Method of manufacturing anisotropic porous film from dielectric material

Abstract

A method of manufacturing an anisotropic porous film from a dielectric material and an anisotropic porous film manufactured from a dielectric material (variant embodiments) relate to the field of porous film technology. Arrays of channels are produced by irradiation with accelerated ions, followed by chemical etching. A film is irradiated at at least two set angles α and β to the normal to the surface of the film. In side view, said angles α and β do not lie on the same side of a plane that is perpendicular to the surface of the film and to the primary direction of orientation. In plan view, all of the channels lie in a range of angles no greater than ±10° relative to the primary direction of orientation. In general, several arrays of channels are formed at angles α i and several channels are formed at angles β j and the channels are etched until a diameter d is reached, at which the average number of intersections of a channel of each array by channels of the other arrays is greater than 5. An algorithm for selecting the angles of orientation and other parameters of the channels provides for the formation of a three-dimensional network of pores in the film. The resulting film can be used as an anisotropic porous substrate.

Description

[0001] METHOD FOR PRODUCING AN ANISOTROPIC POROUS FILM FROM A DIELECTRIC MATERIAL

[0002] IPC B 01D 69 / 00

[0003] Field of technology

[0004] The claimed group of inventions relates to the field of technology of porous films made of dielectric materials, in particular polymer porous films, namely porous polymer films with anisotropic properties.

[0005] Prior art

[0006] Porous polymeric materials, particularly films, are in high demand in modern technologies. This is due to their potential for application in many industries to solve a wide variety of scientific and practical problems. Among the wide range of porous systems produced and studied, containing pores ranging from nano- to macroscopic sizes, polymer films are the most promising. They are widely used due to their excellent physical and mechanical properties, flexibility, small thickness, and the availability of feedstock. Various polymers are used to produce porous films, including polyolefins, polyamides, polyurethanes, polyethylene terephthalate, polycarbonate, polyimides, and others. Porous films most often serve as membranes used in liquid and gaseous separation processes, such as microfiltration and ultrafiltration. Another common application for porous films is as separators in power sources.The synthesis of specific nano- and microstructured objects using porous films as matrices has gained particular importance in the last two decades. For this application, the ability to control the architecture of the porous system, particularly the degree of anisotropy and pore size, is crucial.

[0007] One of the most common methods for producing porous polymer films is the solution spinning method, which is particularly developed for the production of ultra- and microfiltration membranes (see Loeb S., Sourirajan S. Adv. Chem. Ser., 38 (1962) 1171 [1]; Mulder M. Introduction to Membrane Technology. Moscow, Mir, 1999, p. 167 [2]). The pore size in such membranes can vary from 10-20 nanometers (ultrafiltration membranes) to micrometers (microfiltration membranes). This method makes it possible to obtain both homogeneous and isotropic porous films, and membranes in which the average pore size varies across the thickness from one side of the film to the other. Such membranes are called asymmetric in the literature, and sometimes also "anisotropic". However, these films (membranes) are isotropic in all directions parallel to the film surface.

[0008] There are inorganic and organic (polymer) films with a porous gradient structure (see Russian Federation Patent No. 2345826 Gas-permeable membrane made of inorganic material. Prior. 13.12.2007, published 10.02.2009. Bulletin No. 4 [3]; Russian Federation Patent 2567907. Method for producing polymer films with a porous gradient structure. Prior. 2014-10-07. Published 2015-11-10. [4]), consisting of several layers that differ in their morphology. The gradient of the properties characterizing the porous structure is directed perpendicular to the surface of the films. These films also do not have longitudinal anisotropy.

[0009] At the same time, there are a number of practical applications for which longitudinal anisotropy of a porous material is a useful property or may become a necessary property in future innovative technical solutions. For example, these include materials for thin-layer chromatography, rapid analytical methods (test strips), and the fabrication of metal-polymer composites with unique electrical and magnetic properties. These applications also require that the scale of the porous structure elements be precisely controlled and that the porous structure be ordered to a certain degree.

[0010] There are porous anisotropic films obtained by molding from a polyethylene or polypropylene melt and subsequent uniaxial or biaxial drawing in air or liquid media. The characteristic pore size in such porous films is fractions of a micrometer. Such films are used, for example, as separators in current sources or membranes for membrane distillation. They have been on the market for many years under the trade name Celgard (see T. Sarada, LC Sawyer, MI Ostler, Three dimensional structure of celgard® microporous membranes, J. Membr. Sci., V.15, Issue 1, 1983, Pages 97-113 [5]; Intern. Application WO2011 / 112885A1. Biaxially oriented porous membranes, composites, and methods of manufacture and use. Filed 11.03.2011, Published 15 September 2011 [6]). The anisotropy of the porous structure is a side effect associated with the production method and does not serve to achieve useful effects, since it cannot be precisely controlled.Methods are known for producing anisotropic porous membranes from polyparaxylylene (see Intern. Application WO 2017 / 132077 Al, Porous articles formed from polyparaxylylene and processes for forming the same, filed 12 January 2017; published 3 August 2017 [7]) and polyamide (see US Patent Application Publication US 2023 / 0347297 Al, Polyamide porous membrane and method for producing the same, filed 24 September 2021, published 2 November 2023 [8]) using combinations of molding techniques that ensure the formation of fibrillar structures with pores elongated in one direction. Such membranes made of polyparaxylylene can be used for filtration, while they have the advantages characteristic of the starting material, i.e. high heat resistance and mechanical strength. In the case of polyamide, the resulting membranes have higher permeability compared to isotropic membranes.Beyond these advantages, no beneficial properties attributable to the anisotropic structure have been reported. The resulting anisotropic structure is characterized by significant pore size variation and heterogeneity.

