PROCESS FOR MANUFACTURING A MULTILAYER MEMBRANE ON A SOLID SUPPORT USING AN AMPHIPHILIC BLOCK COPOLYMER

Abstract

Disclosed is a process for manufacturing a membrane from a, amphiphilic block copolymer including a hydrophilic block and a hydrophobic block including functions capable of forming a bond with the hydrophilic block in a bath containing the copolymer in solution in an apolar organic solvent, for a sufficient time to enable the formation of non-covalent bonds between the hydrophilic block and the support and the immobilisation of a first layer of the copolymer on the surface of the support; followed by adding water to the bath, so as to give rise to the self-assembly of a second layer of copolymer on the first layer.

Claims

1. Method for manufacturing a membrane from at least one amphiphilic block copolymer, referred to as the first amphiphilic block copolymer, comprising at least one hydrophilic block and at least one hydrophobic block, said method comprising successive steps of: a) immersing a support comprising functions able to form a bond with said hydrophilic block in a first bath containing said first amphiphilic block copolymer in solution in an organic solvent in which said hydrophilic block and said hydrophobic block are soluble, for a sufficient period to enable the formation of bonds between said hydrophilic block and said support, and the immobilisation of a first layer of said first amphiphilic block copolymer on the surface of said support; b) when appropriate, replacing said first bath with a second bath containing a second amphiphilic block copolymer comprising at least one hydrophilic block and at least one hydrophobic block, in solution in an organic solvent in which the hydrophilic block and the hydrophobic block of the second amphiphilic block copolymer are soluble; c) and adding water to the bath containing said support on the surface of which said first layer is immobilised, the addition of water causing the self-assembly of a second layer of amphiphilic block copolymer on said first layer.

2. Method according to claim 1, comprising, after the step c) of adding water to the bath, a step d) of rinsing the support and layers of amphiphilic block copolymer with an aqueous solution.

3. Method according to claim 2, wherein the rinsing step d) comprises the gradual replacement of the organic solvent contained in the bath with water.

4. Method according to claim 1, wherein the step c) of adding water to the bath comprises the gradual introduction of a liquid aqueous solution in said bath.

5. Method according to claim 4, wherein the gradual introduction of a liquid aqueous solution in the bath is carried out at a rate making it possible to obtain an increase in the quantity of water in the bath of less than or equal to 50% by volume, with respect to the total volume of the bath, per minute.

6. Method according to claim 4, wherein the gradual introduction of a liquid aqueous solution in the bath is carried out until a quantity of water is obtained in the bath of between 5% and 50% by volume with respect to the total volume of the bath.

7. Method according to claim 1, wherein step c) of adding water to the bath comprises putting the bath in contact with saturated water vapour.

8. Method according to claim 7, wherein putting the bath in contact with saturated water vapour is carried out for a period of between 10 and 180 minutes.

9. Method according to claim 1, wherein step a) of immersing the support in the first bath is carried out for a period of between 10 and 180 minutes.

10. Method according to claim 1, wherein the first bath contains said first amphiphilic block copolymer at a concentration of between 0.01 and 10 g/l in said organic solvent.

11. Method according to claim 1, wherein the second bath contains said second amphiphilic block copolymer at a concentration of between 0.01 and 10 g/l in said organic solvent.

12. Method according to claim 1, wherein the first amphiphilic block copolymer (20), and when appropriate the second amphiphilic block copolymer, is a diblock copolymer or a triblock copolymer.

13. Method according to claim 1, wherein the hydrophobic block of the first amphiphilic block copolymer, and when appropriate of the second amphiphilic block copolymer, is chosen from the group consisting of hydrophobic polystyrenes, polyacrylates, polydienes, polylactones, polylactides, polyglycolides, polyolefins, polyoxiranes, polysiloxanes, polyacrylonitriles, vinyl polyacetates, polytetrahydrofuran, polyhydroxyalkanoates, polythiophenes, hydrophobic polypeptides, and polycarbonates.

14. Method according to claim 1, wherein the hydrophilic block of the first amphiphilic block copolymer, and when appropriate the hydrophilic block of the second amphiphilic block copolymer, is chosen from the group consisting of polyacrylic acids, polyacrylamides, polyethers, polystyrene sulfonic acids, polyvinyl alcohols, poly(2-vinyl N-methyl pyridinium), poly(4-vinyl N-methyl pyridinium), polyamines, hydrophilic polypeptides, polyoxazolines, polysaccharides, polyureas, zwitterionic polymers, or any of the salts thereof.

