Scaling aspects of the kinetics of thermally induced phase separation in bisphenol A polycarbonate/poly(methyl methacrylate) blends

Phase separation in blends of bisphenol A polycarbonate and poly(methyl met hacrylate), PC/PMMA, is investigated on the microscopic scale by means of a tomic force microscopy (AFM). This technique allows the visualization of th e early stages of phase separation with greater accuracy, relative to optic al techniques. In comparison to previous data, the AFM-determined demixion vs composition curve appears to be shifted to lower temperatures. Starting from homogeneous thin films, we then follow the thermally induced spinodal decomposition process of 50/50 blends and characterize the morphological ch anges as a function of demixion time and annealing temperature. We present a quantitative investigation of the growth of the dispersed phase, based on a statistical power spectral density analysis of the AFM data. The interes t of this method is to provide information on the growth mechanism, by esta blishing the scaling relationships between the topographic roughness (which is due to phase separation), the length scale of observation, and the anne aling time. In the present case, the phase separation process appears to fo llow the Kardar-Parisi-Zhang universality class of growth, in which the den sity is not a conserved quantity. The corresponding morphology is according ly marked by a clear topographic discontinuity between the PMMA-rich domain s and the PC-rich matrix. We also observe that, at temperatures exceeding 2 20 degreesC, the late stages of the spinodal decomposition process are stro ngly affected by the occurrence of chemical reactions between PC and PMMA, which slow the growth rate of the dispersed phase and the surface roughenin g.