the following steps: (i) producing the particles, (ii) distributing the particles within the mass of the base material, (iii) forming the layers of the base material with the particles, (iv) exposing said layers to emission, (v) removing the particles from the layers to form the pores, and (vi) producing the porous material from the layers obtained in step (v), said mass of the base material in step (ii) is represented by an optically transparent polymer, and the particles in step (i) are produced from a material having the coefficient of absorption of the emission used in step (iv) higher than that of said base material, wherein in step (iv) said emission is used to heat up the particles and partly evaporate the base material around them so that to make it possible to remove these particles in step (v), and the pores formed after removing the particles are filled with a substance having a refractive index different from the refractive index of the base material. Step (i) involves producing the particles having the diameter d, and in step (iii) the layers of the base material with the particles are preferably formed on substrates by using the centrifugation process and are polymerized, wherein the layer of the base material is formed with the thickness from 0.2d to 1.2d. In step (vi), said porous material is preferably formed by superimposing the layers produced in step (v), using the liquid transfer method. In step (vi), the porous material can be formed in a fixture with spherical inner surface. In step (vi), the porous material can be formed of at least two layers with different concentration of pores, wherein for said layers in step (ii) the particles within the mass of the base material are distributed in different concentrations. In the process, said layers are preferably stacked in such a way that the pore concentration therein increases from one side of the porous material towards the other. In step (i), the particles are preferably produced from a source crystal using the method of femtosecond laser fragmentation or ablation in liquid with the absorption cross-section area S being such that S · I > 10 -7  W, where I is the power density of the emission used in step (iv). After step (vi), the produced porous material is preferably provided with an impermeable outer coating. The produced porous material can be used in contact lens production.
The technical effect, as related to the device, consists in expanding functionality of the porous material by providing increased variability of its optical properties. The set problem has been solved and the technical effect has been achieved by that the porous material having a gradient refractive index, which is implemented as a mass of the base material of optically transparent polymer with the pores distributed therein, is formed by at least two layers with different refractive indices, said layers having pores distributed therein in different concentrations and filled with a substance having a refractive index different from the refractive index of the base material.
 Fig.1
represents the schematic diagram of step (iii) of forming the layers with the particles on substrates by using the centrifugation process;
Fig.2
shows the cross-section of layer 2 with particles 3 in step (iii);
Fig.3
represents the general view of layer 2 with pores 1 formed after removing particles 3 in step (v);
Fig.4
represents the cross-section of layer 2 after removing particles 3;
Fig.5
represents the diagram of step (vi) of producing a flat porous material with an axial refractive index gradient;
Fig.6
represents the diagram of step (vi) of producing a porous material with a radial-spherical refractive index gradient in a fixture with spherical inner surface;
Fig.7
represents a flat porous material with a radial refractive index gradient;
Fig.8
shows the dispersion (the obtained refractive index as a function of the emission wavelength) of the РММА layers with various pore concentrations.
The subject matter of the suggested invention consists in producing an optical material having predetermined properties by means of forming pores 1 within mass 2 of an optically transparent polymer. Said pores can be formed in various concentrations and filled with air or another substance.
To simplify the process of production and enhance controllability of achieving the predetermined optical properties, a porous material producing method is suggested consisting in using high-absorptive particles 3 and implementing the following main steps.
Step (i) of producing the particles.
In the initial step (i), particles 3 having the diameter d (maximum linear dimension) ranging from 10 to 10000 nm are produced from a high-absorptive material by using the method of femtosecond laser fragmentation [Besner, S., Kabashin, A.V., Meunier, Y. «Fragmentation of colloidal nanoparticles by femtosecond laser-induced supercontinuum generation», Appl. Phys. Let. 89(23), 233122, 2006] or ablation [Tselikov, G.I., Ermolaev, G.A., Popov, A.A., Tikhonowski, G.V., Panova, D.A., Taradin, A.S., Vyshnevyy, A.A., Syuy, A.V., Klimentov, S.M., Novikov, S.M., Evlyukhin, A.B., Kabashin, A.V., Arsenin, A.V., Novoselov, K.S., Volkov, V.S. «Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics», PNAS 119(39), e2208830119, 2022] in liquid, e. g. water, alcohol, or acetone. Said methods are reasonably simple and demonstrate good controllability of the process parameters, and, what is most important, high quality of the produced particles 3 with the degree of dispersion varying in a wide range.