15. Method according to claim 1, wherein the organic solvent of the first bath, and when appropriate the organic solvent of the second bath, is chosen from the group consisting of tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, acetonitrile, dioxane, acetone, ethylene glycol, methanol, pyridine, N-methyl-2-pyrrolidone, toluene, dichloromethane, chloroform, xylene, hexafluoroisopropanol, or any of the mixtures thereof.

16. Method according to claim 1, wherein the support is formed from a material chosen from the group consisting of ceramics, glasses, silicates, polymers, graphite and metals.

17. Membrane obtainable by a method according to claim 1, comprising a first layer of an amphiphilic block copolymer immobilised on a support, and a second layer of an amphiphilic block copolymer fixed to said first layer by hydrophobic interaction.

18. Method according to claim 2, wherein the step c) of adding water to the bath comprises the gradual introduction of a liquid aqueous solution in said bath.

19. Method according to claim 3, wherein the step c) of adding water to the bath comprises the gradual introduction of a liquid aqueous solution in said bath.

20. Method according to claim 5, wherein the gradual introduction of a liquid aqueous solution in the bath is carried out until a quantity of water is obtained in the bath of between 5% and 50% by volume with respect to the total volume of the bath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0111] The features and advantages of the invention will emerge more clearly in the light of the example embodiments below, provided simply for illustration and in no way limitatively of the invention, with the support of FIGS. 1 to 7, in which:

[0112] FIG. 1 shows schematically the various steps of manufacturing a dual-layer membrane from an amphiphilic block copolymer by the use of a method according to the invention;

[0113] FIG. 2 shows the results obtained for the analysis of a monolayer of PS-b-PAA formed in accordance with the invention on a silicon support, a) by quartz crystal microbalance with dissipation, in the form of a graph showing the quantity of copolymer adsorbed according to the concentration of copolymer in the first bath; b) by atomic force microscopy (AFM); c) in the form of a graph showing the distribution of the heights determined using AFM analysis;

[0114] FIG. 3 shows the results obtained for the analysis of a symmetrical dual layer of PS-b-PAA formed in accordance with the invention on a silicon support, a) by quartz crystal microbalance with dissipation, in the form of a graph showing the quantity of copolymer adsorbed as a function of the reaction time; b) by atomic force microscopy (AFM); FIG. 3a) shows schematically the solid support and the layer or layers of copolymer immobilised on its surface, for each step of the method and the corresponding reaction time;

[0115] FIG. 4 shows atomic force microscopy images of a monolayer of PS-b-POE formed in accordance with the invention on a silicon support, a) 55 m.sup.2, b) 11 m.sup.2;

[0116] FIG. 5 shows the results obtained for the analysis of an asymmetric dual layer PS-b-PAA and PS-b-POE formed in accordance with the invention on a silicon support, a) by atomic force microscopy (AFM); b) in the form of a graph showing the distribution of the heights obtained using AFM analysis;

[0117] FIG. 6 shows schematically a dual-layer membrane encapsulating nanoparticles, obtained from an amphiphilic block copolymer by the use of a method according to the invention;

[0118] FIG. 7 shows spectra obtained by transmission UV-visible spectroscopy, respectively for a dual-layer membrane encapsulating gold nanoparticles obtained by a method according to the present invention (continuous curve) and for gold nanoparticles in solution in a mixture of tetrahydrofuran and dimethylformamide (broken-line curve).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0119] The various steps for forming, on a solid support 10, a dual-layer membrane based on an amphiphilic block copolymer 20, by implementing a method according to the present invention, are illustrated schematically in FIG. 1.

[0120] In the embodiment shown in this figure, the solid support is a flat plate. The method according to the invention is advantageously applicable in a similar manner to supports of any other form.

[0121] The solid support 10 carries on its surface functions able to form bonds with the amphiphilic block copolymer 20. In the following description, the example of non-covalent bonds will be taken, this naturally being in no way limitative of the invention.

[0122] In a first step a), the solid support 10 is immersed in a bath 11 comprising an amphiphilic block copolymer 20 in solution in an organic solvent.

