Patent Application: US-201214233030-A

Abstract:
a method for producing a porous polymer structure involves forming a polymer ; subsequently contacting the polymer with a nonsolvent and inducing the formation of an emulsion in which the nonsolvent is present as the dispersed phase and the polymer as the continuous phase ; and removing at least some of the nonsolvent so as to leave pores within the polymer , wherein the polymer is formed by exciting one or more molecules in an exciting medium , in particular by pulsed plasma deposition . emulsion formation in step may be induced by or in the presence of an emulsion stabilising agent . also provided is a porous polymer structure produced using the method , and a polymer which is impregnated with an emulsion stabilising agent , for use in the emulsion formation step of the method .

Description:
the fig1 scheme the scheme shown in fig1 illustrates a method in accordance with the invention , in which : step 1 — a poly ( vinylbenzyl chloride ) film 10 is deposited onto a substrate 11 using a pulsed plasma deposition process ; step 2 — the polymer film is impregnated with an amphiphilic surfactant ( in this case cresyl violet perchlorate ) by immersing the coated substrate 11 in an aqueous solution of the surfactant ; step 3 — the impregnated polymer layer is rinsed in water at an elevated temperature , followed by drying , in order to generate a network of interconnected pores 12 throughout the polymer ; and step 4 — the pores are surface functionalised using , in this case , an atrp process and an epoxide reagent . in this example , a porous poly ( vinylbenzyl chloride ) structure was prepared in accordance with the invention . plasma depositions were performed inside a cylindrical glass reactor ( 5 . 5 cm diameter , 475 cm 3 volume ) located within a faraday cage . the system was evacuated using a 30 l min − 1 mechanical rotary pump via a liquid nitrogen cold trap ( base pressure less than 3 × 10 − 3 mbar and leak rate better than 6 × 10 − 9 molecules per second [ 39 ]). a copper coil wound around the reactor ( 4 mm diameter , 10 turns , located 10 cm away from the gas inlet ) was connected to a 13 . 56 mhz radio frequency ( rf ) power supply via an l - c matching network . the rf power supply was triggered using a signal generator . all apparatus was thoroughly scrubbed with detergent and hot water , rinsed with propan - 2 - ol , and oven dried . substrate preparation comprised successive sonication of glass microscope slides ( vwr international llc ) or silicon wafers ( memc electronic materials inc ) in propan - 2 - ol and cyclohexane for 15 minutes each prior to insertion into the centre of the plasma reactor . further cleaning entailed running a 50 w continuous wave air plasma at 0 . 2 mbar for 30 minutes . vinylbenzyl chloride precursor (+ 97 %, aldrich ) was loaded into a sealable glass tube , degassed via several freeze - pump - thaw cycles , and attached to the plasma deposition chamber . monomer vapour was then allowed to purge through the apparatus at a pressure of 0 . 2 mbar for 3 minutes prior to electrical discharge ignition . optimum pulsed plasma deposition duty cycle parameters were 100 μs on - period and 4 ms off - period in conjuction with 30 w peak power [ 31 ]. following plasma extinction , precursor vapour was allowed to continue to pass through the system for a further 3 minutes , followed by evacuation to base pressure . substrates bearing 3 μm thick pulsed plasma deposited poly ( vinylbenzyl chloride ) layers were immersed into a 0 . 15 mg l − 1 aqueous solution of cresyl violet perchlorate ( analytical grade , aldrich ) for 16 hours . following removal from solution , the samples were thoroughly rinsed with high purity water ( bs 3978 grade 1 ), and soaked in fresh high purity water for an additional 16 hours at room temperature . in order to induce pore formation , the samples were then placed inside a sealed jar containing high purity water and stored at 60 ° c . for 1 hour . finally , the films were dried under ambient conditions for 16 hours prior to analysis . fig2 shows schematically a further polymer - functionalising step which was carried out on the macroporous polymer structure as follows . the process used for the functionalising step was atrp ( atom transfer radical polymerisation ). porous poly ( vinylbenzyl chloride )- functionalised substrates were placed inside a sealable glass tube containing 5 mmol copper ( i ) bromide (+ 98 %, aldrich ), 1 mmol copper ( ii ) bromide (+ 99 %, aldrich ), 12 mmol 2 , 2 ′- bipyridyl (+ 99 . 