[0011] A microporous membrane is known, consisting of several anisotropic layers, each of which is composed of parallel-laid fibers, wherein the orientation of the fibers and the packing density of the fibers in adjacent layers are different, as a result of which the resulting membrane has different separation properties in different directions during the movement, for example, of a liquid, in the plane of the membrane (see US Patent 5,139,680, Method for continuous multicomponent separation using anisotropic separation bed. Filed June 5, 1991, Date of patent Aug. 18, 1992 [9]. For this membrane, it is recommended to use as a separation material, capable of separating the components of a mixture during their movement in the volume of the membrane along the surface. In this case, components characterized by different particle sizes move in different preferential directions, thus implementing a two-dimensional chromatographic process.A membrane for filtration of biological fluids, primarily blood, is known, consisting of two or more anisotropic layers, the longitudinal axes of which are rotated relative to each other at angles from 8 to 90° (see US Patent Application US 2008 / 0073294 Al. Porous web, particularly for filtration of biological fluids. Filed Dec. 10, 2004, Pub. Date March 27, 2008

[0010] ). Due to the non-uniform structure of the fiber bundles forming individual layers, the aforementioned membranes are not suitable for applications other than filtration, for example, as a template for the production of anisotropic nano- or microporous structures with a given pore size scale. There is a porous membrane and a method for producing it, which include features close to the claimed technical solution (see Russian Patent 2440840. Porous membrane and a method for producing it. Prior. 10 / 21 / 2009, published 01 / 27 / 2012

[0011] ).The membrane contains at least two arrays of straight, hollow channels with constrictions in the near-surface layer. The channel axes are not parallel, and at least one array consists of blind channels beginning at the surface and terminating deep within the film. These channels are connected by intersections with the channels of the other array, forming a selective layer. The method for producing such a membrane involves irradiating the polymer film with heavy charged particles, such as accelerated ions, some of which have a range shorter than the film thickness, followed by chemical etching. The diameter and length of the pore channels, their inclination angles, and the pore density are selected such that pores belonging to different arrays intersect within the membrane. However, the distinguishing features of this technical solution do not specify the conditions necessary for the porous structure to exhibit anisotropy in a selected direction.

[0012] A heating element is known that is manufactured by filling a system of intersecting cylindrical channels in a polymer film with metal (see Bedin S.A., Kozhina E.P., Panov D.V., Apel P.Yu. Method for manufacturing a film heating element and a film heating element manufactured in this manner. Patent. Russian Federation 2809786, prior. From 11.10.2022, published 18.12.2023, Bull. 25

[0012] ). The base for the film heating element is a polymer film 10-20 μm thick with an array of through intersecting channels with a diameter of 20-2000 nm, a surface density of 10 7 - 10 9 cm -2, characterized by channels arranged at an angle to each other, with the angle ranging from 20 to 150 degrees. The channels form a single porous system, so filling them with an electrically conductive material enables the production of a film heater. The aforementioned polymer film can be considered an analogue, sharing features with the proposed technical solution. However, technical solutions

[0011] and

[0012] do not formulate specific conditions guaranteeing the anisotropy of the porous structure formed by interconnected pores.

[0013] A microporous membrane is known that is obtained by irradiation with particles and chemical etching, leading to the formation of arrays of pores along the trajectories of the particles, wherein the irradiation is carried out on one side and on the other side so that the resulting arrays of cylindrical (or close in shape to a cylinder) pores intersect in the depth of the membrane (see US Patent 4,855,049. Microporous membrane obtained by the irradiation of two faces and process for obtaining the same. Filed Nov. 14, 1988. Date of patent Aug. 8, 1989

[0013] ). In this case, the particles do not penetrate the film completely. This technical solution has features common with the claimed solution, namely: the formation in the membrane of two arrays of cylindrical hollow channels oriented at different angles and, as a result, having mutual intersections, and also the fact that the arrays of the formed channels extend onto at least one surface of the film.The positive effect is achieved by the pore intersections, resulting in a membrane with a smaller proportion of multiple (double, triple, etc.) through-channels penetrating the membrane. This results in superior selectivity compared to a membrane with a conventional structure, i.e., one with straight through-pores. Achieving anisotropic properties in the resulting porous structure is not defined in this technical solution, and the features that ensure this are not established.

[0014] The porous membrane and the method for producing it disclosed in

[0013] are accepted as the closest analogues (prototype) of the claimed group of inventions - a method for producing an anisotropic porous film from a dielectric material and an anisotropic porous film from a dielectric material.

[0015] The essence of the invention

[0016] The technical problem solved by the claimed group of inventions consists of creating a porous polymer film with a controlled degree of anisotropy in a selected direction along the surface of the film.

[0017] In this case, a technical result is achieved, which consists in increasing the homogeneity and degree of anisotropy of the porous structure of the film material.

[0018] The technical problem is solved and the said technical result is achieved by the fact that in a film made of a dielectric material, at least one array of channels is obtained by irradiating the film with ions at a fixed angle α to the normal to the film surface, wherein the angle α is selected in the range greater than 0° and less than 90°; and at least one more array of channels is obtained by irradiating the film with ions at a fixed angle θ to the normal to the said film surface, wherein the angle θ is selected in the range from 0° to 90°; in the horizontal projection, the axes of all channels do not go beyond the range of angles ±10° relative to the preferred direction of orientation, and in the lateral projection, the said angles α and θ do not lie on the same side of the plane perpendicular to the film surface and the preferred direction of orientation.