[0123] The amphiphilic block copolymer 20 comprises at least one hydrophilic block 21 and at least one hydrophobic block 22. In the particular embodiment illustrated in FIG. 1, it is a diblock copolymer comprising one hydrophilic block and one hydrophobic block. The invention applies in a similar manner to any other type of block copolymer, in particular, but non-limitatively, to triblock copolymers.

[0124] The solvent used is a solvent with a polarity lower than that of water, non-selective for the copolymer, in which the two blocks are well solvated, or a mixture of solvents having such properties.

[0125] Putting the solid 10 in contact with the bath 11 of copolymer 20, under such conditions, gives rise, as illustrated at 30 in FIG. 1, at step al), to the formation of non-covalent bonds between the solid support 10 and the hydrophilic block 21 of the copolymer. In this way a monolayer formed from hydrophilic blocks 21 is formed on the solid support 10. The hydrophobic blocks 22 for their part extend from this monolayer, probably in a comb configuration.

[0126] A few copolymer molecules 20 remain free in solution.

[0127] As illustrated at 31 in FIG. 1, in the following step c), water is added to the bath 11.

[0128] When the solvent used is a water-miscible solvent, this is achieved by the gradual addition of a liquid aqueous solution to the bath 11, as indicated at 13 in FIG. 1. The addition is preferably carried out under conditions as close as possible to pseudo-equilibrium conditions. Thus the aqueous solution is preferably added very gently, at a rate of a few hundreds of microlitres per minute, and in a region of the reservoir 12 containing the bath 11 and the solid support 10 remote from the latter, so as to obtain in the reservoir 12 an almost horizontal diffusion of the water.

[0129] When the solvent used is a solvent that is not miscible with water, the bath 11 is put in the presence of saturated water vapour.

[0130] Whatever the method employed, this putting of the bath 11 in contact with the water gives rise to a gradual change in the polarity of the bath, which triggers the self-assembly of a second layer of copolymer on the monolayer fixed to the solid support 10. More precisely, the hydrophobic blocks 22 of the copolymer molecules free in the bath 11 assemble on the hydrophobic blocks 22 of the copolymer molecules constituting the monolayer fixed to the solid support 10.

[0131] Through the control of the operating parameters, it is advantageously possible to precisely control the characteristics of this second layer. Furthermore, good homogeneity of the second layer results from the gradual nature of the change in polarity of the medium.

[0132] At the same time there also form, but in much smaller proportions, copolymer micelles 14 free in the bath 11.

[0133] At the end of the self-assembly step c), as indicated at 32 in FIG. 1, a final rinsing step d) is carried out. This last step aims to eliminate the copolymer vesicles or micelles 14, as well as any aggregates, in solution, by a gradual replacement of the solvent of the bath 11 with water. Thus, as indicated at 13 in FIG. 1, water is added to the reservoir 12, at the same time as aspiration of the liquid contained therein is carried out, as indicated at 15 in FIG. 1.

[0134] At the end of this last step, an ultra-fine dual-layer membrane 16 is obtained on the solid support 10, with a thickness of less than 50 nm, and with controlled characteristics, provided with free hydrophilic functions on the surface.

[0135] The organic solvent removed from the reservoir 12 can be recycled with a view to subsequent reuse thereof.

[0136] The steps described above can be reiterated as many times as required, so as to form, one after another, successive layers of copolymer on the solid support, by successive variations in polarity of the medium, each dual layer formed being protected before forming the following dual layer.

[0137] The method according to the invention can be implemented in a similar manner for forming asymmetric dual-layer membranes, that is to say in which the two layers are formed differently from one another.

[0138] Thus, at the end of step al) in which the amphiphilic block copolymer 20 is attached to the solid support 10, the bath 11 in which this solid support is immersed may be replaced, in an intermediate step b), by a bath containing a different amphiphilic block copolymer, in solution in an organic solvent in which it has a high degree of solubility. This organic solvent may be identical or different to the one used in the first bath 11.

[0139] The following steps of the method according to the invention can then be implemented in the same way as described previously, to obtain an asymmetric dual-layer membrane, with perfectly controlled characteristics, in particular in terms of thickness of each of the layers and orientation of the blocks present at the surface thereof.

