3852
Langmuir 1999, 15, 3852-3858
Polymerization of Aminoethyl Elaidamide in Langmuir and Langmuir-Blodgett Films Studied by SFM V. De´rue,* S. Alexandre, and J. M. Valleton UMR 6522, CNRS/Universite´ de Rouen, Universite´ de Rouen, 76821 Mont-Saint-Aignan, France Received July 24, 1998. In Final Form: February 2, 1999 The polymerization of aminoethyl elaidamide in Langmuir and Langmuir-Blodgett films has been studied. In Langmuir films, changes induced by the polymerization process were investigated by pressure/ area isotherm measurements and after transfer of the irradiated film by scanning force microscopy and IR spectroscopy. The pressure/area isotherms showed a phase transition at 16 mN/m, vanishing when the irradiation time is increased. At low resolution, scanning force microscopy images revealed that the irradiation induced the formation of structured domains. The shapes of these domains and the area occupied by these domains are dependent on irradiation time. At intermediate resolution, these domains which correspond to the polymeric phase appeared to be constituted of fibrillar structures characteristic of a crystalline polymer. Besides these domains, the film has a similar structure to the monomer film. For the polymerization in LB films, the changes in the structure of the film were followed by scanning force microscopy and IR spectroscopy as a function of irradiation time. Few changes in surface topography were observed at the micrometer scale during the polymerization. However we observed an increase of tip/ sample interactions with irradiation time; moreover the irradiated film was found to be unsoluble. These results are indirect proofs of the polymerization.
Introduction Several membrane systems have been used in the separation of gas mixtures for industrial purposes. Nevertheless, the development of new membranes possessing a higher selectivity than currently available membranes is necessary. This high selectivity must be obtained while keeping high permeability properties. For the separation of CO2 from other gas, different membrane systems have been considered. The transport of CO2 through liquid membranes1 and ion-exchange membranes2 was studied. However in the case of these two membrane systems, the problem is the loss of the liquid phase in which the carrier is solubilized. To overcome the liquid loss, other types of membranes were used in which the carrier is covalently attached to the polymer film and in which no solvent is required.3 However, in this case, the permeation rate is limited due to the thickness of the membrane. One approach to combine a high permeation and a high selectivity is the elaboration of composite membranes. Langmuir-Blodgett (LB) technology4 allows the elaboration of composite membranes5,6 by deposition of a functionalized amphiphilic film on a porous membrane. The low thickness of the deposited film allows a high permeation rate through the composite membrane; in addition, its functionality leads to a highly selective transport. The major drawback is the low thermal and mechanical stabilities of LB films. The polymerization of such films is a possible way to overcome this drawback. Indeed it was shown that the polymerization could improve the stability without modifying the gas permeability.7 Polymeric LB films can be prepared with low molecular weight (1) Otto, N. C.; Quinn, J. A. Chem. Eng. Sci. 1971, 26, 949. (2) Langevin, D.; Pinoche, M.; Se´le´gny, E.; Me´tayer, M.; Roux, R. J. Membr. Sci. 1993, 82, 51. (3) Yoshikawa, M.; Ezaki, T.; Sanui, K.; Ogata, N. J. Appl. Polym. Sci. 1988, 35, 145. (4) Roberts, G. Langmuir-Blodgett Films; Plenum: New York, 1990. (5) Petty, M. C. Thin Solid Films 1992, 210-211, 417. (6) Tieke, B. Adv. Mater. 1991, 3, 532.