9 %, aldrich ), 0 . 05 mol glycidyl methacrylate (+ 97 %, aldrich ), and 4 ml propan - 2 - ol ( reagent grade , fisher ). the mixture was thoroughly degassed using freeze - pump - thaw cycles and then allowed to undergo polymerisation at room temperature for 4 hours . cleaning and removal of any physisorbed atrp polymer was accomplished by successive rinsing with propan - 2 - ol and tetrahydrofuran . fluorescent tagging of the surface grafted poly ( glycidyl methacrylate ) epoxide centres was achieved by brief submersion into a 1 mg dm − 3 aqueous solution of alexafluor 350 cadaverine dye ( analytical grade , invitrogen ltd ), followed by extensive rinsing with high purity water . thus , as seen in fig2 , the polymer layer 20 on the substrate 21 is firstly grafted with the glycidyl methacrylate 22 , following which nucleophilic ring opening of the epoxide centres by the dye 23 results in a labelled polymer layer 24 . film thicknesses following pulsed plasma deposition were measured using a spectrophotometer ( nkd - 6000 , aquila instruments ltd ). transmittance - reflectance curves ( 350 - 1000 nm wavelength range ) were acquired for each sample and fitted to a cauchy material model using a modified levenberg - marquardt algorithm [ 40 ]. surface elemental compositions were obtained by x - ray photoelectron spectroscopy ( xps ) using a vg escalab ii electron spectrometer equipped with a non - monochromated mg kα x - ray source ( 1253 . 6 ev ) and a concentric hemispherical analyser . photoemitted electrons were collected at a take - off angle of 20 ° from the substrate normal , with electron detection in the constant analyser energy mode ( cae , pass energy = 20 ev ). experimentally determined instrument sensitivity factors were taken as c ( 1s ): n ( 1s ): o ( 1s ): cl ( 2p ) equals 1 . 00 : 0 . 63 : 0 . 39 : 0 . 35 . infrared spectra were acquired using a ftir spectrometer ( perkin - elmer spectrum one ) operating with a liquid nitrogen cooled mct detector set at 4 cm − 1 resolution across the 700 - 4000 cm − 1 range . the instrument was fitted with a variable angle reflection - absorption accessory ( specac ) set to an angle of 66 ° for silicon wafer substrates and adjusted for p - polarisation . fluorescence microscopy was performed using an olympus ix - 70 system ( deltavision rt , applied precision inc , wa ). images were collected using excitation wavelengths of 640 nm and 360 nm corresponding to the absorption maxima of cresyl violet perchlorate and the alexafluor 350 cadaverine dye respectively . surface micrographs were obtained with a scanning electron microscope ( cambridge stereoscan 240 ). prepared specimens were placed onto carbon discs and then mounted onto aluminium holders , followed by deposition of 15 nm gold coating ( polaron sem coating unit ). for cross - sectional images , samples were frozen and snapped under liquid nitrogen prior to mounting . afm images were acquired in tapping mode at 20 ° c . in ambient air ( digital instruments nanoscope iii , santa barbara , calif .). the tapping mode tip had a spring constant of 42 - 83 nm − 1 ( nanoprobe inc ). sessile drop contact angle measurements were made at 20 ° c . using a video capture apparatus ( vca 2500 xe , ast products inc ) and 2 μl high purity water droplets ( bs 3978 grade 1 ). xps analysis of pulsed plasma deposited poly ( vinylbenzyl chloride ) yielded elemental compositions corresponding to the expected theoretical values based on the vinylbenzyl chloride precursor , thereby indicating good structural retention of the benzyl chloride functionality [ 31 ]— see table 1 below . in addition , the absence of a si ( 2p ) xps signal confirmed pinhole - free coverage of the underlying silicon wafer