EXAMPLES

Equipment and Methods

[0140] The silicon plates come from the company Silicon Inc. Silica quartz crystal plates (14 nm in diameter) with a resonant frequency of 5 MHz are used for the QCM experiments.

[0141] The products (3-aminopropyl)triethoxysilane (APTES, 99%), anhydrous toluene (99.9%), N,N-dimethylformamide (DMF, 99.8%), tetrahydrofuran (THF, 98.9%), dioxane (99.8%), 4-nitrobenzaldehyde (98%) and dodecane (99%)) come from Sigma-Aldrich.

[0142] The block copolymers PS(42 kg/mol)-b-PAA(4.5 kg/mol) and PS(42 kg/mol)-b-POE(11.5 kg/mol) come from Polymer Source Inc. Each of them has a polydispersity index of less than 1.1.

[0143] The buffered aqueous solutions: 0.1M KCl/HCl (pH 1-2), acetate buffer at 0.1M (pH 3.5-5.5), phosphate buffer at 0.1M (pH 6-7.5), sodium carbonate buffer at 0.1M (pH 9-10), sodium phosphate 0.1M (pH 11), 0.1M (KCl/NaOH (pH 12-13) were used for dosing with two liquids via wetting.

[0144] Two Bioseb programmable syringe drivers, PTFE filters with pore sizes 20 nm, 0.1 m and 0.2 m coming from GE Healthcare Life Sciences and Nalgene were used. Deionised water was used for preparing the solutions.

[0145] Determination of the Grafting Density of the Amine Functions on the Surface of the Silica Plate

[0146] The plates functionalised by APTES are immersed for hours at 50 C. in a solution of absolute ethanol containing 0.08% vol. acetic acid and 0.05% by mass 4-nitrobenzaldehyde. After rinsing with ethanol in order to eliminate the excess 4-nitrobenzaldehyde, the plates were immersed in an aqueous solution of acetic acid at 0.15% for 1 hour. The concentration of 4-nitrobenzaldehyde is determined by UV-visible spectroscopy at 268 nm. This then makes it possible to determine the surface density of amine groups.

[0147] Ellipsometry Ellipsometry measurements are carried out at between 300 and 800 nm for three different angles (65, 70, 75, with a UVISEL (Horiba Scientific) ellipsometer. To establish the model, the values n=3.86, k=0.2 for the silica and n=1.46, k=0 for an organic film, are used.

[0148] TensiometryDetermination of Contact Angle

[0149] The wetting measurements are carried out in air using a TRACKER tensiometer (Teclis Scientific). A drop of water (with a volume of 2 l) is deposited by means of a syringe on the surface covered with a thin film. The detection of the contact angle is carried out continuously by means of a CCD camera connected to the control and analysis software. This measurement is determined by modelling the form of the drop using the Laplace equation: P=2/R. Monitoring of the evaporation of the drop of water over time makes it possible to determine the natural dewetting angle of the surface. The advancement angle (maximum), the withdrawal angle (minimum) and the hysteresis are then to be determined.

[0150] Atomic Force Microscopy (AFM)

[0151] The measurements are carried out in contact mode intermittently, in air and at ambient temperature, on ICON instrumentation (Bruker) equipped with a J-type scanner with a maximum analysis surface area of 100100 m.sup.2 and a limit height of 13 m. The images are analysed with WsxM software.

[0152] Quartz Crystal Microbalance with Dissipation (QCM-D-Q-Sense Biolin Scientific)

[0153] The kinetic monitoring of the in situ formation of a dual layer of block copolymers is carried out in a liquid cell of a quartz microbalance. QCM supports (Biolin Scientific) covered with a layer of silica previously functionalised with a monolayer of APTES are used.

[0154] Dynamic Diffusion of Light

[0155] The size and polydispersity of the suspensions of silica nanoparticles are determined before/after self-assembly of a dual layer of copolymer on the surface of the nanoparticles by dynamic diffusion of light at 90, by means of an ALV system equipped with an ALV-5000/E correlator.

Example 1Polystyrene-Block-Polyacrylic Acid Diblock Copolymer

[0156] The polystyrene-block-polyacrylic acid diblock copolymer, designated PS-b-PAA, of formula:

##STR00001##

comprises a hydrophobic polystyrene block with a number mean molar mass Mn=42 kg/mol greater than its intergrowth critical mass (Mc=32 kg/mol), and a hydrophilic polyacrylic acid block with a number mean molar mass Mn=4.5 kg/mol.