polymerizable amphiphile molecules or with preformed polymers. The polymerization of amphiphilic molecules can be realized in Langmuir or Langmuir-Blodgett films. The first study of the polymerization of amphiphilic molecules in a monolayer at the air/water interface was reported in 1935 for a maleic anhydride derivative of β-elaeostearine.8 But it was not until the 1970s that a series of polymerization reactions in monolayers had been investigated. Various reactions such as polyaddition, polycondensation, and oxidative polymerization reactions have been studied.9 Extensive studies have been carried out on the reactivity of compounds with double bonds in the hydrophilic part such as acrylic and methacrylic acid derivatives,10 long chain vinyl esters11 and styrene derivatives.12 The polymerization of unsaturated fatty acid films at the interface has also been studied.13,14 Most investigations on the polymerization in LB films have focused on the reactivity of a double bond in ω position or close to the polar head.15-18 Recently some studies on the polymerizability at the interface, or after transfer, of a molecule with a double bond in the middle of the (7) Albrecht, O.; Laschewsky, A.; Ringsdorf, H. J. Membr. Sci. 1985, 22, 187. (8) Geoffrey, G. Faraday Trans. 1936, 32, 187. (9) Tieke, B. Polymerization in Organized Media; Gordon and Breach Science Publishers: Philadelphia, PA, 1992; Chapter 2, p 105. (10) Dubault, A.; Casagrande, C.; Veyssie, M. J. Phys. Chem. 1975, 79, 2254. (11) Letts, S. A.; Fort Jr, T.; Lando, J. B. J. Colloid Interface Sci. 1976, 56, 64. (12) Leporatti, S.; Cavalleri, O.; Rolandi, R.; Tundo, P. Langmuir 1994, 10, 1334. (13) Peltonen, J. P. K.; Pingsheng, He; Rosenholm, J. B. Thin Solid Films 1992, 210-211, 372. (14) Viitala, T. J. S.; Peltonen, J.; Linden, M.; Rosenholm, J. B. J. Chem. Soc., Faraday Trans. 1997, 93, 3185. (15) Barraud, A.; Rosilio, C.; Ruaudel-Texier, A. J. Colloid Interface. Sci. 1977, 62, 509. (16) Fukuda, K.; Shibasaki, Y.; Nakara, H.; Tagaki, W.; Takahashi, H.; Tamura, S.; Kawabata, Y. Thin Solid Films 1992, 210-211, 387. (17) Laschewsky, A.; Ringsdorf, H.; Schmidt, G. Thin Solid Films 1985, 134, 153. (18) Laschewsky, A.; Ringsdorf, H.; Schmidt, G. Polymer 1988, 29, 448.
10.1021/la9809325 CCC: $18.00 © 1999 American Chemical Society Published on Web 04/29/1999
Polymerization of Aminoethyl Elaidamide
hydrocarbon chain have been reported. A good example is the case of elaidic acid, which has been polymerized in LB films under UV irradiation.19 In a previous paper,20 we reported the synthesis of a novel amphiphile which is an elaidic acid derivative. This amphiphile, N-(2-aminoethyl) trans-9-octadecenamide (aminoethyl elaidamide, AEEAm) was designed in order to elaborate on a CO2-selective composite membrane. It was synthesized from elaidic acid and ethylenediamine. It possesses like elaidic acid a double bond in the middle of the hydrocarbon chain and an amine function which is expected to react with CO2 and thus cause the selectivity. Since AEEAm is a derivative of elaidic acid, it is expected to polymerize under similar conditions. In this paper, we present the results concerning the polymerization of AEEAm by UV irradiation at the interface or after transfer on a solid support. The effects of irradiation on the Langmuir films were studied by pressure/area experiments. The irradiated films were transferred at various times of irradiation and their structure was characterized by scanning force microscopy (SFM). For Langmuir-Blodgett films, we followed the evolution of their structure by SFM during the irradiation.
Langmuir, Vol. 15, No. 11, 1999 3853
Figure 1. Evolution of area of AEEAm films at a surface pressure of 25 mN/m without irradiation (s) and during the irradiation (- -). In each cases, the area (At) was normalized by dividing by the respective initial area (A0).