substrate . further evidence for the structural integrity of the pulsed plasma deposited poly ( vinylbenzyl chloride ) films was obtained by infrared spectroscopy , where the main fingerprint features matched those associated with the monomer . the infrared spectra are shown in fig3 , in which trace ( a ) is the vinylbenzyl chloride monomer ; ( b ) is the pulsed plasma deposited poly ( vinylbenzyl chloride ); ( c ) is the pulsed plasma deposited poly ( vinylbenzyl chloride ) following immersion in cresyl violet perchlorate solution ; ( d ) is the dye - impregnated polymer following 16 hours &# 39 ; water rinsing at 22 ° c . and 16 hours &# 39 ; drying in air at 22 ° c . ; ( e ) is the product ( d ) following its immersion in water at 60 ° c . for 1 hour and then drying for 16 hours in air at 22 ° c . ; ( f ) is the poly ( glycidyl methacrylate ) atrp grafted onto the product ( e ); and ( g ) is the glycidyl methacrylate monomer . both trace ( b ) for the plasma deposited polymer and trace ( a ) for the monomer include the halide functionality at 1263 cm − 1 ( ch 2 wag mode for ch 2 — cl ) and parasubstituted benzene ring stretches at 1495 cm − 1 and 1603 cm − 1 [ 41 ]. in addition , the disappearance of the vinyl double bond stretch at 1629 cm − 1 is consistent with polymerisation . a linear film deposition rate of 191 ± 17 nm min − 1 and water contact angle values of 80 ± 1 ° ( not hydrophilic ) were measured . optical micrographs and fluorescence images ( gathered at the excitation wavelength for cresyl violet perchlorate ) were both featureless , thereby confirming that the deposited films were smooth and homogenous . fig4 shows the fluorescence and corresponding optical micrographs (× 10 magnification ) of the poly ( vinylbenzyl chloride ) film ( a ) as deposited ; ( b ) following immersion in cresyl violet perchlorate solution ; and ( c ) following immersion in cresyl violet perchlorate solution , rinsing in water at 22 ° c . for 16 hours , soaking in water at 60 ° c . for 60 minutes , and then drying in air at 22 ° c . for 16 hours . fluorescence microscopy showed that immersion of the pulsed plasma deposited poly ( vinylbenzyl chloride ) films in cresyl violet perchlorate solution for 16 hours resulted in uptake of the fluorophore , as seen in fig4 . subsurface penetration of the cresyl violet perchlorate was evident by the greater number of crystals detected by fluorescence microscopy compared to those visible at the surface by optical microscopy ( again , see fig4 ). furthermore , xps elemental analysis confirmed the presence of cresyl violet perchlorate on the surface of the pulsed plasma deposited layers via detection of n ( 1s ) and o ( 1s ) fluorophore signals , as seen in table 1 . infrared spectroscopy identified a broad absorbance centred at 1690 cm − 1 ( h — o — h bend attributed to the crystallisation of water associated with cresyl violet perchlorate ) [ 41 , 42 ], as seen in fig3 . this was found to be absent when n , n - dimethyl formamide was employed instead of water as the solvent for cresyl violet perchlorate under otherwise identical conditions ( n , n - dimethyl formamide is an alternative polar solvent which dissolves cresyl violet perchlorate [ 43 ]). retention of the benzyl chloride infrared absorbances confirmed that no chemical changes to the polymer bulk had taken place during contact with the cresyl violet perchlorate solution ( fig3 ). in addition to the aforementioned macroscale examination by fluorescence and optical microscopy , afm was employed to monitor the microscale structure . the resultant 20 μm × 20 μm afm micrographs are shown in fig5 . tapping mode height images confirmed that the pulsed plasma deposited poly ( vinylbenzyl chloride ) surfaces were featureless ( a ), and only a slight roughening was visible following 16 hours &# 39 ; immersion in high purity water and then drying in air at 22 ° c . for 16 hours ( b ). in contrast , immersion in aqueous cresyl violet perchlorate solution for 16 hours and then drying in air at 22 ° c . for 16 hours gave rise to crater formation around crystals on the film surface ( c ). subsequent rinsing of these