[0157] The polystyrene block (PS) has a hydrophobicity characterised by an interface tension with the water .sub.PS/water=32 mN/m, and a glass transition temperature of 100 C. The hydrophilic polyacrylic acid block (PAA) offers the possibility of participating in various types of bond with the substrate (acid-base or electrostatic, chelation). In this example, the interaction by acid-base is more particularly studied.

[0158] 1.1) Preparation of the Substrate

[0159] The solid support used is a flat plate (12 cm.sup.2) of silicon having on the surface a fine layer of native silicon oxide (silica SiO.sub.2), a few nanometres thick. To allow the formation of non-covalent interactions between this plate and the hydrophilic block of type PAA, a functionalisation of the substrate is necessary.

[0160] The silica plate is functionalised in a way that is conventional in itself, by an aminosilane (3-aminopropyltriethoxysilane APTES), in order to form on its surface a thin film comprising primary amine functions NH.sub.2. To this end, the silica plate is irradiated with UV-ozone in order to obtain reactive hydroxyl groups (OH) on the surface. The plate is next immersed for 1 hour in a 2% solution by mass of 3-aminopropyltriethoxysilane (APTES) in anhydrous toluene. The substrate is then rinsed with anhydrous toluene and stoved for 1 hour at 95 C.

[0161] The presence of the surface amine functions is verified by measurements of contact angle at various pH levels. The surface density of amine functions is determined by spectroscopic analysis with 4-nitrobenzaldehyde in accordance with a method described in the literature (Ho Moon et al. Langmuir, 1996, 12, 4621-4624). A surface density of 31.4 .sup.2/molecule is obtained. Analysis of the surface amine functions by measurement of contact angle at various pH levels reveals that the pKa of the amine functions is 6.5.

[0162] 1.2) Formation of a Copolymer Monolayer on the Support

[0163] The absorption on the solid support is effected in solution in a mixture of dimethylformamide DMF and tetrahydrofuran THF. This non-polar mixture is non-selective for the copolymer, both the hydrophilic block and the hydrophobic block having good solubility therein.

[0164] The polystyrene-block-polyacrylic acid copolymer having a PS block of 42000 g/mol (DP=404) and a PAA block of 4500 g/mol (DP=63) (PS.sub.403-b-PAA.sub.63) is dissolved at 1 g/l in a DMF/THF mixture (80/20 (v/v). The aminated silica plate is immersed for 2 hours in the copolymer solution previously filtered over a 0.1 m membrane.

[0165] The substrate is next rinsed with a DMF/THF mixture (80/20) (v/v) and dried for 2 days under a hood.

[0166] A monolayer of PS-b-PAA is formed, securely anchored to the surface of the solid support. This monolayer is characterised by measurement of contact angle, ellipsometry and AFM. The adsorption method is also monitored by means of a quartz crystal microbalance (QCM-D), which makes it possible to determine the quantity of copolymer adsorbed in the monolayer. It is determined that the layer of PS-b-PAA adsorbed on the solid support has a thickness of 5.8 nm, a contact angle .sub.A=91 and a hysteresis value =12.

[0167] The results of the analyses carried out are shown in FIG. 2. More particularly, for the QCM-D analysis (FIG. 2a), the appearance of an adsorption plateau as from a copolymer concentration of approximately 1010.sup.6 mol/1 (0.1 g/l) is noted, with a grafting density sat equal to approximately 10 mg.Math.m.sup.2. By analysis by AFM (FIG. 2b)) the appearance of islets resulting from the reorganisation of the chains when passing the good solvent/air interface is clearly observed. Analysis of the distribution of the heights of the copolymer islets on the surface (FIG. 2c)) for its part shows a thickness of the monolayer of approximately 5 nm, in agreement with the ellipsometry measurements.

[0168] The results of the analyses carried out show that the copolymer monolayer is homogeneous and has a thickness of around 5 nm. The formation of islets observed in AFM corresponds to a dewetting phenomenon occurring on the surface of the film when the latter passes through the water-air interface. From the adsorption isotherm, it is possible to calculate a grafting density of 0.15 copolymer chains/nm.sup.2, which is in good agreement with a conformation regime of the brush type obtained since the interchain separation distance is less than the size of the copolymer chain itself.