In the context of the present invention, high-absorptive material should be understood as a material whose coefficient of absorption of the emission used in step (iv) is higher than that of said base material 2 (polymer) used in step (ii). The target dimension (diameter) of the produced particles 3 is chosen so that the area of the absorption cross-section S meets the condition:
S · I > 10 -7  W,
where I is the power density of the emission used in step (iv).
The most preferable alternatives of said high-absorptive material are nanoclusters of the noble metals such as gold or silver, as well as two-dimensional materials such as molybdenum disulfide, tungsten disulfide, tungsten diselenide, and others.
Laser fragmentation or ablation are carried out using a femtosecond pulse laser. In the process of ablation, the particles are obtained directly from the crystal surface, while in the process of fragmentation – from a mixture of crystalline powder with relatively large crystals and a solvent under constant stirring of the liquid until the target concentration of particles 3 is achieved in the produced solution. This results in producing particles 3 passivated with OH-group and having zeta potential in the range from -50 to -30 mV, enabling their dissolution in a polymer without any additional functionalization (chemical treatment). Diameter d of particles 3 synthesized in this step may vary in the range from 10 to 10000 nm, but preferably is in the range from 1 to 250 nm. The size-selective deposition of particles 3 is carried out using the centrifugation process with the rotation speed increasing from 200 to 8000 rpm, which results in forming monodispersed solutions.
Step (ii) of distributing the particles within the mass of the base material.
The mass of the base material 2 is represented by an optically transparent polymer (vitreous, crystalline, or elastomeric). The most suitable for such application are such polymers as polyvinyl alcohol (PVA, (C2H4O)n), hydroxyethyl methacrylate, polydimethylsiloxane (PDMS, (C2H6OSi)n), polylactide (PLA, (C3H4O2)n), polymethyl methacrylate (PMMA, (C5H8O2)n), polymethylpentene (PMP, (C6H12)n), polycarbonate (PC, (C16H14O3)n) or polyetherimide (PEI, (C37H24O6N2)n), which have the refractive index in the range from 1.3 to 1.8.
Also acceptable are such polymers as polyethylene naphthalate and isomers thereof, such as 2,6-, 1,4-, 1,5-, 2,7- and 2,3-polyethylene naphthalate; polyalkylene terephthalates, such as polyethylene terephthalate, polybutylene terephthalate and poly- 1,4-cyclohexanedimethyleneterephthalate; polyimides, such as polyacrylimides; styrene polymers, such as atactic, isotactic and syndiotactic polystyrene, α-methylpolystyrene, para-methylpolystyrene; polycarbonates, such as bisphenol-A-polycarbonate; poly(meth)acrylates, such as poly(isobutylmethacrylate), poly(propylmethacrylate), poly(ethylmethacrylate), poly(methylmethacrylate), poly(butylacrylate) and poly(methylacrylate) (as used herein, the term "(meth)acrylate" denotes acrylate or methacrylate); cellulose derivatives, such as ethylcellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate and cellulose nitrate; polyalkylene polymers, such as polyethylene, polypropylene, polybutylene, polyisobutylene and poly(4-methyl)pentene; fluorinated polymers, such as perfluoroalkoxy resins, polytetrafluoroethylene, fluorinated copolymers of ethylene and propylene, polyvinylidene fluoride and polychlorotrifluoroethylene and copolymers thereof; chlorinated polymers, such as polydichlorstyrene, polyvinylidene chloride and polyvinyl chloride; polysulfones; polyethersulfones; polyacrylonitrile; polyamides; polyvinylacetate; polyetheramides. Also suitable are such copolymers as styrene-acrylonitrile copolymer, preferably containing 10 to 50 wt%, preferably 20 to 40 wt%, of acrylonitrile, styrene and ethylene copolymer; and poly(ethylene-1, 4-cyclohexylendimethyleneterephthalate). Further polymers include acrylic rubber; isoprene; isobutylene-isoprene; butadiene rubber; butadiene-styrene-vinylpyridine; butyl rubber; polyethylene; chloroprene; epichlorohydrin rubber; ethylene-propylene; ethylene-propylene-diene; nitrile-butadiene; polyisoprene; silicone rubber; styrene-butadiene. Also applicable are bulk-polymerized or grafted copolymers; butadiene-styrene-vinylpyridine; butyl rubber; polyethylene; chloroprene; epichlorohydrin rubber; ethylene-propylene; ethylene-propylene-diene; nitrile-butadiene; polyisoprene; silicone rubber; styrene-butadiene, and urethane rubber.
