Study of Ordered Macroporous Polymer Films by Templating Breath Figures
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Study of Ordered Macroporous Polymer Films by Templating Breath Figures Lulu Song 193 pages Directed by Dr. Mohan Srinivasarao Macroporous films with highly ordered pore patterns have many potential applications. Some examples include microstructured electrode surfaces, photonic band gap materials and filters for cell sorting and bio-interfaces. In this dissertation we discuss a moist-casting method to prepare hexagonally-ordered macroporous films with pore sizes in the range of sub-micron to several microns, where condensed water droplets (breath figures) work as templates. Compared with other templating methods, this one is fast and simple. Well-ordered porous films can be obtained in tens of seconds and the pore size can be easily tailored and dynamically controlled by adjusting the casting conditions. More importantly, there is no need to remove the templates; water droplets just evaporate when the casting processes are finished. This study was carried out with the intention of characterizing the structures, understanding film-formation processes and exploring special properties and possible applications. For the structural characterization, film morphology was studied in detail by normal optical microscopy and laser scanning confocal microscopy (LSCM). Several interesting features have been revealed. Meanwhile, the degree of the order of the porous structures were characterized both in real space via Voronoi diagram and bond-orientational correlation function, and in reciprocal space via Fraunhofer diffraction pattern. To further understand the mechanism, the evaporation of the polymer solutions during the film formation was studied by monitoring their mass over time. Besides, the evolution of breath figures formed on the evaporating polymer solutions was in-situ recorded via a high-speed camera coupled to an optical microscope. Combined with the information on the film structures obtained via LSCM, explanations for some detailed features have been attempted. Wetting property of these films was studied in some detail. The films exhibited lotus effect, mimicking natural non-wetting surfaces. To improve the solvent stability and mechanical properties of the macroporous films for possible applications, crosslinking of the polymer matrix was tried by heating. Crosslinked structures with hexagonal arrays of cone-like air holes were obtained, which might find use as micron-sized beakers for small-quantity analysis.