[0019] In a particular embodiment of the mentioned method, channels are obtained that in horizontal projection are parallel to the preferred direction of orientation.

[0020] In addition, one array of channels is obtained by irradiating the film with ions at a fixed angle α to the normal to the film surface, with the number of ions per unit surface area equal to π, and at least one array of channels is obtained by irradiating the film with ions at a fixed angle π to the normal to the film surface, with the number of ions per unit surface area equal to π. }In the lateral projection, the angles θ and β do not lie on the same side of the plane perpendicular to the film surface and the preferred orientation direction. The channels are etched until a diameter d is reached, which is selected from the condition that the average number of intersections of the channels of the i-th array by the channels of the j-th arrays is greater than 5 and the average number of intersections of the channels of the j-th array by the channels of the i-th arrays Nj is greater than 5, and Aj is calculated using the formulas

[0021] N = 2 d hij nj sin(“i + / ?7) / cos fy,

[0022] N

[0023]

[0024] j = Si 2 d hij n t sin(a z + / ?,) / cos a t ,

[0025] where hy is the thickness of the layer in which the channels of the i-th and j-th arrays intersect, kv l is the total number of the i-th and j-th channel arrays, respectively.

[0026] Two arrays of through channels can be obtained, inclined in the lateral projection in different directions from the plane perpendicular to the film surface and the preferred orientation direction, at angles α and β of equal absolute value, with the number of ions n per unit surface area in both arrays. The channels are etched until a diameter d is reached, which is selected from the condition

[0027] 4 H d p tga > 5,

[0028] where H is the film thickness.

[0029] Two arrays of blind channels are also obtained, exiting onto the same film surface, inclined in lateral projection in different directions from the plane perpendicular to the film surface and the preferred orientation direction, with angles α and β of the same absolute value, with the number of ions n per unit surface area in both arrays. The channels are etched until a diameter d is reached, which is selected from the condition 4 Rdn since > 5,

[0030] where R is the channel length.

[0031] As an embodiment, two arrays of blind channels are obtained, extending onto opposite surfaces of the film, with the number of ions n per unit surface area in both arrays, wherein one array of channels is obtained by irradiating the film with ions from one side at a fixed angle α to the normal to the surface of the film, and another array of channels is obtained by irradiating the film with ions from the opposite side at a fixed angle θ to the normal to the said surface of the film, wherein the angles α and θ are the same in absolute value, wherein the etching of the channels is carried out until the diameter d is reached, which is selected from the condition

[0032] h dn tga > 5,

[0033] where h is the thickness of the layer in which the channels intersect

[0034] By introducing a distinguishing feature that regulates the lower limit of the average number of channel intersections, the anisotropic porous films produced by the proposed method have the most uniform structure. Our experiments have shown that with an average number of intersections of 5 or more, the resulting porous system is most uniform, representing a continuous three-dimensional network and lacking sparse regions, as demonstrated, for example, by liquid impregnation tests or electrical conductivity measurements of the film impregnated with an electrolyte solution.

[0035] This is due to the following reason. The intersection of each channel with other channels is a random process described by the Poisson distribution. For an average number of intersections N, the probability P of encountering a pore with a number of intersections k is described by the following law:

[0036] P(k) = N k exp(-N) / k!

[0037] For an average number of intersections N = 5, the probability of the appearance of a channel that does not intersect with other channels is equal to P(k - 0) « 0.0067 according to the Poisson distribution. The probability of the appearance of a channel with one intersection is equal to P(k = 1) ® 0.034. These channels are not included in the chains that make up a single porous structure and cannot ensure the transport of matter along the porous film in the selected direction. Their total share is only about 4% of the total number of channels, and therefore their presence is practically not a negative factor. With a decrease in the average number of intersections N, the proportion of useless channels increases rapidly. For N = 4, the proportion of such channels is 9%, and for N = 3 their proportion increases to 20%. For an average number of intersections N = 2, the number of useless channels reaches 41%. The presence of these channels worsens the mechanical strength of the film and negatively affects the ability of the porous system to transport matter in the preferred direction of orientation.To ensure transport along a system of interconnected channels over distances of 1 cm or more, the formation of multiple chains composed of fragments of individual channels is necessary. The number of such chains decreases sharply as the percentage of channels not participating in chain formation increases. To achieve a homogeneous porous system, it is preferable for the average number of intersections to be at least 5.

[0038] The above method is used to obtain an anisotropic porous film made of a dielectric material with cylindrical hollow channels belonging to at least two arrays, connected to each other by mutual intersections, and emerging onto at least one surface of the film, wherein in each of the arrays the channels are parallel to each other, in the lateral projection the channels belonging to different arrays are inclined at fixed angles a and p, which do not lie on the same side of the plane perpendicular to the surface of the film and the preferred direction of orientation, wherein the angle a is greater than 0° and less than 90°, and the angle P is greater than or equal to 0° and less than 90°; in the horizontal projection all channels lie in a range of angles no greater than ±10° relative to the preferred direction of orientation.

[0039] As an embodiment, in the horizontal projection all channels are parallel to the preferred direction of orientation.

[0040] As another design option, the channels of all arrays penetrate the film through and through.

[0041] The channels of all arrays can be non-through and exit only onto one surface of the film.

[0042] Also, the channels of all arrays are non-through, and some of them come out on one surface of the film, and the other part comes out on the opposite surface of the film.

[0043] The above anisotropic porous film is made of organic polymer.