[0169] 1.3) Formation of a Symmetrical Dual Layer by Switching of Solvent

[0170] At the end of the step of immersion of the aminated silica plate for 2 hours in the previously filtered copolymer solution, as indicated above, water is added to the copolymer solution, which has an initial volume of 2 ml, in order to trigger self-assembly. This addition is carried out so as to obtain, above the solid support, a solvent height of between 2 and 3 nm. More precisely, the water is added to the copolymer solution at a rate of 0.3 ml/min using a syringe driver.

[0171] After 15 minutes, a proportion by volume of water in the bath of 49% has been obtained; while maintaining the injection of water, the solution is then pumped by means of another syringe driver, at a rate of 0.3 ml/min.

[0172] The simultaneous steps of injecting water and pumping the solution make it possible to eliminate the micelles/vesicles of self-assembled copolymers in solution while completely exchanging the initial organic solution for water.

[0173] After 2 hours of simultaneous injection and aspiration, the entire organic solution has been exchanged for pure water. The support is removed and put to dry under a hood for 1 day. A symmetrical dual-layer membrane has formed on its surface.

[0174] The dual layer thus self-assembled is characterised by contact angle measurement and ellipsometry. Its thickness measured by ellipsometry is 11 nm, that is to say approximately twice the thickness of its first layer (5.8 nm). The contact angle .sub.A measured in air at pH=7 is 91 with a hysteresis =31.

[0175] Dosing with two liquids is carried out in order to demonstrate the presence of the PAA blocks at the tops and to reveal the hydrophobic effect of the PS block. It makes it possible to define a pKa of 5.53 for the carboxylic acid group on the surface.

[0176] Furthermore, during the implementation of these steps, QCM-D analyses of the solid support are carried out, at regular time intervals. The dual layer finally obtained is further analysed by AFM. The results obtained are shown in FIG. 3. More particularly, FIG. 3a) shows the change in the quantity of adsorbed copolymer as a function of time. FIG. 3b) shows the image, obtained by AFM, of the self-assembled dual layer on the solid support.

[0177] As can be seen in this figure, in the first step of the method, a monolayer forms on the aminated surface of the substrate, with a density of approximately 10 mg.Math.m.sup.2 (which is in agreement with the adsorption isotherm in FIG. 2a)). In the second step, in which the solvent mixture is gradually replaced with water, a second monolayer forms on the surface, with a density of 10 mg.Math.m.sup.2. The dual layer thus formed has a final density of approximately 20 mg.Math.m.sup.2, that is to say twice the density of a monolayer. As can be seen in FIG. 3b), it has a smooth surface morphology, representative of the surface covered with PAA chains, more hydrophilic than those of PS. The total thickness of the dual layer is 10 nm.

Example 2Polystyrene-Block-Polyethylene Oxide Diblock Copolymer

[0178] The polystyrene-block-polyethylene oxide diblock copolymer, designated PS-b-POE, of formula:

##STR00002##

offers the possibility of forming hydrogen bonds with the substrate.

[0179] The copolymer used consists of a hydrophobic polystyrene block with a number mean molecular mass Mn=42 kg/mol and a hydrophilic polyethylene oxide block with a number mean molecular mass Mn=11.5 kg/mol.

[0180] 2.1) Preparation of the Substrate

[0181] The solid support used is a flat silicon plate (12 cm.sup.2) having on the surface a fine layer of native silicon oxide (silica SiO.sub.2), a few nanometres thick. To allow the formation of non-covalent interactions (hydrogen bonds) between this plate and the hydrophilic block of type POE, an ultraviolet-ozone treatment is carried out to introduce hydroxyl groups (OH) on the surface of the plate.

[0182] 2.2) Formation of a Copolymer Monolayer on the Support

[0183] The solvent used is toluene. This non-polar solvent is non-selective for the copolymer, both the hydrophilic block and the hydrophobic block having good solubility therein.

[0184] The polystyrene-block-polyethylene oxide copolymer having a PS block of 42000 g/mol (DP=404) and a POE block of 11500 g/mol (DP=261) (PS.sub.403-b-POE.sub.261) is dissolved at 1 g/l in toluene.