Materials and Methods Aminoethyl elaidamide, AEEAm, was synthesized as described in a previous paper. Its developed formula is
Figure 2. Pressure/area isotherms of AEEAm monolayers for different irradiation times: (s) tirr ) 0 min; (- -) tirr ) 60 min; (- ‚ ‚ -) tirr ) 300 min. Chloroform and acetone were purchased from Prolabo and were used without further purification. A homemade Langmuir-Blodgett trough (dimensions 10.9 cm × 48.7 cm) was used for the monolayer formation and its transfer. It is made of PTFE and is equipped with two plunging barriers for a symmetrical compression. The surface pressure was measured using a Wilhelmy balance (R&K, Wiesbaden, Germany). The temperature throughout the experiments was 21 ( 1 °C. The water used was purified using a MILLIPORE system (Milli RO and Milli Q units) involving reverse osmosis, deionization, an active charcoal cartridge, and filtration. The pH value of the subphase was adjusted to 10.5 by adding NaOH and was measured by a pH meter (CONSORT P107). Samples were prepared by transferring films on solid supports at 25 mN/m and using the LB method with the downward speed being 10 times greater than the upward speed (1 cm/min). For the transfer, CaF2 and muscovite (mica) slides were used. CaF2 slides, obtained from Sorem (Uzos, France), were cleaned with acetone and chloroform (twice each) in an ultrasonic bath and then dried for several hours under vacuum. Muscovite samples obtained from Me´tafix (Montdidier, France) were freshly cleaved before any transfer and used without any particular processing. IR spectra of AEEAm LB films (seven layers) were obtained on a Nicolet 510 M FTIR spectrophotometer by collecting and averaging out 200 scans at a resolution of 4 cm-1. Scanning force microscopy experiments were performed with a Nanoscope II from Digital Instruments (Santa Barbara, CA) in the contact mode, with a 140 µm scanner. The cantilevers used were characterized by a low spring constant of about 0.06 N/m. All the measurements were performed in air with the feedback loop on (constant force ) 10-9-10-8 N). Langmuir Films Irradiation. AEEAm was prepared as a 10-3 M solution in chloroform (RP Normapur, Prolabo) and an amount of 0.2 mL was spread with a capillary micropipet. After AEEAm solution spreading, the pressure was brought to 25 mN/ m. Then the film was irradiated, keeping the surface pressure (19) Peltonen, J. P. K.; He, P.; Rosenholm, J. B. Langmuir 1993, 9, 2363. (20) De´rue, V.; Alexandre, S.; Huguet, J.; Deschrevel, B.; Valleton, J. M. Thin Solid Films 1997, 306, 1.
constant at 25 mN/m. The irradiation was carried out using a UV lamp (VGL-30, 2 × 15 W) with monochromatic radiation at λ ) 254 nm. The lamp was placed 15 cm above the monolayer. During the irradiation, the apparatus placed in a cabinet was flushed with a nitrogen flow. After the irradiation was stopped, the film was decompressed up to the maximum area of the trough, and we waited 40 min for the film to relax before further experiments. Then surface pressure/area isotherms were recorded by compressing the film at a constant barrier speed of 0.5 cm/ min. Samples were prepared on CaF2 for IR spectroscopy studies and muscovite (mica) substrates for SFM studies. Langmuir-Blodgett Films Irradiation. After AEEAm solution spreading, the pressure was brought to 25 mN/m, and the film was transferred by the classical LB technique at this pressure. The transfers were performed on muscovite substrates for SFM studies and on CaF2 slides for IR spectroscopy studies. The samples transferred on muscovite were glued to a mounting steel plate and positioned on the scanner of the scanning force microscope. The sample was not moved from the scanner in order to follow the effects of the polymerization in the same zone of the sample. During the UV irradiation, the UV lamp was placed over the sample at a distance of 15 cm. From time to time, irradiation was stopped and images of the sample were realized. The samples transferred on CaF2 slides were irradiated, and the evolution of the spectra was followed during the irradiation.