[0044] The essence of the proposed invention is illustrated by Figures 1-9. Within the framework of the proposed invention, several specific technical solutions are possible, ensuring the achievement of a beneficial effect. Figures 1-9 illustrate variants of technical solutions.

[0045] The basic principle is illustrated in Figure 1. A film of dielectric material 1 is irradiated with beams of accelerated ions 2 and 3 at angles α and θ to the normal 4 such that the horizontal projections of the ion trajectories in both beams have a direction determined by the line of preferred orientation 5, or deviate from this direction by a limited angle (no more than ±10°). In this case, the angles α and θ lie on opposite sides of plane 6, perpendicular to the film surface and the direction of preferred orientation.

[0046] Let us consider a special case where the channels are parallel to each other in the horizontal projection. Figure 2 shows a structural element of the proposed porous film in horizontal projection. Porous film 1 contains cylindrical channels 7 and 8, the outline of which is shown by dashed lines. Channels inclined at different angles (namely, α and θ) to the surface normal are shown by dashes of different lengths. The axes of the pore channels, shown by dash-dotted lines, are parallel to each other in the horizontal projection. Channels 7 and 8 are localized in space such that the axis of each channel passes through the volume of the other channel. We will call the intersection of channels of this type a direct intersection. Figure 3 shows a different type of intersection, where the axes of channels 7 and 8 do not pass through the volume of the adjacent channel, but the cylindrical surfaces of the channels intersect each other. We will call intersections of this type tangential intersections.Both direct and tangential intersections, when sufficiently concentrated within the film volume, ensure the formation of a unified anisotropic pore system. Accounting for both types of intersections allows us to quantitatively calculate the structural parameters (channel surface density, channel angles, and channel diameter) that yield a unified three-dimensional anisotropic structure. The calculation is based on the principle used to find the mean free path of a particle as it passes through a volume containing stochastically distributed objects (Chen, Frank F. (1984). Introduction to Plasma Physics and Controlled Fusion (1st ed.). Plenum Press, p. 156.).

[0047] Figure 4 shows a side projection of the porous film, showing that channels 7 and 8 are inclined relative to the film surface at angles α and θ, respectively, forming an angle of α + θ with each other. Relative to the surface normal, the projections of channels 7 and 8 are inclined in opposite directions. In practice, achieving perfect parallelism of the channels in the horizontal projection is quite difficult and is not mandatory. To achieve a positive effect, it is sufficient for the channel projections to be parallel to a tolerance that allows the porous structure to exhibit anisotropic properties. When implementing the proposed technical solution by irradiating with heavy ion beams, the trajectories of the ions in the film typically exhibit a natural angular spread of several degrees, which is determined by the conditions of beam transport from the accelerator to the target, as well as ion scattering in the film material. A deviation of the channel axes from parallelism of no more than ±3° is preferred, while a deviation of up to ±10° is acceptable.Moreover, the calculation formulas for the number of intersections give an error of no more than a few percent, which is of little significance in the practical applications of this technical solution.

[0048] A horizontal projection of a porous film with a high pore density is shown in Figure 5. In this case, the pore channels, parallel in the horizontal projection and oriented at different angles in the lateral projection, overlap, indicating their intersection within the film. Forming a unified anisotropic porous system requires a high concentration of channels in intersecting arrays, as shown in Figure 5.

[0049] Two arrays of pore channels, oriented at different angles in the lateral projection, can be placed within the film in different ways, as illustrated in Figures 6-9. Figure 6 demonstrates a variant in which both arrays of pore channels penetrate the film completely. The structure in Figure 7 contains two arrays of non-through channels, entering the film from different sides and not reaching the opposite side of the film. A layer is formed within the film bulk in which channels belonging to different arrays intersect. The structure in Figure 8 contains two arrays of intersecting channels, exiting only on one side of the film. In fact, this structure represents a porous layer monolithically bonded to a non-porous substrate. The following notations are used in the figures: H is the film thickness, h is the thickness of the layer in which the pore channels intersect, R is the length of the cylindrical hollow channel that does not penetrate the film completely.The technical result achieved with this solution is the production of a porous film monolithically bonded to a substrate. The substrate can be significantly thicker than the porous layer, ensuring high mechanical strength, rigidity, and ease of processing (e.g., cutting) of the resulting two-layer material. The angles a and p can be chosen to be equal in absolute value. This option is technologically convenient for implementing the method. Figures 7 and 8 show this embodiment.

[0050] The number of pore channel arrays, each with channels parallel to one another, with the channel axes of all arrays parallel to one another in horizontal projection, can be greater than two. For example, Figure 9 shows a side projection of a structure containing four pore channel arrays, two of which are inclined in one direction from the vertical axis (sc, ag), and the other two in the opposite direction (pi, r). Similarly, the number of pore arrays in the structures shown in Figures 7 and 8 can be greater than two. The number of arrays is limited from above by the number of ions: in the limit, each array can consist of the track of a single ion, characterized by its own individual angle.

[0051] As an extreme option, one of the angles can be zero, as shown in Figure 10. Since the other angle is nonzero, the axes of the channels belonging to the two arrays intersect and form a single porous structure with anisotropic properties. This option is also convenient for practical implementation, since perpendicular ion irradiation is technically the simplest.

[0052] The quality of the resulting anisotropic porous film, primarily the degree of anisotropy, depends on the angle(s) between the arrays of intersecting channels. It is preferable for the sum of the angles αc + β to be at least 30°. At smaller angles, the degree of anisotropy is low. Excessively large angles, greater than 150°, are also undesirable, as they cause the opposing channels to merge over long sections when they intersect, and the resulting structure is characterized by significant structural inhomogeneities. However, it is impossible to precisely define the optimal range of angles, since the properties of the resulting structure also depend on other parameters, namely, pore density, pore diameter, and structure thickness. Therefore, a more precise criterion is the number of intersections per channel, the lower limit of which is specified in this technical solution. The upper limit for the number of intersections is not specified.

