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Physical Society Colloquium
on the stability of the immiscible polymer/polymer interface Dr. Michele Sferrazza Rutherford Appleton Laboratory Neutron reflectivity studies of the interface between two immiscible polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), have highlighted the importance of the dispersion forces across the polymer layers in determining the interfacial width. A logarithmic dependence of the interface width on film thickness is observed, characteristic of an interface broadened by thermally induced capillary waves, whose spectrum is cut off by dispersive interactions across the polymer layer. The case of a thin PS film between air and a thick PMMA substrate - is characterised by a positive Hamaker constant, and so dispersion forces effectively stabilise the interface against thermally excited capillary waves. In the opposite case, a thin PMMA film between air and a thick PS substrate, the Hamaker constant is negative and dispersive forces destabilise interfacial capillary waves, leading to spinodal dewetting. We have studied this example of liquid/liquid spinodal dewetting, using mainly specular and off-specular neutron reflection measurements to characterise the length-scale and growth rate of the instability of the buried, polymer interfaces.
Friday, December 17th 1999, 15:30 |