Results 1. Langmuir Films Irradiation. To exhibit the changes of nature of the Langmuir films during the irradiation, we performed area vs time experiments and surface pressure measurements. We also studied the evolution of the structure of AEEAm films transferred after different times of irradiation by SFM and IR spectroscopy. Area vs Time Experiments. As a reference, the area evolution of a monolayer of AEEAm monomer was studied for an imposed surface pressure of 25 mN/m (Figure 1). For this surface pressure, we observed a decrease of about 5% after 200 min showing a good stability of the monomer
3854 Langmuir, Vol. 15, No. 11, 1999
De´ rue et al.
Figure 3. SFM images of the monomer film transferred at a surface pressure of 25 mN/m onto muscovite: (a) image of a 50 µm × 50 µm zone; (b) zoom in a zone of image a. A profile of the structure of the film is shown on the bottom of each image.
film. Therefore this AEEAm film possesses interesting properties at 25 mN/m, which should favor its polymerization. The same studies were done during the UV irradiation of the AEEAm film. The curve obtained during the irradiation is different from the one obtained without irradiation. For short times, we observe a fast decrease of the area which then tends to decrease slowly in a similar way to the monomer film. This decrease suggests that a modification in the structure of the film occurred during the irradiation. This may be due to the chemical reaction which takes place at the interface. Pressure/Area Isotherms. Figure 2 shows isotherms obtained for different irradiation times (0, 60, and 300 min of UV irradiation). The monomer film shows a collapse at about 50 mN/m. At 16 mN/m, a wide plateau is observed, starting at a molecular area of 30 Å2. The plateau may be attributed to a transition from a liquid expanded phase to a more condensed phase. In this more condensed phase, a molecular area of 19 ( 1 Å2 can be estimated. After UV irradiation, the plateau disappears progressively with increasing irradiation time. These results indicate that changes in the state of AEEAm monolayer were generated by UV irradiation. Transfers have been realized on muscovite at 25 mN/m after 0, 60, and 300 min of UV irradiation in order to observe the eventual structural changes of the monolayer. IR spectroscopy. IR spectra of AEEAm films before irradiation and after 300 min of irradiation were obtained (not shown). The spectra of AEEAm films showed a peak at 964 cm-1 due to the CH wagging from the trans double bond. The peak from the double bond near 1670 cm-1 was absent from the spectra because of the quasi symmetry of the chain around the double bond. Comparing the IR spectrum of AEEAm films before irradiation with the IR spectrum of AEEAm films irradiated during 300 min, we noted that the peak at 964 cm-1 characteristic of CH wagging of double bond decreased but was still present after 300 min of UV irradiation. Therefore monomer molecules remain after long irradiation times. We estimated the percentage of reacted monomer after 300 min of irradiation to be 61%.
Scanning Force Microscopy. Figure 3 shows images of an AEEAm monomer film transferred on muscovite. A 50 µm × 50 µm SFM image of the sample (Figure 3a) shows the great heterogeneity of the LB film. The sample is characterized by high plateaus, 25 nm high (with mica as the level reference). When zooming between these plateaus, we observed that the film is constituted of globules (Figure 3b). Some bigger globules are observed as well as holes. A globular aspect is also observed for the plateaus. The presence of the holes allowed us to measure the thickness of the film. The thickness is about 12 nm and does not correspond to the thickness of a single monolayer. However according to the transfer ratio, one monolayer has been transferred. The high value of the thickness might be explained by the presence of water: some water might be entrapped inside globules of AEEAm molecules. After an UV irradiation of the monolayer over 60 min, we observed the apparition of elongated structures which are interconnected (Figure 4a). Between these structures, the film presents the same globular aspect as the monomer film. When zooming inside these elongated structures, we observed the presence of nanofibrils (Figure 4b) aligned along the main direction of the structure with average width of 16 nm. After an UV irradiation of the monolayer over 300 min, the elongated structures appeared more linear and their connection led to starlike structures (Figure 5a). A zoom at the intersection between two star branches exhibits nanofibrils (Figure 5b) aligned in the direction of each branch. These nanofibrils are similar to the ones observed in the elongated structures when the monolayer was irradiated during 60 min. On this image, the presence of alignments in the two directions proves that these nanofibrils are really characteristic of the structures and are likely induced by the polymerization. Between these starlike structures, we observed that the film had a globular aspect like the one observed for the monomer. This study showed that the irradiation led to the formation of domains and that the shapes of polymeric domains were dependent on irradiation time. We estimated the percentage of area occupied by the structures
Polymerization of Aminoethyl Elaidamide
Langmuir, Vol. 15, No. 11, 1999 3855
Figure 4. SFM images of the AEEAm film after 60 min of UV irradiation: (a) image of a 50 µm × 50 µm zone; (b) zoom inside one of these interconnected structures.