[0053] The anisotropic porous films claimed by this technical solution possess a porous structure whose properties vary in different directions. Specifically, there is a preferred direction for substance transport during impregnation and diffusion, as well as a preferred direction for the movement of electrical charges when the pore channels are filled with a conductive material. This direction is a key property of the claimed porous film and is designated in this description by the term "preferred orientation direction." Furthermore, the structure is highly uniform, and the desired pore channel size can be specified.

[0054] Brief description of the drawings

[0055] Figure 1 is a general diagram of the proposed method for creating an anisotropic porous film.

[0056] 1 - initial film of dielectric material;

[0057] 2 — the direction of incidence of the ion beam, which determines the direction of the array of pore channels, at an angle a;

[0058] 3 - the direction of incidence of the ion beam, which determines the direction of the array of pore channels, at angle P;

[0059] 4 - normal to the film surface;

[0060] 5 - preferred orientation direction; the thin dashed lines show the permissible deviation from parallelism to the preferred orientation direction.

[0061] 6 - plane perpendicular to the preferred direction of orientation and the surface of the film.

[0062] Figure 2 is a horizontal projection drawing of film 1 with two intersecting through-hole cylindrical channels 7 and 8. The channels form a direct intersection, characterized by the axis of each channel penetrating the volume of the other channel. The channel projections are oriented along the preferred orientation direction 5.

[0063] Figure 3 is a horizontal projection drawing of film 1 with two intersecting through-hole cylindrical channels 7 and 8. The channels form a tangential intersection, characterized by the channel axes not passing through the volume of the other channel. The channel projections are oriented along the preferred orientation direction 5.

[0064] Figure 4 is a side projection drawing of film 1 with a pair of intersecting through-hole cylindrical channels 7 and 8. Figure 5 is a horizontal projection drawing of film 1 with a larger number of intersecting through-hole cylindrical channels. For example, two channels (7 and 8) are shown intersecting each other and simultaneously intersecting with other channels. The channel projections are oriented along the preferred orientation direction 5.

[0065] Figure 6 is a side projection of film 1 with thickness H with two arrays of through channels inclined in different directions relative to the normal to the film surface at angles α and β. Positions 7 and 8 correspond to channels from the two mentioned arrays.

[0066] Figure 7 is a side projection of film 1 with two arrays of blind cylindrical channels that exit on opposite film surfaces and are inclined in opposite directions relative to the film surface normal. The absolute value of angle θ is equal to angle α. h is the thickness of the layer in which the pore channels intersect, and R is the length of the cylindrical hollow channel that does not completely penetrate the film. Positions 7 and 8 correspond to channels from the two aforementioned arrays.

[0067] Figure 8 is a side projection of film 1 with two arrays of blind cylindrical channels that exit onto the same film surface and are inclined in opposite directions relative to the normal to the film surface of thickness H, with the angle 0 equal in absolute value to the angle a; h is the thickness of the layer in which the pore channels intersect, and R is the length of the cylindrical hollow channel that does not completely penetrate the film. Positions 7 and 8 correspond to channels from the two aforementioned arrays.

[0068] Figure 9 is a side projection of film 1 with four arrays of through cylindrical channels, two of which are inclined in one direction relative to the normal to the film surface (angles a1 and ar) and the other two are inclined in the other direction relative to the normal to the film surface (angles 01 and 0r). Positions 7 and 7' designate channels from arrays oriented at angles 01 and 02, positions 8 and 8' correspond to channels from arrays oriented at angles a1 and ar, respectively.

[0069] Figure 10 is a side view of film 1 with two arrays of through cylindrical channels, one of which is perpendicular to the film surface (0 = 0), and the other, a, is inclined to the left of the plane perpendicular to the preferred orientation direction and the film surface. Figure 11 is an electron micrograph of a film section with two arrays of through cylindrical channels intersecting at an angle of 87°. The section is made along the preferred orientation direction and perpendicular to the film surface.

[0070] Figure 12 is an electron micrograph of a film section with two arrays of through-hole cylindrical channels intersecting at an angle of 40°. The section is taken along the preferred orientation direction and perpendicular to the film surface.

[0071] Figure 13 is an electron micrograph of the surface (left) and a section of the film (right) with two arrays of blind cylindrical channels intersecting at an angle of 135°.

[0072] Figure 14 is a series of optical photographs demonstrating the dynamics of water impregnation of an anisotropic porous film. The time between the first and last exposures is 60 seconds.

[0073] Implementation of the invention

[0074] The claimed method is implemented as follows.

[0075] A polymer film, such as polyethylene terephthalate (PET), polycarbonate (PC), polyimide (PI), or another polymer, is irradiated with a beam of accelerated ions directed at an angle α relative to the film surface normal. The film is rotated and irradiated with a beam of accelerated ions at an angle θ to the film surface normal, orienting it so that the ion track projections in the horizontal projection of the film are parallel. The irradiation time and ion beam intensity are set to achieve the desired fluence values ​​in each array. If necessary, the procedure is repeated, producing more than two arrays of ion tracks in the film at different angles θt and θj.