samples in high purity water at room temperature for 16 hours , followed by drying in air at 22 ° c . for 16 hours , removed the crystals to yield additional crater features ( d ). partial removal of cresyl violet perchlorate from the surface during rinsing is supported by xps analysis , which indicated a corresponding drop in surface oxygen and nitrogen content associated with the fluorophore , as seen in table 1 . interactions between cresyl violet perchlorate and the pulsed plasma deposited poly ( vinylbenzyl chloride ) films were further investigated using 4 - methylbenzyl chloride as an analogue to represent the pendant benzyl chloride functionality contained in the polymer layers . infrared spectra taken for 1 g dm − 3 solutions of cresyl violet perchlorate in 4 - methylbenzyl chloride showed no perturbation in the position or intensity of the fingerprint region infrared absorbances for 4 - methylbenzyl chloride , thereby providing further confirmation that no chemical reaction is to be expected to occur between the pulsed plasma deposited poly ( vinylbenzyl chloride ) layers and cresyl violet perchlorate . the infrared spectra for this part of the experiment are shown in fig6 , in which trace ( a ) is 4 - methylbenzyl chloride ; ( b ) is the 0 . 1 mg dm − 3 solution of cresyl violet perchlorate in 4 - methylbenzyl chloride ; ( c ) is the solvent - subtracted spectrum of cresyl violet perchlorate dissolved in 4 - methylbenzyl chloride ; ( d ) is the solvent - subtracted spectrum of cresyl violet perchlorate dissolved in water ; and ( e ) is the cresyl violet perchlorate bulk crystalline material . table 2 below summarises the full - width - at - half - maximum ( fwhm ) peak widths corresponding to fig6 . subtraction of the 4 - methylbenzyl chloride infrared spectrum from that of the solution yielded the characteristic absorbances of cresyl violet perchlorate . these absorbances were comparable in width to those measured for cresyl violet perchlorate dissolved in water , and notably sharper than those observed for the bulk crystalline material . this is indicative of free rotation in both liquids , ie cresyl violet perchlorate can be solvated by both water and 4 - methylbenzyl chloride ( and therefore by polyvinylbenzyl chloride ). in order to create macropores , the samples which had been immersed in aqueous cresyl violet perchlorate solution , and rinsed in water , were stored in high purity water for 1 hour at 60 ° c . during this period , the polymer layer appearance changed from translucent ( prior to heating ) to opaque , and remained so upon subsequent drying in air . fluorescence and optical micrographs revealed an interconnected polyhipe structure with pore diameters of 1 - 10 μm ( which is comparable to the 3d pore geometry of conventional polyhipe structures ), as seen in fig4 . these macropores were also clearly visible by high resolution sem : see fig7 . the four sem images in fig7 are of the pulsed plasma deposited poly ( vinylbenzyl chloride ) following 16 hour immersion in aqueous cresyl violet perchlorate solution and then : ( a ) subsequent immersion in water at 22 ° c . for 1 hour and drying in air at 22 ° c . for 16 hours ; and ( b )-( d ) subsequent immersion in water at 60 ° c . for 1 hour and drying in air at 22 ° c . for 16 hours , where ( d ) corresponds to the cross - section . the pore diameters ranged from 1 to 10 μm . the interconnecting pore hole size range was 201 ± 65 nm in diameter . the pore wall thickness range was 172 ± 80 nm . the smooth and largely spherical pore morphology is consistent with solvent templating [ 44 , 45 , 46 ]. cross - sectional sem micrographs confirm that porosity extends throughout the polymer films , which are distended from an initial thickness of 3 μm to 10 μm . these measurements effectively eliminate partial dissolution of plasmachemical polymer layers as being an alternative explanation for the creation of pores [ 37 ]. pulsed plasma deposited poly ( vinylbenzyl chloride ) layers have previously been used for the initiation of atrp to create polymer brushes [ 31 , 33 ]. the infrared spectra of the fabricated porous poly ( vinylbenzyl chloride ) films indicated retention of the atrp initiating benzyl chloride functionality ( fig3 ). after atrp grafting of glycidyl methacrylate onto the macroporous films , infrared spectroscopy showed characteristic signature absorbances of poly ( glycidyl methacrylate ) [ 27 , 41 ] at 1726 cm − 1 ( c ═ o ester stretch , instead of 1714 cm − 1 for the monomer due to conjugation with the vinyl group ), 1152 cm − 1 ( c — o stretch ), 1254 cm − 1 ( epoxide ring breathing ), 906 cm − 1 ( antisymmetric epoxide ring deformation ), and 841 cm − 1 ( symmetrical epoxide ring deformation ): again , see fig3 . absence of the glycidyl methacrylate monomer vinyl absorbances at 1637 cm − 1 ( c ═ c stretch ) and 941 cm − 1 ( vinyl ch 2 wag ) provided additional evidence for atrp having taken place . subsequent fluorescent tagging of the poly ( glycidyl methacrylate ) brushes via nucleophilic ring opening of the epoxide centres was carried out using a dilute solution of alexafluor 350 cadaverine dye ( fig2 ). fluorescence microscopy confirmed reaction of the fluorophore with the poly ( glycidyl methacrylate ) brushes , as seen in fig8 . imaging at the excitation wavelengths of 640 nm and 360 nm for both cresyl violet perchlorate and alexafluor 350 cadaverine dye respectively confirmed the grafting of poly ( glycidyl methacrylate ) brushes directly onto the underlying porous structure . in fig8 , fluorescence micrographs ( a ) and ( b ) show the pulsed plasma deposited poly ( vinylbenzyl chloride ) film following immersion in aqueous cresyl violet perchlorate solution for 16 hours and rinsing in water at 60 ° c . for 1 hour ( red excitation at 640 nm for cresyl violet perchlorate ); whilst ( c ) and ( d ) show the resultant macroporous film following its exposure to atrp grafting conditions for glycidyl methacrylate for 4 hours and then immersion in alexafluor 350 cadaverine dye ( excitation wavelengths for cresyl violet perchlorate ( 640 nm — red ) and alexaflour 350 cadaverine dye ( 360 nm - blue )). a series of control experiments , using alternative reagents , was undertaken to further elucidate the mechanism of pore formation . these experiments employed identical conditions to those used in example 1 to generate macroporous structures in pulsed plasma deposited poly ( vinylbenzyl chloride ) films ( ie 16 hour immersion in cresyl violet perchlorate solution , 16 hour rinsing in nonsolvent ( water ) at 22 ° c ., immersion in nonsolvent at 60 ° c . for 1 hour , and air drying ). first of all , rinsing the polymer films with only deionised water ( in the absence of cresyl violet perchlorate ) produced no porosity ( featureless afm , fluorescence and optical micrographs ), thereby confirming that the surfactant plays , in this case , a critical role in pore formation . replacement of water with n , n - dimethyl formamide ( an alternative polar solvent ) throughout also resulted in the absence of porosity , which demonstrates the importance of the nonsolvent ( in this case water ) for templating . finally , the choice of sodium dodecyl sulphate as a different amphiphile for mediating the interaction between water and polymer ( 16 hour immersion in 0 . 5 % ( w / v ) aqueous sodium dodecyl sulphate solution at 22 ° c ., followed by rinsing in water , heating at 60 ° c . in water for one hour , and drying in air at 22 ° c . for 16 hours ) caused the appearance of the polymer film to change from translucent to opaque during heating . sem images taken after drying ( see fig9 ) revealed the formation of macroporous ( polyhipe ) structures , thereby confirming that amphiphilic surfactant action between water and pulsed plasma deposited poly ( vinylbenzyl chloride ) can underpin the formation of the macroporous structures . atrp grafted poly ( glycidyl methacrylate ) brushes tagged with alexafluor 350 cadaverine dye have previously been shown to exhibit solvent responsive behaviour [ 47 ]. owing to the hydrophilic nature of the fluorophore , these tagged brushes swell upon exposure to water , which in turn can be removed by exposure to hygroscopic organic solvents . afm topography measurements of the atrp