Figure 5. SFM images of the AEEAm film after 300 min of UV irradiation: (a) image of a 143 µm × 143 µm zone; (b) zoom at the intersection between two star branches.
created by the irradiation. The percentage is about 42% after 60 min of irradiation and 56% after 300 min of irradiation. These results demonstrate that the area occupied by these structures increases with the irradiation time. Therefore these structures are likely constituted of AEEAm polymerized. Furthermore the globular domains similar to the structure of the monomer film remain even after long irradiation times. These globular domains are probably composed of unpolymerized AEEAm. For irradiation times greater than 300 min, the topography of transferred films was similar to the one obtained for an irradiation time of 300 min. The percentage of area occupied by the starlike structures was estimated and is similar to the percentage obtained after 300 min of irradiation. Therefore the maximum percentage of conversion is probably already reached after 300 min. 2. Langmuir-Blodgett Films Irradiation. During the irradiation, we followed by IR spectroscopy the conversion of AEEAm monomer to polymer by measuring the decrease of the 964 cm-1 band. We also observed the topography evolution of a same zone of a AEEAm LB film at the micrometer scale by SFM. IR Spectroscopy. During UV irradiation, IR spectra (not shown) were obtained. The effects of polymerizing AEEAm by UV irradiation were important. In addition of
the gradual disappearance of the peak at 964 cm-1 characteristic of the double bond, a diminution and a broadening of the other peaks were also observed. This may be due to changes in the molecular orientation of AEEAm as polymerization proceeds. Therefore it was not possible to determine the kinetics of polymerization of AEEAm. Scanning Force Microscopy. Figure 6a represents a 30 µm × 30 µm SFM image of a AEEAm sample before irradiation as Figure 3a. We observe again high plateaus with a globular structure all over the sample. Moreover when zooming between these plateaus, we observe (Figure 6b) that the film is constituted of globules with an approximate diameter of 100 nm. The presence of the holes and some bigger globules are also observed. After an UV irradiation of the sample over 945 min, the structures observed by SFM (Figure 6c) are very similar to those observed before irradiation. The image only appears slightly more blurred than before irradiation. After 1965 min of irradiation (Figure 6d), the blurring effect is increased. However the big globules are still observed and did not move under the tip scanning constraints. The blurring effect may be explained by an increase of the interactions between the tip and the film because of the chemical changes. After 7050 min of
3856 Langmuir, Vol. 15, No. 11, 1999
De´ rue et al.
Figure 6. SFM images of the AEEAm film transferred at a surface pressure of 25 mN/m onto muscovite: (a) image of a 30 µm × 30 µm zone at t ) 0. (b-e) evolution of the topography of a 10 µm × 10 µm zone during the irradiation (b-e correspond respectively to t ) 0, 945, 1965, and 7050 min); (f) same zone as in image a at the end of irradiation (7050 min).