[0076] Accelerated ions, passing through the polymer, leave extended defects called tracks. In the cases shown in Figures 4 and 6, ions with an energy sufficient to pass through the film were used. The tracks penetrate the film from one side to the other. Figures 7 and 8 illustrate the situation where the ion range R is chosen to create arrays of blind tracks in the film at the required angles. In the case of Fig. 7, the film is irradiated from different sides, producing arrays of tracks intersecting within the film. The thickness of the layer in which the tracks intersect is h, which can be controlled by varying the ion energy (and thus the range R), as well as by selecting the film thickness and the ion entry angles. In the case of Fig. 8 The film is irradiated from one side in such a way that the layer containing the intersecting tracks is adjacent to one side of the film, and the layer of the original (not exposed to ions) material is adjacent to the back side of the film.

[0077] Heavy ion tracks exhibit selective etching properties. Using solutions of appropriate reagents, ion tracks are converted into hollow channels by selective etching. Optimal etching solution compositions exist for each polymer. The solution composition, etching temperature, and etching duration are the parameters used to set the required channel diameter d. Using this technology, the channel diameter can be set in the range from 10 nm to tens of micrometers [see Apel, P. Yu. 2013. Track-Etching. In: Encyclopedia of Membrane Science and Technology. John Wiley and Sons, 1-25; doi: 10.1002 / 9781118522318

[0014] ). The channel diameter can be conveniently adjusted by setting the etching time while holding other parameters (temperature and solution concentration) constant.

[0078] A convenient and simple option for implementing the method is to create only two arrays of pore channels with identical ion fluences n and identical absolute film entry angles a and p, but lying on opposite sides of the surface normal in the lateral projection. This significantly simplifies both the calculation of the required parameters (the two conditions included in the invention formula are reduced to one) and the practical implementation. The two ion irradiation operations are identical, and it is only necessary to rotate the irradiated film 180 degrees before the second operation. The average number of intersections of the channels of one array with the channels of the other array, N, is the same for both arrays and is calculated using the formula

[0079] N= 4 R dn since,

[0080] where R is the channel length. This approach is convenient for creating a porous layer on a nonporous substrate. In this case, the ion energy is chosen such that the ion range R satisfies the condition R coscc < H, as shown in Figure 8.

[0081] When choosing the ion range and ion entry angles such that the condition J?-cosa > H is satisfied, the ions penetrate the film through and through, and in this case the average number of intersections N is found from

[0082] N= Hdn tga. Another easily implemented and practically useful option is a structure formed by two arrays of blind pores, illustrated in Figure 7, for which the average number of intersections N is found from

[0083] N= 4 h dn tgoc,

[0084] where h is the thickness of the intersection layer.

[0085] The anisotropic properties of the porous films obtained according to the claimed technical solution can be quantitatively characterized by various experimental methods, for example, by measuring the impregnation rate of wetting liquids in different directions, as well as by measuring the electrical conductivity of porous films impregnated with electrolyte solutions, also in different directions.

[0086] The possibility of implementing the claimed method is confirmed by examples.

[0087] Example 1. A polyethylene terephthalate (PET) film 23 µm thick, 320 mm wide and 2 m long was irradiated with a beam of accelerated krypton ions with an energy of 250 MeV, transporting the film at a constant speed, at an angle of 43.5° to the beam, so that the surface density of ion tracks was 5x10 7 cm -2. During irradiation, the ions penetrated the film completely. Then the film was turned over and irradiated again, transporting the film under the same conditions. The ion-irradiated film was exposed for 60 minutes in air with LE-30 UV lamps to sensitize the tracks. The film was treated in IM NaOH at 70° for 30 minutes. The resulting porous film was examined in a scanning electron microscope. A longitudinal section of the film is shown in Figure 11. The channel diameter was 0.3 μm. Effective intersection of the pore channels of both arrays was achieved due to the fact that the value of the parameter N = 4 L d n since, was 13.5 (this value is the sum of the values ​​L = 32.5x10' 4 cm, d= O.ZxY' 4 cm, n = 5x10 7 cm -2, sin a = 0.69). Samples measuring 10 x 3 cm were cut from the resulting porous film in two mutually perpendicular directions, and the impregnation rate with a non-evaporating liquid, namely pentadecane, was measured. The impregnation rate in the longitudinal direction was five times higher than the impregnation rate in the transverse direction.

[0088] Example 2. A polyethylene terephthalate (PET) film 23 μm thick, 320 mm wide and 2 m long was irradiated with a beam of accelerated krypton ions with an energy of 250 MeV, transporting the film at a constant speed, at an angle of 20° between the beam and the normal to the film surface, so that the surface density of ion tracks was 6x10 7 cm" 2. During irradiation, the ions pierced the film through and through. Then the film was turned over and irradiated again, transporting the film under the same conditions and ensuring parallel orientation of the projections of the ion trajectories during the first and repeated irradiation. The ion-irradiated film was exposed for 60 minutes in air with LE-30 UV lamps to sensitize the tracks. The film was immersed in IM NaOH and treated at 70° for 38 minutes. The resulting porous film was examined in a scanning electron microscope. A longitudinal section of the film is shown in Figure 12. The diameter of the channels was 0.4 μm. Effective intersection of the pore channels of both arrays was achieved due to the fact that the value of the parameter N = 4 L dn since, was 8.0 (this value is the sum of the values ​​L = 24.5x10' 4 cm, d= 0.4x10' 4 cm, n = 6x10 7 cm -2, since = 0.342). Samples measuring 10 x 3 cm were cut from the resulting porous film in two mutually perpendicular directions, and the pentadecane impregnation rate was measured. The impregnation rate in the longitudinal direction was four times higher than the impregnation rate in the transverse direction.

