Abstract
On the basis of the major application for block copolymers to use them as separation membranes, lithographic mask, and as templates, the preparation of highly oriented nanoporous thin films requires the selective removal of the minor phase from the pores. In the scope of this study, thin film of polystyrene-block-poly(ethylene oxide) block copolymer with a photocleavable junction groups based on ortho-nitrobenzylester (ONB) (PS-hν-PEO) was papered via the spin coating technique followed by solvent annealing to obtain highly-ordered cylindrical domains. The polymer blocks are cleaved by means of a mild UV exposure and then the pore material is washed out of the polymer film by ultra-pure water resulting in arrays of nanoporous thin films to remove one block. The removal of the PEO materials from the pores was proven using the grazing-incidence small-angle X-ray scattering (GISAXS) technique. The treatment of the polymer film during the washing process was observed in real time after two different UV exposure time (1 and 4 h) in order to draw conclusions regarding the dynamics of the removal process. In-situ X-ray reflectivity measurements provide statistically significant information about the change in the layer thickness as well as the roughness and electron density of the polymer film during pore formation. 4 H UV exposure was found to be more efficient for PEO cleavage. By in-situ SFM measurements, the structure of the ultra-thin block copolymer films was also analysed and, thus, the kinetics of the washing process was elaborated. The results from both measurements confirmed that the washing procedure induces irreversible change in morphology to the surface of the thin film.
Highlights
The production of nanoporous materials have attracted tremendous interest due to their immense application in variety of fields, including separation, catalysts, biomaterials engineering, Polymers 2020, 12, 781; doi:10.3390/polym12040781 www.mdpi.com/journal/polymersPolymers 2020, 12, x FOR PEER REVIEW and electronics [1,2,3]
Highly-ordered thin films is one of the outstanding outstanding fields of research in the context of block copolymers since they enable a versatile selffields of research in the context of block copolymers since they enable a versatile self-assembled assembled morphology range nm of byameans of a “bottom-up”
The out-of-plane scan cuts were performed along the wavevector q y direction on the 2D grazing-incidence small-angle X-ray scattering (GISAXS) patterns to extract one-dimensional (1D) scattering profiles in order to detect the formation of nanodomains of the photocleaved polymer thin films and the distance between the cylindrical PS domains
Summary
The production of nanoporous materials have attracted tremendous interest due to their immense application in variety of fields, including separation, catalysts, biomaterials engineering, Polymers 2020, 12, 781; doi:10.3390/polym12040781 www.mdpi.com/journal/polymers. Several methods for the removal of one block out of a thin film have been reported, several methods for the removal of one block out of a thin film have been reported, such as chemical such as ozonolysis, chemical etching, ozonolysis, and UV degradation. Overall, they under can only be etching, hydrolysis, and UVhydrolysis, degradation. In thin polymer films, the swelling polymer films, thesensitive swellingtodynamics areinvery sensitive to the interaction the dynamics are very the changes interaction within thechanges system.inThis plays an within important system.
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