[0185] The oxidised silicon plate (SiOH) is immersed for 2 hours in the copolymer solution previously filtered on a 0.1 m membrane. The support is next rinsed with toluene and dried for 2 days under a hood.

[0186] A monolayer of PS-b-POE has formed, firmly anchored to the surface of the solid support. This monolayer is characterised by contact angle measurement, ellipsometry and AFM. The thickness of the monolayer formed, determined by ellipsometry, is 4.49 nm. This value is in agreement with the size of the copolymer in the toluene. It is relatively low, probably since the copolymer adopts a conformation of the mushroom type, because of the molar mass of the POE block, which is relatively high. Under these conditions, the PS block spreads more.

[0187] The measured contact angle is .sub.A=46.7 with a hysteresis =13.7.

[0188] The AFM images obtained, at various magnifications, are shown in FIG. 4. They confirm the adsorption of the POE-PS copolymers, from the toluene solution, on the silica surface, through hydrogen bonds formed between the POE block and the surface silanol groups. Because of the use of a POE block with a relatively high molar mass, the grafting density obtained is relatively low, which is illustrated by the presence of islets of PS spaced apart from each other. The use of POE with a lower molar mass makes it possible to increase the grafting density of the monolayer. Thus the grafting density can easily be adjusted by selecting a copolymer the hydrophilic block of which has a suitable molar mass.

[0189] 2.3) Formation of a Symmetrical Dual Layer by Switching Solvent

[0190] At the end of the step of immersing the oxidised silica plate for 2 hours in the copolymer solution as indicated above, self-assembly is triggered.

[0191] To this end, the copolymer solution is put in the presence of saturated water vapour generated by a hot-water reservoir (at approximately 50 C.) placed in the vicinity of the system, the whole under a hermetic bell so as to saturate the atmosphere above the solution with vapour.

[0192] The system is next rinsed by the injection of water while aspirating the non-miscible toluene. After 2 hours, the support is removed and set to dry under a hood for 2 days.

[0193] A self-assembled asymmetric dual layer is obtained on the solid support.

Example 3Formation of PS-b-PAA and PS-b-POE Asymmetric Dual Layer

[0194] A PS-b-PAA monolayer is formed as in example 1.2) above. The self-assembly of this monolayer is next carried out with a second block copolymer (PS-b-POE), comprising a hydrophilic block that is different but a hydrophobic block that is identical to that of the monolayer.

[0195] To this end, at the end of this step of immersion of the aminated silica plate for 2 hours in the copolymer solution, as indicated above, the DMF/THF mixture (80/20) is replaced by a polystyrene-block-polyethylene oxide copolymer solution having a PS block of 42000 g/mol (DP=404) and a POE block of 11500 g/mol (DP=261) (PS.sub.403-b-POE.sub.261) at 1 g/l in toluene, the solvent in which the copolymer is best solubilised. Prior to this, the solid support was rinsed with the organic solvent of the first layer (DMF/THF), in order to discharge the non-adsorbed block copolymers in solution.

[0196] The self-assembly of the dual layer is next triggered by putting the copolymer solution in the presence of saturated water vapour generated by a hot-water reservoir (at approximately 50 C.) placed in the vicinity of the system, the whole under a hermetic bell for 4 hours.

[0197] The system is next rinsed by injecting water while aspirating the non-miscible toluene, at injection and aspiration rates each of 0.3 ml/min. After 2 hours, the support is removed and set to dry under a hood for 2 days.

[0198] The asymmetric dual layer thus self-assembled is characterised by contact angle measurement, ellipsometry and AFM. The macroscopic thickness thereof measured by ellipsometry is 17 nm. The wetting angle values at a relatively low advance .sub.A=82 and a hysteresis =22 are consistent with the formation of a dual layer with POE on the surface.

[0199] As shown by the image obtained by AFM, shown in FIG. 5, the dual layer has a mushroom-type structure. This is due to the presence of the POE blocks on the surface of the membrane, which have a high molar mass, and which will collapse when passing through the water/air interface.

[0200] The structure, with a roughness of 2.43 nm, has holes with a maximum depth of 15.4 nm and a mean thickness of the surface objects of 8.36 nm (as shown by the height distribution graph shown in FIG. 5b)). These data demonstrate the formation of a dual layer with a mean thickness for the PS-b-POE layer of 8.36 nm and a total thickness of approximately 16 nm, in agreement with ellipsometry measurements.