[0089] Example 3. A polyethylene terephthalate (PET) film 30 μm thick, 320 mm wide and 2 m long was irradiated with a beam of accelerated xenon ions with an energy of 160 MeV at an angle of 66° between the beam and the normal to the film surface, transporting the film at a constant speed so that the ion track density was 7x10 6 cm -2The ion range in the polymer was R = 20 μm, and the ions penetrated the film to a depth of 8 μm. The film was then inverted and irradiated again, transporting the film under the same conditions and ensuring parallel orientation of the ion trajectory projections during the first and repeated irradiation. The ion-irradiated film was exposed for 60 min in air under LE-30 UV lamps to sensitize the tracks. The film was immersed in 6 M NaOH and treated at 70° for 25 min. The resulting porous film was examined under a scanning electron microscope. The film surface and a longitudinal section through the film are shown in Figure 13. The channel diameter was 1 μm. The top layer, approximately 8 μm thick, contains intersecting channels. Below is a nonporous monolithic layer approximately 20 μm thick. The effective intersection of the pore channels of both arrays was achieved due to the fact that the value of the parameter N = 4 L d n sina was 5.1 (this number is obtained from the values ​​L = 20x10' 4 cm, d = 1x10' 4 cm, n = 7x106 cm -2 , sin a = 0.91). Samples measuring 5 x 5 cm were cut from the resulting porous film, and the dynamics of its impregnation with a wetting liquid were studied. Figure 14 illustrates the anisotropic properties of the porous film with respect to water impregnation. The successive stages of the development of a water-impregnated spot, recorded during the first 60 seconds after drop application, are shown. The horizontal direction in the figure corresponds to the preferred orientation direction of the horizontal projections of the pore channels in the film. The difference in the liquid front propagation velocities in the longitudinal and transverse directions (the degree of anisotropy) reaches 10.

[0090] Example 4. A polyethylene terephthalate (PET) film 12 µm thick, 320 mm wide and 2 m long was irradiated with a beam of accelerated xenon ions with an energy of 160 MeV, transporting the film at a constant speed at an angle of η - 30° between the beam and the normal to the film surface, so that the ion track density was n1 = 6x10 7 cm -2 During irradiation, the ions penetrated the film completely. The angle between the ion beam direction and the film surface was then set to αβ = 45°, and the irradiation was repeated, increasing the total track density by m = 6x10 7 cm -2 The film was inverted and subjected to two irradiations under the same conditions, ensuring parallel orientation of the horizontal projections of the ion trajectories in all four operations. Four track arrays were obtained, each characterized by the same surface track density щ = п = п. The film was treated in IM NaOH at 70°C for 30 minutes. The channel diameter d was 0.3 µm.

[0091] The average number of intersections of the channels of the first array (i=l) by the channels of two opposite arrays (j = 1, 2) is found from the ratio

[0092] JV(i=l) = 2 h dn sin (ai + Pi) / cosai + 2 hdn sin (ai + 2) / cosai =

[0093] (Z h dn / cosai) x [sin (ai + Pi) + sin (ai + pg)]

[0094] The average number of intersections of the channels of the second array (i=2) by the channels of two opposing arrays (j = l, 2) is found from the ratio

[0095] jV(i=2) = 2 hd n sin (ag + Pi) / coz + 2 hdn sin (a2 + P2) / cosai =

[0096] (2 h dn / cosai) x [sin (ar + Pi) + sin (ar + Pr)]

[0097] The values ​​of 2V(i=l) and 7V(i=2) were 9.1 and 12.0, respectively. Due to the symmetry of the structure, the number of channel intersections in two opposing arrays (j=l) and j=2) are calculated using a similar algorithm and take the same values ​​of 9.1 and 12.0, which ensured the formation of a single anisotropic porous structure. A test of water drop spreading in the volume of the film showed a degree of anisotropy equal to ~ 3. Samples measuring 1x5 cm in the longitudinal and transverse directions were cut from the film and impregnated with an electrolyte solution with a specific conductivity of 1.6 mS cm 1 Flat platinum electrodes were connected to the ends of the samples, and the electrical resistance was measured with alternating current at a frequency of 1 kHz. In the longitudinal direction, the resistance of the sample was 3.0-10 6 Ohm, and in the transverse - 11-U 60m. Example 5. A polyethylene terephthalate (PET) film 23 μm thick, 320 mm wide and 2 m long was irradiated with a beam of accelerated xenon ions with an energy of 160 MeV, transporting the film at a constant speed at an angle of oil = 43° between the beam and the normal to the film surface, so that the ion track density was 1x10 8 cm -2 The ion range in the polymer was R = 20 μm, and the ions penetrated the film to a depth of approximately 15 μm. The film was then inverted and irradiated again, transporting the film under the same conditions and ensuring parallel orientation of the ion trajectories in the horizontal projection during the first and second irradiations. The film was treated with a 1M NaOH solution at 70°C for 54 min until a pore diameter of 0.56 μm was achieved. A three-layer porous structure with a channel intersection layer thickness of 7 μm was obtained. Testing with pentadecane showed that the ratio of the impregnation rates in the longitudinal and transverse directions was 2.5.

