Dewetting and phase separation in polymer thin films

Qi Pan, University of Pennsylvania

Abstract

In this thesis, dewetting of polymer/polymer bilayers and phase separation in polymer blend thin films are investigated to understand the effects of film thickness and substrate type on the film stability. The kinetics of dewetting a polycarbonate (PC) film from a poly(styrene-co-acrylonitrile) (SAN) film deposited on a silicon substrate is studied at 180$\sp\circ$C. Using video-optical microscopy (OM), the hole velocity, V, is constant for a PC thickness, H, of 200 nm but increases with time for H = 310 nm. In both cases, V increases linearly with SAN thickness, L, then becomes constant for L $>$ 1000 nm. In contrast to liquid/liquid theories, detailed morphology analysis by atomic force microscopy (AFM) finds the hole rim to be asymmetric and the resulting rim velocity field to be non-uniform. The SAN thickness within the hole is found to be lower than the original SAN thickness, in agreement with the equilibration of hydrostatic and dynamic pressures. Phase separation in rigidly confined polymer films of polystyrene (PS) and poly(vinyl methyl ether) (PVME) with 0.30 volume fraction of PS is also studied. Using OM to monitor morphology, the PS-rich minority phase is observed to grow anisotropically under confinement. The phase separation displays evolution and pseudo-equilibrium stages. With decreasing film thickness, phase evolution becomes faster because of the preferential wetting of the PVME-rich phase at the substrate. Also, the pseudo-equilibrium area fraction of the PS-rich phase, A$\rm \sb{p},$ decreases linearly due to spatial confinement. When compared with the results in glass-confined films, phase separation in gold-confined films evolves faster and reaches a larger A$\rm \sb{p}.$ Films of deuterated polystyrene (DPS) and PVME with 0.30 volume fraction of DPS deposited on silicon are also studied. Because of the deformable air/film interface a slower phase evolution and larger pseudo-equilibrium phase size are observed. In contrast to the confined films, the DPS-rich minority phase grows out of the film resulting in a surface roughening transition.

Subject Area

Materials science|Plastics

Recommended Citation

Pan, Qi, "Dewetting and phase separation in polymer thin films" (1996). Dissertations available from ProQuest. AAI9627980.
https://repository.upenn.edu/dissertations/AAI9627980

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