Example 4Self-Assembly on the Surface of Nanoparticles

[0201] The previous three examples, carried out on microscopic flat surfaces of oxidised silica (SiOH) and aminated silica (NH.sub.2) are transposed on silica nanoparticles (diameter 200 nm), both in oxidised form and in aminated form.

[0202] At the end of the addition of water, in liquid form or in vapour form depending on the organic solvents used, the particles are centrifuged, the supernatant is eliminated and water is added to wash the particles. This procedure is repeated at least once more in order to eliminate the entire free polymer in solution as well as the residual traces of solvent.

[0203] The sizes of the silica nanoparticles are measured by dynamic diffusion of light before and after self-assembly of the copolymer dual layer. The difference in size makes it possible to measure the thickness of the membrane formed on the surface of the particles. This is typically between 15 and 30 nm.

Example 5Encapsulation of Gold Nanoparticles in a Dual-Layer Membrane Formed Based on Polystyrene-Block-Polyacrylic Acid Diblock Copolymer

[0204] The copolymer used in this example is a polystyrene-block-polyacrylic acid diblock copolymer, designated PS.sub.403-b-PAA.sub.63, having a PS block of 42000 g/mol (DP=404) and a PAA block of 4500 g/mol (DP=63). The solid support is a flat silicon plate functionalised as described in example 1.1).

[0205] A monolayer of PS.sub.403-b-PAA.sub.63 is generated on the solid support as described in example 1.2).

[0206] A solution of PS.sub.403-b-PAA.sub.63 at 1 g/l and hydrophobic gold nanoparticles (NP) (diameter3-4 nm) at 110.sup.6 NP/l in a dimethylformamide/tetrahydrofuran (DMF/THF) mixture (80/20) (v/v) is also prepared. This solution is added to the receptacle containing the PS.sub.403-b-PAA.sub.63 monolayer. Water is next added to this copolymer/nanoparticle hybrid solution, which has an initial volume of 3 ml, in order to trigger self-assembly as described in example 1.3), so as to produce a symmetrical dual-layer membrane. This addition is carried out at a rate of 0.3 ml/min using a syringe driver, so as to obtain, above the solid support, a solvent height of between 3 and 4 mm.

[0207] After 15 minutes, a proportion of water by volume in the bath of 49% is obtained; while maintaining the injection of water, the solution is then pumped by means of another syringe driver, at a rate of 0.3 ml/min.

[0208] During these operations, the gold nanoparticles are encapsulated inside the dual-layer membrane generated on the support, as well as in the micelles formed in volume. The simultaneous steps of injecting water and pumping the solution eliminate these hydride micelles of self-assembled copolymers in solution, while completely exchanging the initial organic solution for water. After 2 hours of simultaneous injection and aspiration, the entire organic solution has been exchanged for pure water. The support is removed and set to dry under a hood for one day.

[0209] At the end of this method, as shown in FIG. 6, on the surface of the solid support 10, a symmetrical dual-layer membrane is obtained, formed from the amphiphilic block copolymer 20 and containing gold nanoparticles 23 encapsulated in the hydrophobic reservoir formed by the hydrophobic polystyrene blocks 22.

[0210] The dual layer thus self-assembled is characterised by contact angle measurement and ellipsometry as described in example 1. Its thickness measured by ellipsometry is 13 nm, that is to say a little more than twice the thickness of its first layer (5.8 nm). The contact angle .sub.A measured in air at pH=7 is 89 with a hysteresis =35.

[0211] The solid support covered with this dual-layer membrane containing gold nanoparticles is then characterised by conventional UV-visible transmission spectroscopy. As shown in FIG. 7, the hydrophobic gold nanoparticles have, in the hydrophobic polystyrene reservoir, a characteristic plasmon signature, at approximately 525 nm, suggesting a successful encapsulation (continuous black curve). The broken black curve for its part represents the gold nanoparticles in solution (in the THF/DMF mixture) with their characteristic plasmon peak at around 520 nm. The difference in absorption between these two curves results from a different detected volume in solution (50 mm bowl) and in the dual-layer membrane (approximately 35 nm). The slight displacement in wavelength results from the change in dielectric environment of the nanoparticles in passing from the solution (THF/DMF) to the dual-layer membrane.