PHASE SEPARATION MORPHOLOGY OF THIN FILMS OF POLYSTYRENE/POLYISOPRENE BLENDS

Kari Dalnoki-Veress, James Forrest, Jim Stevens and John Dutcher,
J. Polym. Sci. Part B: Polym. Phys. 34, 3017-3024 (1996).

ABSTRACT

We have studied the morphology of phase separation in thin films of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si-SiO_x), Si(001) etched in hydrofluoric acid (Si-H), and a Au-Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 100 nm thick blend films on the two Si-SiOx and Si-H surfaces as the mass fraction is varied. Smaller differences are observed between the films on the Si-SiO_x and Au/Pd surfaces only for film thicknesses h < 60 nm. It is determined that the observed morphologies are due to spinodal decomposition.

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