| dc.description.abstract | I have systematically studied the morphology and orientation of microstructures in thin films of an asymmetric poly(styrene)-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer after the thin films were subjected to solvent annealing in various vapors of nonpolar/polar cosolvents. In the first part of the thesis, I dissolved PS-b-PEO into the four solvents: toluene, benzene, tetrahydrofuran and chloroform. Each of the four solvents has a different evaporation rate. Therefore, I investigated the effect of the evaporation rate on the microphase-separated microdomains and their spatial ordering. Toluene has the slowest solvent rate. As a result, the evaporation of toluene led to hexagonal arrays of cylinders with a perpendicular orientation. On the other hand, I prepared thin films by drop casting and spin coating. It was found that drop casting couldn’t yield uniform thin films due to the coffee ring effect and that spin coating couldn’t generate microstructures with long-range ordering. Therefore, I used another coating approach, dip-coating, to prepare thin films instead. The low withdrawing rate (0.5 mm/s) induced to cylinders with a perpendicular orientation, and the high withdrawing rate (1.25 mm/s) induced to cylinders with a parallel orientation. In the second part of the thesis, I studied the morphologies in thin films after those films were subjected to solvent annealing in various solvent vapors (in mixed vapors of nonpolar/polar cosolvents). The various polar solvents in the mixed vapors were water, methanol, ethanol, 1-propanol, 1-butanol and 1-hexanol whereas the nonpolar solvent was toluene. PS-b-PEO thin films were first deposited on SiOx/Si by dip-coating at 1 mm/s from a 2 wt% toluene solution. I successfully fabricated the long range hexagonal arrays of perpendicularly-oriented cylinders upon solvent annealing thin films in the toluene/ethanol vapor of the volumetric fraction of 95/5. In addition, controling the mixed ratio of nonpolar/polar cosolvents led to complicated microphase-separated morphologies, such as the Fddd structure in the thin film with exposure to the toluene/ethanol vapor of 60/40 and the coexistence of double-gyroids and cylinders in the thin film with solvent annealing in the toluene /1-propanol vapor of the fraction of 85/15.
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