[0098] Example 6. A sample of polycarbonate film with a thickness of 175 µm and dimensions of 5 x 7 cm was irradiated with a beam of accelerated bismuth ions with an energy of 700 MeV at an angle of 30° between the beam and the normal to the film surface, so that the ion track density was 2.5 x 10 7 cm -2 The ion range in the polymer was R = 50 μm, and the ions penetrated the film to a depth of approximately 43 μm. The film was then inverted and irradiated again, transporting the film under the same conditions and ensuring parallel orientation of the ion trajectories in the horizontal projection during the first and second irradiations. The film was treated with a 1M NaOH solution at 70°C for 70 min until a pore diameter of 1 μm was achieved. An anisotropic porous film was obtained in which the layer penetrated by intersecting channels has a thickness of 43 μm, and this layer is monolithically bonded to a nonporous substrate 132 μm thick.

[0099] Thus, the presented materials demonstrate that the proposed technical solution enables the production of anisotropic porous polymer films with controlled properties and a predetermined direction of the preferred orientation of the interconnected pore system. The described anisotropic porous films can be used as impregnated porous substrates in rapid analysis methods, as substrates for thin-layer chromatography, as matrices for growing anisotropic metallic nano- and microstructures, and in nano- and microfluidic devices requiring anisotropic substance transport.

Claims

CLAUSES OF THE INVENTION Item 1. A method for producing an anisotropic porous film from a dielectric material, comprising irradiation with accelerated ions at several angles and subsequent chemical etching to form hollow channels connected to each other by mutual intersections, along the trajectories of the said ions, characterized in that at least one array of channels is obtained by irradiating the film with ions at a fixed angle a to the normal to the film surface, wherein the angle a is selected in the range greater than 0° and less than 90°; and at least one more array of channels is obtained by irradiating the film with ions at a fixed angle P to the normal to the said film surface, wherein the angle P is selected in the range from 0° to 90°;in the horizontal projection, the axes of all channels do not go beyond the range of angles of ±10° relative to the preferred direction of orientation, and in the lateral projection, the mentioned angles a and P do not lie on the same side of the plane perpendicular to the surface of the film and the preferred direction of orientation. Item 2. The method according to item 1, characterized in that channels are obtained that in horizontal projection are parallel to the preferred direction of orientation. Item 3. The method according to items 1 and 2, characterized in that at least one array of channels is obtained by irradiating the film with ions at a fixed angle a; to the normal to the surface of the film, with the number of ions per unit surface area equal to nj, and at least one array of channels is obtained by irradiating the film with ions at a fixed angle p; to the normal to the said surface of the film, with the number of ions per unit surface area equal to nj, wherein the etching of the channels is carried out until a diameter d is reached, which is selected from the condition that the average number of intersections of the channels of the i-th array by the channels of the j-th arrays N is greater than 5 and the average number of intersections of the channels of the j -th array by the channels of the i-th arrays JVj is greater than 5, wherein N and Aj are calculated using the formulas M = Si 2 d htj nj sin(a £ + / ?7) / cos Pj, N j = 2 dh t j nt sin(a £ + / ?;) / cos a t , where hy is the thickness of the layer in which the channels of the i-th and j-th arrays intersect, kvi l is the total number of the i-th and j-th channel arrays, respectively. Item 4. The method according to items 1 and 2, characterized in that two arrays of through channels are obtained, inclined in the lateral projection to the same absolute the magnitude of the angles a and, with the number of ions n per unit surface area in both arrays, while the etching of the channels is carried out until the diameter d is reached, which is selected from the condition 4 H dn tga > 5, where H is the film thickness. Item 5. The method according to paragraphs 1 and 2, characterized in that two arrays of blind channels are obtained, emerging on the same surface of the film, inclined in the lateral projection at angles α and θ of the same absolute value, with the number of ions n per unit surface area in both arrays, while the etching of the channels is carried out until the diameter d is reached, which is selected from the condition 4 R dn sina > 5, where R is the channel length. Item 6. The method according to items 1 and 2, characterized in that two arrays of blind channels are obtained, emerging on opposite surfaces of the film, with the number of ions n per unit surface area in both arrays, wherein one array of channels is obtained by irradiating the film with ions from one side at a fixed angle α to the normal to the surface of the film, and another array of channels is obtained by irradiating the film with ions from the opposite side at a fixed angle θ to the normal to the said surface of the film, wherein the angles α and θ are the same in absolute value, wherein the etching of the channels is carried out until the diameter d is reached, which is selected from the condition ^ h dn tga > 5, where h is the thickness of the layer in which the channels intersect Item 7. An anisotropic porous film made of a dielectric material containing cylindrical hollow channels belonging to at least two arrays, connected to each other by mutual intersections, and extending onto at least one surface of the film, characterized in that in each of the arrays the channels are parallel to each other, in the lateral projection the channels belonging to different arrays are inclined at fixed angles a and 0, which do not lie on the same side of the plane perpendicular to the surface of the film and the preferred direction of orientation, wherein the angle a is greater than 0° and less than 90°, and the angle 0 is greater than or equal to 0° and less than 90°; In the horizontal projection, all channels lie within an angle range of no more than ±10° relative to the preferred orientation direction. Item 8. An anisotropic porous film made of a dielectric material according to item 7, characterized in that in the horizontal projection all channels are parallel to the preferred direction of orientation. Item 9. An anisotropic porous film made of a dielectric material according to Item 7-8, characterized in that the channels of all arrays penetrate the film through and through. Item 10. An anisotropic porous film made of a dielectric material according to Item 7-8, characterized in that the channels of all arrays are non-through and extend only to one surface of the film. Item 11. An anisotropic porous film made of a dielectric material according to items 7-8, characterized in that the channels of all arrays are non-through, and some of them exit onto one surface of the film, while the other part exits onto the opposite surface of the film. Item 12. An anisotropic porous film according to paragraphs 7-8, characterized in that the film is made of an organic polymer.

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