Transient Wetting and 2D Spinodal Decomposition in a Binary Polymer Blend

Abstract

We have used ion beam analysis and scanning near-field optical microscopy to characterize the three-dimensional domain structure of a thin film of a phase-separating polymer mixture. In the initially mixed film, there first occurs coverage of one of its surfaces by an unbroken layer of one phase; between this -wet. surface and the substrate, layers of domains form. Eventually, the layered domain structure becomes unstable, and a transformation occurs to the equilibrium wetting state where both phases are in contact with both surfaces, causing a phase separation to be purely two-dimensional at later times. During this <<transient wetting. process, lateral and vertical domain sizes grow with time as t'/3 independent of the dimensionality of the domains.

Three-Dimensional Information on the Phase Domain Structure of Thin Films of Polymer Blends Revealed by Secondary Ion Mass Spectrometry

“…These two maps are complementary to each other because the blend phase domains created during the decomposition process form column-like structures. [1 -3] This confirms previous conclusions on the phase structure reported for other blends [17] of the PBrS/dPS system (with a different bromination fraction of PBrS).…”

“…[12,13] To determine the distributions b (x, y, z) novel quasi-three-dimensional profiling methods have been established combining the analysis of the average profile b (z) with the examination of the average lateral structures observed by various microscopic methods. [17] As not all polymer blend components provide sufficient contrast, these techniques are inherently limited in their applicability. The same is true for atomic force microscopy (AFM) combined with (not completely [18] ) selective dissolution of various film blend components.…”

Surface-directed phase separation in nanometer polymer films: self-stratification and pattern replication

“…Even for symmetric [13,50] (or weakly asymmetric [63]) interactions exerted by both external surfaces on polymer blend films, a transient self-stratification is realised for early and intermediate stages of surface-directed phase separation. However, a full self-stratification pathway leading to equilibrium bilayer morphology is possible only for antisymmetric surface-fields [3].…”

Fundamentals of Phase Separation in Polymer Blend Thin Films

“…(1.57) is c − c 0 = A(k, t) cos k · r, where k is the wavevector of a compositional variation and A(k, t) is an amplification factor depending on the wavelength, which yields 58) and therefore solutions are of the form…”

“…vertical phase separation into layers (like in figure 4.1(a); alternating layers extending into the film are also possible) occurred even when lateral phase separation (like in figure 4.1(b)) was energetically favourable. Experiments later revealed that the vertical layers forming in the non-wet regime can break up as lateral structures appear at a surface [58], with solvent evaporation experiments allowing frozen out-of-equilibrium states to be studied to investigate this breakup [59].…”