Characterizing Interface Shape Evolution in Immiscible Polymer Blends via 3D Image Analysis

Abstract

The coordinate transformation (CT) method was applied to measure the local curvature of the interface of an immiscible polymer blend made of fluorescently labeled polystyrene (FLPS) and styrene-ran-acrylonitrile copolymer (SAN). The CT method involves the local parametrization of the interface by a quadratic polynomial to compute the local values of the mean (H) and the Gaussian (K) curvatures. Distributions of the curvatures at different annealing times were obtained by measuring H and K at many (typically 10(7)) points on the interface. Coarsening of a symmetric (50/50 w/w FLPS/SAN) and a nonsymmetric (35/65 w/w) blend was monitored. For the symmetric blend, two regimes of surface evolution were identified: in the early stage, the probability densities of the curvatures at various times were successfully scaled by a time-dependent characteristic length, i.e., interface area per unit volume (Q). This behavior has been previously observed in blends with morphologies created by a different mechanism, namely spinodal decomposition. In the late stage, the dynamic scaling failed and the time evolution of the interface slowed down. For the nonsymmetric blend, the domains of the minor phase (FLPS) were more elongated and they eventually broke up producing a composite microstructure with islands of drops within cocontinuous domains. We defined a "scaled" genus (G) to quantify the topology evolution of the blends during coarsening. Loss of connectivity was evidenced by a decrease of G with time for the nonsymmetric blend, while a constant value of this parameter indicated no change in topology during coarsening for the symmetric blend.

A framework for interpreting the coarsening and structural evolution of two co‐continuous immiscible viscous fluids

“…Notwithstanding the significant differences in how these co‐continuous systems are formed, there is substantial evidence that the underlying topology of systems produced by phase separation and by mechanical mixing is similar. Lopez‐Barron and Macosko found that the appearance and the hyperbolic interfacial curvature distributions of low interfacial tension, (less than roughly 2 mN/m) co‐continuous fluid systems prepared by mechanical mixing are similar to those measured in the late stages of spinodal decomposition . It is also worth noting that the curvature distribution of mechanically mixed systems shifts toward having a less hyperbolic and more parabolic character as interfacial tension increases …”

“…Furthermore, experimentally measured and dynamically scaled mean and Gaussian curvature distributions for these systems are super‐imposable on single master curves consistent with self‐similar coarsening throughout this linear coarsening regime . In addition, Lopez‐Barron computed the genus/volume as a function of time for one system at two phase volume fractions and found it fell continuously with time. The genus is an important topological feature which represents the number of holes in a surface.…”

“…The genus is an important topological feature which represents the number of holes in a surface. It is computed from the area integral of the local Gaussian curvature measured over a volume large enough to contain a statistically representative area of interface (see Lopez‐Barron for methodology). In the context of co‐continuous fluid structures, it is a measure of the level of interconnectivity of the structure which falls continuously in the linear coarsening regime.…”

Suppressing phase coarsening in immiscible polymer blends using nano-silica particles located at the interface

“…This is usually attributed to the formation of a hydrodynamically percolated particle network of the lled particles. [43][44][45] However, upon annealing, the coarsening process differs very much for pure blend and the particle lled blends. For 50/50 PP/PS blend with co-continuous morphology, all the interface of the two phases are practically connected and form a channel throughout the blend.…”

Feather‐like morphology of poly(methyl methacrylate)/poly(ethylene oxide) blends: The effect of cooling rate and poly(methyl methacrylate) content

“…Thus, the blends also can be divided into another three kinds: miscible, immiscible, and partially miscible blends. The miscibility of blends has been widely studied . Wu points out that the integrated crystallization behavior occurs in the immiscible systems because of the macrophase separation of blends.…”