The effects of processing conditions on the morphology of molecular composite films are examined by optical and electron microscopy. During coagulation processing from solutions in methanesulfonic acid (MSA), rigid‐rod polymer, such as poly(p‐phenylenebenzobisoxazole) (PBO), phase separates into undesirable aggregates. The coagulant and the method of its introduction have been found to exert a strong impact on the final film morphology. A quench of a PBO solution in MSA into a water bath results in a three dimensional interconnected network of PBO, while a slower introduction of water results in a more amorphous material. A computer simulation program of the coagulation process has been developed to better understand the different structures emerging from coagulation processing of molecular composites. The simulation results are in qualitative agreement with the experimental observations.
Kinetics of phase separation of poly(p-phenylenebenzobisoxazole) (PBO) in methanesulfonic acid are examined by the time-resolved small angle light scattering and turbidity measurements. Thin films of polymer solutions are spin-coated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo a spinodal decomposition-like phase separation, following Cahn-Hilliard type phase separation kinetics upon exposure to water vapor. An exponential increase in the scattered light intensity at short times is found. Transmittance measurements are used to determine the effects of molecular weight and coagulation medium on the rate of coagulation.
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