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구자승,Sushil Satija,이정수,서영수 한국고분자학회 2016 Macromolecular Research Vol.24 No.12
This study investigates the spontaneous formation of phase-separated bilayer structures of polymer blend thin films upon spin coating. Neutron reflectivity is used to measure the bilayer structure of deuterated polystyrene (dPS) and polymethylmethacrylate (PMMA) blend thin films with various molecular weights (Mw). The results indicate that the binary polymer blend forms a well-defined phase-separated bilayer structure of a dPS-rich layer on top of a PMMA rich layer with clear interfaces between the layers. The interfacial width is in reasonable agreement with the results of self-consistent field theory modified to account for capillary waves. The blend with higher Mw exhibits broader interfaces than the theoretical predictions, probably due to the reduced mobility of mixed polymers in the solvent during spin coating. Formation of thin blend films with parallel phase separation can provide a viable route to potential applications of the active layer in bilayer heterojunction devices for polymer photovoltaic applications.
구자승,Sushil Satija,이정수,서영수 한국고분자학회 2016 Macromolecular Research Vol.24 No.11
This study investigates the spontaneous formation of phase-separated bilayer structures of polymer blend thin films upon spin coating. Neutron reflectivity is used to measure the bilayer structure of deuterated polystyrene (dPS) and polymethylmethacrylate (PMMA) blend thin films with various molecular weights (Mw). The results indicate that the binary polymer blend forms a well-defined phase-separated bilayer structure of a dPS-rich layer on top of a PMMA rich layer with clear interfaces between the layers. The interfacial width is in reasonable agreement with the results of self-consistent field theory modified to account for capillary waves. The blend with higher Mw exhibits broader interfaces than the theoretical predictions, probably due to the reduced mobility of mixed polymers in the solvent during spin coating. Formation of thin blend films with parallel phase separation can provide a viable route to potential applications of the active layer in bilayer heterojunction devices for polymer photovoltaic applications.
Koo, Jaseung,Koga, Tadanori,Li, Bingquan,Satija, Sushil K.,Rafailovich, Miriam H. American Chemical Society 2016 Macromolecules Vol.49 No.9
<P>We investigated the effect of density fluctuation of supercritical carbon dioxide (scCO(2)) on anomalous swelling of multilayer polymer thin films On the ridge in the pressure temperature phase diagram of CO2. In order to measure the swelling ratio along the film depth, we alternatively deposited hydrogenated poly(methyl Methacrylate) (PMMA) and deuterated polystyrene (dPS) thin films and performed the neutron reflectivity measurements as a function of CO2 pressure at 36 degrees C. The results showed that, in contrast to previous studies, CO2 was to penetrate deeply:throughout the, multilayer thin film where the magnitude of swelling along the density fluctuation ridge of CO2 was independent of film thickness. Block copolymer thin films of dPS-b-PMMA with a parallel lamellar orientation also showed similar swelling behavior in scCO(2). However, it is well-known that single-layer polymer thin films exhibit anomalous swelling behavior only the film surface. This difference is probably due to the fact that the multilayer thin films have the CO2-philic PMMA layer sandwiched between dPS layers, which can function, as a CO2 reservoir, thereby transferring the CO2 molecules from the PMMA layers to the adjacent dPS layers. Furthermore, we found that the interaction between polymers and substrates was not significant in scCO(2) from diffusion dynamics results using neutron reflectivity, thereby facilitating anomalous dilation of polymers near the substrates without a pinning effect.</P>
Yang, Hosung,Shin, Kwanwoo,Tae, Giyoong,Satija, Sushil K. Royal Society of Chemistry 2009 SOFT MATTER Vol.5 No.14
<P>Poly(ethylene glycol) (PEG, 6 kg mol<SUP>−1</SUP>) terminated at both ends by a hydrophobic fluoroalkyl segment [-(CH<SUB>2</SUB>)<SUB>2</SUB>C<SUB>10</SUB>F<SUB>21</SUB>] (R<SUB>f</SUB>-PEG) has been shown to self-assemble into an essentially water insoluble hydrogel. Here, we characterize the monolayer, formed by R<SUB>f</SUB>-PEG and the subsequent adsorption of a protein, as a function of packing density at the aqueous interface by using thermodynamic methods, neutron reflectivity, and fluorescence microscopy. The <I>π</I>–<I>A</I> isotherms showed two transitions. The first transition was attributed to the start of a conformational change of PEG chains from a pancake-like shape to a stretched brush-like shape due to intermicellar packing. The second transition was assigned to a collapse of the R<SUB>f</SUB>-PEG monolayer, submerging some of the micellar R<SUB>f</SUB>-PEG underneath the monolayer and forming a multilayered state. BSA (bovine serum albumin), a model protein, adsorption onto the R<SUB>f</SUB>-PEG monolayer from the subphase was also correlated with the transition state of the monolayer. At a lower packing density below the first transition, the R<SUB>f</SUB>-PEG did not suppress BSA adsorption at all. Conversely, an almost complete prevention of BSA adsorption by the R<SUB>f</SUB>-PEG was observed once the R<SUB>f</SUB>-PEG had formed a fully-covered monolayer state.</P> <P>Graphic Abstract</P><P>The relationship between the structure of a R<SUB>f</SUB>-PEG monolayer and protein adsorption at the aqueous interface was analyzed using neutron reflectivity and <I>in situ</I> protein adsorption. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b905474j'> </P>
Jang, Yeongseon,Seo, Jooyeon,Akgun, Bulent,Satija, Sushil,Char, Kookheon American Chemical Society 2013 Macromolecules Vol.46 No.11
<P>We present the effect of molecular weight (MW) of polyelectrolytes (PEs) on the disintegration behavior of weak PE multilayer films consisting of linear poly(ethylene imine) (LPEI) and poly(methacrylic acid) (PMAA). The multilayer films prepared by the spin-assisted layer-by-layer deposition have well-ordered internal structures and also show the linear thickness growth behavior regardless of MWs of PMAA. The well-defined weak PE multilayer films were subject to disintegration into bulk solution when the electrostatic interactions between LPEI and PMAA layers were reduced by treatment at pH 2. However, we demonstrated the change in the disintegration mode and kinetics (i.e., from burst erosion to controlled surface erosion) as a function of MW of PMAA based on neutron reflectivity and quartz crystal microbalance with dissipation, revealing the correlation between the structural changes and the viscoelastic responses of the weak PE films upon pH treatment. Also, the unique swelling behavior as well as the significant increase in dissipation energy was monitored before the complete disintegration of the multilayer films containing high MW PMAA, which is believed to originate from their slow rearrangement kinetics within the film. We believe that the results shown in this study provide chain-level understanding as to the MW-dependence on pH-triggered disintegration mechanism of weak PE multilayer films.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2013/mamobx.2013.46.issue-11/ma4007736/production/images/medium/ma-2013-007736_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma4007736'>ACS Electronic Supporting Info</A></P>