In order to subsequently produce layers 2 with various optical properties (including the refractive index), particles 3 are distributed within the mass of the base material 2 in various concentrations.
Step (iii) of forming the layers of the base material with the particles.
In this step, the layers of the base material 2 with particles 3 are preferably formed on substrates 4 by using the centrifugation process (spin coating) (Mouhamad Y., Mokarian-Tabari P., Clarke N., Jones R. A. L., and Geoghegan M.«Dynamics of polymer film formation during spin coating», Journal of Applied Physics 116, 123513, 2014). In the process, the base material 2 in the form of liquid polymer with particles 3 having the diameter d is applied on substrate 4 that is rotating at predetermined angular speed and provides the target thickness of polymer layer 2. The layer is formed with the thickness from 0.2d to 1.2d, i.e. not less than 2 nm, but not more than 12000 nm. After that, layer 2 is polymerized using ultraviolet (UV) irradiation.
In another embodiment, layers 2 with required thickness are formed beforehand and then used to place particles 3 therein.
Step (iv) of exposing the formed layers to emission.
In this step (iv), electromagnetic emission having the power density I on the order of 104 W/m2 is used to heat up particles 3 and thereby to partly evaporate base material 2 around them so that to make it possible to remove these particles in the next step. For this purpose, the diameter of the formed pores 1 will be 10–30 % more than the diameter of the used particles 3. Herewith, the maximum achievable size corresponds to approximately 1.3 diameters of the particles due to a rapid drop of the temperature field with the distance from particle 3.
In this step, the size of pores 1 can be varied as well by varying the duration of the emission. Thereby, it is possible to additionally control the effective total volume of pores 1 within the formed layer 2.
Step (v) of removing the particles to form the pores.
In this step, particles 3 are removed from the formed layers 2 by rinsing to produce, as a matter of fact, a polymer film with through holes (pores 1) of the required concentration. Hence, particles 3 can be reused in the next production cycle implementing the suggested method.
Pores 1 formed after removing particles 3 are filled in the current and/or the next step with a substance having the optical properties (refractive index) different from the corresponding properties of the base material 2 (refractive index 1.3–1.8). When filling with air (refractive index 1), the produced layers 2 in the form of a polymer film of the required porosity will have a lower effective refractive index (up to 1.2) than the base material 2 and a low dispersion value (in the range from 0.01 to 0.1 depending on pore concentration, i. e. on the total volume thereof).
Step (vi) of producing a porous material with predetermined optical properties.
In the final step (vi), the target porous material is produced by superimposing the layers obtained in step (v), using the liquid transfer method [R.S. Weatherup, «2D Material Membranes for Operando Atmospheric Pressure Photoelectron Spectroscopy», Topics in Catalysis 61, 2085-2102, 2018]. Said liquid can be water, alcohol, acetone, or a target substance with a different refractive index to fill pores 1 with. If pores 1 are to be filled with liquid, the produced porous material is provided with an impermeable outer coating (encapsulated) in submersed state. If pores 1 are to be filled with air or another gas, the produced material is retrieved and encapsulated in a suitable atmosphere. If filled with air, an impermeable outer coating is not required. The produced target porous material is finally fastened together by natural bonding resulting from the affinity of polymer layers 2, or by means of final polymerization by exposing to UV emission.
The porous material in step (vi) can be produced from at least two layers with different concentrations of pores 1, that is with different optical properties (in particular, the refractive index). To produce a flat porous material with an axial refractive index gradient, said layers 2 are stacked in the thickness direction in such a way that the concentration of pores 1 therein increases from one side of the porous material towards the other . In such a way, when the pores are filled with air, it is possible to produce a porous material in the form of an up to 100 mm thick multilayer polymer sheet having the axial refractive index gradient in the range from 0.01 to 0.6 and a low spectral dispersion value.