irradiation (Figure 6e), the structures appeared more perturbed, and the big globules are hard to observe because of the high level of tip-sample interactions which diminishes the quality of the image. The initial zone observed on Figure 6a was imaged after 7050 min of irradiation (Figure 6f) in order to determine the effect of repetitive scanning in the smaller zone. The image (Figure 6f) shows that there are few topographical changes due to UV irradiation. The high plateaus and the holes outside the scanned zone for the evolution studies have retained their shape. However in the scanned zone, changes appears more important. This is due to the
increase of the tip-sample interactions with time. The big globules are still observed at the same place as before irradiation. A slight contrast increase from the images taken before and after irradiation is observed. This contrast increase may be explained by differences in tipsample interactions. To verify that the AEEAm molecules have really polymerized in the LB film, the sample was washed with chloroform. We observed that after washing, the image of a nonirradiated film (Figure 7a) is identical to an image of bare muscovite. This indicates that all AEEAm molecules have been dissolved by chloroform. In the case of
Polymerization of Aminoethyl Elaidamide
Langmuir, Vol. 15, No. 11, 1999 3857
Figure 7. SFM images of the AEEAm film transferred at a surface pressure of 25 mN/m onto muscovite and then washed with chloroform: (a) case of a nonirradiated film; (b) case of a film irradiated over 7050 min.
the irradiated film we obtained an image (Figure 7b) in which structures corresponding to unsoluble matter are observed. This presence is a complementary proof of the polymerization process. Discussion The polymerization of the Langmuir films was demonstrated by the changes of the pressure/area isotherms, the IR results and especially by the SFM results. The irradiation of AEEAm Langmuir films led to the formation of structured domains. The shape of these domains was dependent on irradiation time and the area occupied by these domains increased with irradiation time demonstrating that these domains really correspond to the polymeric phase. After 300 min of irradiation, starlike structures were observed. A zoom in a branch of a star exhibits the presence of the nanofibrils. These nanofibrils were found to be aligned in the main direction of the branch of the star. The presence of these alignements along the main direction of the formed structure shows that the formed polymer is crystalline. Tillman et al. observed a similar phenomenon when they polymerized by UV irradiation the films of diethylene glycol diamine pentacosadiynoic amide (DPDA).21 After transfer on silicon oxide by the LB technique, they observed by SFM that the film was torn into ribbons, which after zooming appeared to be constituted of stripes aligned along the ribbons. Between these crystalline starlike structures, unpolymerized AEEAm zones remain. They are characterized by a globular morphology similar to the structure of the monomer film. This globular aspect observed by SFM has already been reported in the literature with other amphiphile films such as stearylamine22 and DPPC (1,2dihexadecanoyl-sn-glycero-3-phosphocholine) LB films, which reorganize into self-assembling vesicules.23 These globular structures are likely formed during or after transfer on a solid support. The percentage of area occupied by the starlike structures created after an irradiation time of 300 min has been estimated to be 56%. This value is in agreement with the value obtained from the IR spectra (21) Tillman, R. W.; Radmacher, M.; Gaub, H. E.; Kenney, P.; Ribi, H. O. J Phys Chem 1993, 97, 2928. (22) Lair, D. Organisation de films de Langmuir mixtes amphiphile/ glucose oxidase. Etude comparative de l’acide be´he´nique et de la ste´arylamine. The`se de l’Universite´ de Rouen, France, 1998. (23) Solletti, J. M.; Botreau, M.; Sommer, F.; Brunat, W. L., Kasas, S.; Tran Minh Duc; Celio M. R. Langmuir 1996, 12, 5379.