grafted macroporous polymer film produced in example 1 showed complete coverage of pore features , thereby indicating that the swollen tagged poly ( glycidyl methacrylate ) brushes had filled the pores . in this example , the thickness ( length ) of the atrp - grafted poly ( glycidyl methacrylate ) brushes had been optimised so as to be comparable in dimension to the host pore sizes when extended ( swollen ). furthermore , the underlying porous poly ( vinylbenzyl chloride ) structure could be observed using fluorescence microscopy taken at the excitation wavelength for cresyl violet perchlorate ( 640 nm - red ), whilst images taken using the excitation wavelength of alexafluor 350 cadaverine dye ( 360 nm - blue ) over the same area showed very little contrast , indicating the presence of the tagged polymer brushes across the entire pore structure . the 50 μm × 50 μm tapping mode afm images ( z scale is 1500 nm ) and corresponding fluorescence micrographs are shown in fig1 . the images show the pulsed plasma deposited poly ( vinylbenzyl chloride ) ( a ) following immersion in aqueous cresyl violet perchlorate solution and then rinsing at 60 ° c . for 1 hour ; ( b ) following exposure of ( a ) to atrp grafting conditions for glycidyl methacrylate for 12 hours , brief immersion in alexafluor 350 cadaverine dye and then 16 hours &# 39 ; aqueous rinsing at 22 ° c . ; and ( c ) following immersion of ( b ) in tetrahydrofuran and drying . as verified by the fluorescence micrographs and the afm height images in fig1 , water removal ( accomplished by soaking the polymer layer in the hygroscopic solvent tetrahydrofuran ) resulted in the restoration of porosity . this behaviour was found to be reversible , and can therefore be used as the basis for pore actuation . in the present case , the favourable interaction of cresyl violet perchlorate with both water and poly ( vinylbenzyl chloride ) can be understood by consideration of its molecular structure , as seen in fig1 . the ionic component of the dye molecule confers hydrophilicity , whilst the extended aromatic structure facilitates interaction with the benzyl chloride moieties contained within the poly ( vinylbenzyl chloride ). control experiments using 4 - methylbenzyl chloride have confirmed this behaviour , as seen in fig6 . indeed , many similar organic dyes have previously been shown to disperse within aromatic polymer matrices via π - π interactions [ 51 , 52 ]. the utilisation of an alternative amphiphilic species ( sodium dodecyl sulphate , which is known to mediate interactions between vinylbenzyl chloride and water [ 53 , 54 ]) has also been shown to impart porosity in a poly ( vinylbenzyl chloride ) matrix . in contrast , the use of an organic solvent ( for example n , n - dimethyl formamide ) instead of water is less likely to lead to emulsion formation with aromatic polymers due to its higher miscibility with them [ 55 ]. indeed , poly ( vinylbenzyl chloride ) has been reported to dissolve in n , n - dimethyl formamide [ 56 ], which helps to account for why the pulsed plasma deposited poly ( vinylbenzyl chloride ) layers used in these experiments were not templated by n , n - dimethyl formamide solutions . in keeping with conventional bulk emulsion polymerisation methods , a finite amount of the surfactant is likely to be retained within the porous polymer structure [ 57 ]. this is due to the equilibrium dispersion of surfactant between the organic and aqueous phases . uv - vis measurements showed that cresyl violet perchlorate partially disperses from aqueous solutions into 4 - methyl benzyl chloride liquid , and vice versa following a 16 hour equilibration period . in the present study , the retention of a very small amount of the cresyl violet perchlorate fluorophore within the porous polymer films has allowed fluorescence microscopy to be used as an analytical tool , which offers the advantage of film inspection under ambient conditions ( in contrast to sem ) as well as the potential for examination of subsurface morphology . apart from the mediating effect of surfactants , the stability of conventional water - in - oil microemulsions can