Gelation Impairs Phase Separation and Small Molecule Migration in Polymer Mixtures

Abstract

Surface segregation of the low molecular weight component of a polymeric mixture is a ubiquitous phenomenon that leads to degradation of industrial formulations. We report a simultaneous phase separation and surface migration phenomena in oligomer–polymer ( O P ) and oligomer–gel ( O G ) systems following a temperature quench that induces demixing of components. We compute equilibrium and time varying migrant (oligomer) density profiles and wetting layer thickness in these systems using coarse grained molecular dynamics (CGMD) and mesoscale hydrodynamics (MH) simulations. Such multiscale methods quantitatively describe the phenomena over a wide range of length and time scales. We show that surface migration in gel–oligomer systems is significantly reduced on account of network elasticity. Furthermore, the phase separation processes are significantly slowed in gels leading to the modification of the well known Lifshitz–Slyozov–Wagner (LSW) law ℓ ( τ ) ∼ τ 1 / 3 . Our work allows for rational design of polymer/gel–oligomer mixtures with predictable surface segregation characteristics that can be compared against experiments.

Canonical Simulation Methodology to Extract Phase Boundaries of Liquid Crystalline Polymer Mixtures

“…A brief overview of our model [33], used for both the polymer (A) and liquid crystal species (B), is given in this section for reference, including how it is extended to control the rigidity of the model mesogens. The bonded interactions between coarse-grained beads for both species are described using the FENE potential [34],…”

Thermodynamics predicts a stable microdroplet phase in polymer–gel mixtures undergoing elastic phase separation

“…See DOI: 10.1039/cXsm00000x/ background matrix that alters the thermodynamics of phase separation [11][12][13] . Recent experiments on mixtures of liquid PDMS and fluorinated oil in a matrix of cross-linked PDMS show the dependence of the droplet size on the nucleation temperature and the network stiffness 14,15 .…”

Wetting Behavior of a Three-Phase System in Contact with a Surface

“…Additionally, residual elastic interactions in the matrix arising from the presence of cross-links are known to severely modify free-energy landscapes of bulk mixtures and thus affect surface migration and wetting behavior. 23 …”

“…Additionally, residual elastic interactions in the matrix arising from the presence of cross-links are known to severely modify free-energy landscapes of bulk mixtures and thus affect surface migration and wetting behavior. 23 In this paper, we present a consistent mean-field treatment of the thermodynamics of wetting for a two-component, threephase system, which is in contact with an external surface, which acts as a spectator. The free energy of such a class of systems is modeled initially by two order parameters, (i) one distinguishing between the ordered and disordered phases and (ii) one that distinguishes between two disordered phases differing in density.…”