(61%). These IR and SFM results show that some monomer remains after long irradiation times. It must be noted that the percentage calculated from SFM images takes into account only the polymeric phase characterized by starlike structures. Some reacted monomer might be also in the “monomeric” phase characterized by a globular morphology. The presence of the reacted monomer in this phase would then explain the end of the polymerization. Indeed we can assume that changes of configuration of the double bond may be induced by the irradiation leading to the formation of isomer. Besides the presence of isomer, the presence of isolated molecules of polymer may be also suggested in the unpolymerized AEEAm domains. Rolandi et al. also observed by fluorescence microscopy such an uncomplete polymerization.24 They polymerized monolayers of surfactants functionalized with styrene groups by UV irradiation and studied the evolution of the structure of the film during the irradiation. Their fluorescence microscopy images indicated also that unpolymerized domains remained after long irradiation times. To explain this fact, the authors suggested that a side reaction could produce a dead monomer simultaneous to the polymerization process. An additional explanation is that the end of the polymerization could be linked to the growth of the polymer structures. The AEEAm film being in an organized phase at the interface, its polymerization leads to the formation of a crystalline phase as observed by SFM. The phenomenon of the crystallization which takes place probably at the same time as the polymerization may induce a modification of the molecular order of unreacted monomer. Therefore the steric requirements are no longer fulfillled and the reaction of the AEEAm polymerization stops. The maximum conversion ratio is reached after 300 min of irradiation since for times greater than 300 min, the topography of polymeric films and the percentage of reacted monomer no longer evolved. The polymerization of AEEAm in LB films was also demonstrated. By SFM, we observed the topography evolution of a same zone of a AEEAm sample at the micrometer scale during the irradiation. Few changes in the topography were revealed by SFM during the irradiation. An increase of the interactions between the tip and the sample has been observed which may be due to the (24) Rolandi, R.; Dante, S.; Gussoni, A.; Leporatti, S.; Maga, L.; Tundo, P. Langmuir 1995, 11, 3119.
3858 Langmuir, Vol. 15, No. 11, 1999
chemical changes caused by the polymerization. We realized an IR spectroscopy study of the polymerization in AEEAm LB multilayers. It was not possible to determine the kinetics of polymerization because in addition to the gradual disappearance of the CH wagging peak characteristic of the double bond, a diminution of the others peaks which may be due to changes in the molecular orientation of AEEAm as polymerization proceeds was observed. However, we demonstrated by SFM that the irradiated AEEAm films remained on the muscovite because of its unsolubility in chloroform while the non irradiated film is totally solubilized. This unsolubility is likely due to an increase in molecular weight and therefore is a proof of the polymerization of AEEAm in LB films. The LB films obtained after irradiation present a resistance toward a solvent like chloroform. This chemical stability of polymerized AEEAm film is essential for a future application. Conclusion The structures of AEEAm films irradiated at the interface or after transfer on a solid support have been studied at the micrometer scale by SFM. The originality of this study was to observe the topography evolution of these films during the irradiation. In the case of the polymerization of the LB films, we have been able to observe the topography evolution of a same zone of the sample during the irradiation. For the polymerization of AEEAm at the interface, SFM images revealed a phase separation. The shape of the polymeric domains and the area occupied by these domains were dependent on irradiation time. In the monomeric domains, reacted monomer such as isomer or isolated molecules of polymer might be also present. For the polymerization of AEEAm after transfer on a solid support, few topographic modifications were revealed by SFM
De´ rue et al.
during the irradiation. Differences of interaction between tip and sample were observed because of the chemical changes. By a simple washing process, we demonstrated that the AEEAm LB film was really polymerized. The AEEAm films were able to polymerize under different conditions. Indeed, the polymerization of AEEAm Langmuir films leads to a crystalline polymer characterized by a fibrillar morphology, and the polymerization of the AEEAm LB films leads to a noncrystalline polymer characterized by a globular morphology similar to the structure of the monomer film. These differences are due to the fact that at the interface, an ordered film was polymerized while, after transfer, a nonhomogeneous film was polymerized. For the elaboration of a composite membrane, two possibilities may be considered: the transfer of AEEAm multilayers polymerized at the interface on a porous membrane or the transfer of AEEAm multilayers on a porous membrane followed by their polymerization. In the first case, we can suggest that the transfer of polymeric AEEAm multilayers leads to an homogeneous coverage of the composite membrane by the starlike structures. However, the transfer of these polymeric films on a porous membrane may be difficult because of their rigidity. In the second case, since the support used is a porous membrane which has a structure very different from the muscovite structure, the structure of the film obtained on the membrane may be different from the one obtained on muscovite. However whatever the structure obtained after transfer of AEEAm multilayers on the membrane, we expect that the layers polymerize since we showed that the AEEAm film was able to polymerize in different conditions. LA9809325