also be enhanced by increasing the viscosity of the organic phase [ 58 ]. in the case of a pulsed plasma deposited poly ( vinylbenzyl chloride ), although the polymer is not sufficiently flexible at room temperature to form emulsions , the plasmachemical layer can be considered to become a highly viscous organic phase at elevated temperatures . afm height images show shallow crater formation at the film surface following exposure to cresyl violet perchlorate solution under ambient conditions , which is indicative of a limited amount of film deformation occurring at the solid - liquid interface around water droplets in order to maximise interfacial contact , as seen in fig5 . however , this effect is enhanced at raised temperatures , with the greater polymer chain mobility allowing the molecules to stretch around water droplets to create an emulsion . this is akin to the thermoplastic behaviour of conventional poly ( vinylbenzyl chloride ), which becomes more flexible at elevated temperatures [ 59 , 60 ]. the presently proposed mechanism for pore generation can therefore be influenced by a combination of surfactant ( stabilising agent ) action and polymer flexibility . a key feature of the invention is that unlike many traditional approaches where polymerisation takes place post emulsion ( pore ) formation , the present method effectively decouples the polymerisation step completely from emulsion formation , which can give the processing advantages referred to above . this is important given that conventional emulsions used to fabricate polyhipe materials are highly complex formulations comprising solvents , surfactants , monomer ( s ), cross - linker , and polymerisation initiators , where the molecular structure and concentration of each of these components affects emulsion stability and the resulting pore dimensions and morphology [ 48 , 61 ]. in such cases , porosity is also influenced by further factors including the material of the container contacting the emulsion during polymerisation , temperature , and mixing speed [ 48 ]. overall this means that a delicate balance of process conditions is required to reproducibly fabricate conventional open cell macroporous polymers . by decoupling the polymerisation and pore formation steps , the present method can allow better control over the macromolecular architecture for a variety of surfactants ( including cresyl violet perchlorate , which is not ordinarily considered to behave as a surfactant due to its small size ). raising the temperature can be expected to affect the flexibility of the polymer layer during the pore formation step , which will lead to increased coalescence of water phase droplets to yield larger pore sizes ( analogous to decreasing the viscosity of the organic phase of a standard hipe mixture [ 59 , 60 , 65 ]). other variables for controlling pore size include pressure [ 66 ] and surfactant concentration [ 67 ]. furthermore , given that the flexibility of a plasma - deposited polymer layer can be controlled by varying the plasma deposition parameters , this can also provide a means for tailoring pore geometries . the invented method can , moreover , allow the pore architecture and the surface functionality to be controlled independently of one another . the practical advantages of the technique described in this example include that the plasmachemical deposition step is substrate - independent and solventless , whilst the spontaneous emulsion formation requires only the use of environmentally friendly aqueous solutions . a straightforward extension of this approach can be envisaged for the fabrication of a whole host of functionalised porous structures , given the wide range of plasmachemical deposited functional layers that are available . in addition , the porous structures generated by this method can be further functionalised by either plasmachemical or conventional wet techniques ( eg atrp ), which can broaden the scope for potential applications ( given the wide array of monomers and functionalities available - including bioactive hydrophilic polymers [ 62 , 63 ]). 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