When the porous material is formed in fixture 5 with spherical inner surface in an onion-like pattern, the polymer layers 2 with different concentrations of pores 1 varying from one side of the flat porous material towards the other are similarly laid to form a radial-spherical refractive index gradient .
By rolling up a sheet having an axial refractive index gradient into a cylinder (formed by polymer layers 2 with different concentrations of pores 1 varying from the center towards periphery) around a rod with the maximum refractive index (corresponding to the refractive index of base material 2 without pores) and then cutting in a crosswise direction, it is possible to produce flat discs with a defined thickness that have a radial refractive index gradient .
The porous material produced using the disclosed method can be used in contact lens production to form a refractive index gradient or for other purposes.
An independent subject matter of the suggested invention is the porous material having a gradient refractive index, which is implemented as a mass of the base material of optically transparent polymer formed by two or more layers with different refractive indices, said layers having pores 1 distributed therein in different concentrations and filled with a substance having a refractive index different from the refractive index of the base material 2. Such material can be produced using the above described method or any other method that makes it possible to produce it. The common inventive conception of the group of inventions consists in modifying the optical properties of a material by forming pores 1 and filling thereof with a substance having a refractive index different from the refractive index of the base material 2. It should be noted that the substances to fill the nanopores with can be colorants, fluorescent and magnetic substances, etc. Such implementation makes it possible to significantly expand functionality of the porous material by providing increased variability of its optical properties and refractive properties (the refractive index gradient inside the multilayer material can be continuous, discrete or stepwise in any axial, radial or spherical direction, and not necessarily monotonous).
The optical articles corresponding to the suggested group of inventions can provide good intermediate vision, possess the property of accommodation, have high transparency (transmittance up to 99% for the spectral interval in the range of 300–2000 nm), low spectral dispersion value (up to 0.01, which provides significant decrease of chromatic aberrations) and increased refractive index gradient (which, in its turn, makes it possible to expand the field of view up to 200 degrees). In addition, they can provide enhanced water and air permeability, which is critical for wearable optical elements such as a contact lens. In addition, such materials have relatively low cost of production and can be produced in the form of large sheets. Additional control of the optical properties of the material, including the pattern of the refractive index gradient, makes it possible to implement a wide range of gradient lenses, e. g., to correct aberrations, both bifocal and multifocal, with expanded field of view, etc.
The examples below are given to illustrate, but in no way to limit, the suggested method.
Examples
Example 1.
To produce the high-absorptive MoS2 particles in step (i), a femtosecond laser was used having the pulse length of 100 fs, pulse energy of 100 µJ, wavelength of 1030 nm, and recurrence frequency of 10 kHz. In the process of laser ablation, the source MoS2 crystal resided in deionized water, and, using a galvo-scanner, the crystal surface was scanned by a focused laser spot at the scan speed of 1 m/s. The exposure to radiation continued until achieving the final particles concentration of 0.1 mg/ml. Then, using the centrifugation process, from the produced colloidal solution a monodispersed fraction was derived, having the average particles diameter of 100 nm and the dispersion of size distribution not more than 10 %.
In step (ii), the particles were distributed within the base material, for which purpose the obtained solutions having the particle volume content of 0, 5, 10, 15, 20, 25, 30, and 35 % were mechanically mixed in a polymethyl methacrylate polymeric solution.
In step (iii), the produced mixture was exposed to ultrasound and then the centrifugation process (spin coating) was used to form the 100 nm thick layers having the nanoparticle volume content of 0, 5, 10, 15, 20, 25, 30, and 35 %.
In step (iv), each of the layers was exposed to laser irradiation with the wavelength of 633 nm and intensity of 10 kW/cm2, which resulted in evaporation of the polymer around the nanoparticles.
In step (v), the produced films were peeled from the substrates, thereby automatically removing the particles as they were left on the substrate. This resulted in forming the nanopores with the volume concentration of 0, 10, 20, 30, 40, 50, 60, and 70 %, and achieving the effective refractive index of 1.5, 1.45, 1.4, 1.35, 1.3, 1.25, 1.2, and 1.15.
