Ellipsometric studies on immiscible polymer-polymer interfaces

Abstract

Ellipsometry was employed to estimate the thickness of the interface λ between two bulk layers of dissimilar polymers. The polymer/polymer combinations investigated were poly(methyl methacrylate) (PMMA)/poly(styrene- co-acrylonitrile) (SAN) (AN content < 10 and > 33 wt%), PMMA/poly(methyl methacrylate- co-styrene) (MS) and polystyrene/MS. They provide a series of immiscible combinations with various values of the Flory interaction parameter χ ranging from 1.72 × 10 −3 to 8.71 × 10 −2. The bilayer specimen prepared by the spin-coating technique was annealed at 130°C (> T g) and the time variation of λ was observed during annealing. The observed λ attained a constant value after annealing for ∼1 h and then remained constant. The constant value was assumed to be the equilibrium thickness. The thickness ranged from ∼5 to 40 nm, depending on the magnitude of χ. The thin interface (< ∼10 nm) was nicely explained by the recent theory by Broseta et al., which deals with the effect of molecular weight on λ within the strong segregation limit.