In step (vi), the liquid transfer method was used to transfer the layers one over another to form a multilayer porous polymer sheet.
The transmittance of the produced porous material with the refractive index gradient as measured at the 750 nm wavelength was 99%, while the refractive index dispersion in the range of 300–1000 nm was 0.01.
Example 2.
In step (i), the high-absorptive MoS2 particles were produced similarly to Example 1.
In step (ii), a 100 nm thick layer of polymethyl methacrylate was coated with the MoS2 particles by means of direct application with particle surface coating of 0, 10, 20, 30, 40, 50, 60, and 70%.
The subsequent steps were carried out similarly to Example 1.
The transmittance of the produced porous material with the refractive index gradient as measured at the 750 nm wavelength was 99%, while the refractive index dispersion in the range of 300–1000 nm was 0.01.
Example 3.
Steps (i) – (v) were carried out similarly to Example 1.
In step (vi), the bottom surface of the porous layers of polymethyl methacrylate, having the volume content of pores of 0, 10, 20, 30, 40, 50, 60, and 70%, was coated with a monolayer of graphene. Then, the pores were filled with water, and the second layer of graphene was applied to form thereby an impermeable outer coating. Thereafter, the liquid transfer method was used to transfer the layers one onto another to form a multilayer porous polymer sheet similarly to Example 1, and then onto the inner side of the contact lens.
As a result, the light reflection at the contact lens-to-eye border will decrease to 1 %, as the porous polymer material filled with water will have the refractive index very close to the refractive index of an eye (the difference in refractive indices is less than 0.02). In such a way, the peripheral vision aberrations can be significantly reduced.

Claims (11)

  1. A porous material producing method comprising the following steps:
    (i) producing the particles,
    (ii) distributing the particles within the mass of the base material,
    (iii) forming the layers of the base material with the particles,
    (iv) exposing said layers to emission,
    (v) removing the particles from the layers to form the pores,
    (iv) producing the porous material from the layers obtained in step (v),
    characterized in that
    said mass of the base material in step (ii) is represented by an optically transparent polymer, and the particles in step (i) are produced from a material having the coefficient of absorption of the emission used in step (iv) higher than that of said base material,
    wherein in step (iv) said emission is used to heat up the particles and partly evaporate the base material around them so that to make it possible to remove these particles in step (v),
    and the pores formed after removing the particles are filled with a substance having a refractive index different from the refractive index of the base material.
  2. The method according to claim 1, characterized in that step (i) involves producing the particles having the diameter d, and in step (iii) the layers of the base material with the particles are formed on substrates by using the centrifugation process and are polymerized, wherein the layer of the base material is formed with the thickness from 0.2d to 1.2d.
  3. The method according to claim 2, characterized in that in step (vi) said porous material is formed by superimposing the layers produced in step (v), using the liquid transfer method.
  4. The method according to claim 1, characterized in that in step (vi) the porous material is formed in a fixture with spherical inner surface.
  5. The method according to claim 1, characterized in that in step (vi) the porous material is formed of at least two layers with different concentration of pores, wherein for said layers in step (ii) the particles within the mass of the base material are distributed in different concentrations.
  6. The method according to claim 5, characterized in that while producing the porous material in step (vi) said layers are stacked in such a way that the pore concentration therein increases from one side of the porous material towards the other.
  7. The method according to claim 1, characterized in that in step (i) the particles are produced from a source crystal using the method of femtosecond laser fragmentation or ablation in liquid.
  8. The method according to claim 1, characterized in that in step (i) the particles are produced with the absorption cross-section area S being such that
    S · I > 10-7 W,
    where I is the power density of the emission used in step (iv).
  9. The method according to claim 1, characterized in that after step (vi) the produced porous material is provided with an impermeable outer coating.
  10. A contact lens containing the porous material produced in accordance with the method of claim 1.
  11. A porous material for optical elements with a gradient refractive index, which is implemented as a mass of the base material of optically transparent polymer with the pores distributed therein, characterized in that said porous material is formed by at least two layers with different refractive indices, said layers having pores distributed therein in different concentrations and filled with a substance having a refractive index different from the refractive index of the base material.
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