Jumping In and Out of the Phase Diagram Using Electric Fields: Time Scale for Remixing of Polystyrene/Poly(vinyl methyl ether) Blends

Anisotropic remixing of a phase separated binary colloidal system with particles of different sizes in an external modulation

We explore the phase behavior of a binary colloidal system under external spatially periodic modulation. We perform Monte Carlo simulations on a binary mixture of big and small repulsive Lennard-Jones particles with a diameter ratio of 2:1. We characterize structure by isotropic and anisotropic pair correlation functions, cluster size distribution, bond angle distribution, order parameter, and specific heat. We observe the demixing of the species in the absence of external modulation. However, the mixing of the species gets enhanced with increasing potential strength along with the alignment of the particles transverse to the modulation. The de-mixing order parameter shows discontinuity with increasing modulation strength, characterizing a first order phase transition. The peak in specific heat increases linearly with the size of the system. We also look into the dynamical behavior of the system via computing Mean Square Displacement (MSD) along both parallel and perpendicular directions to the modulation. We observe a decrease in the diffusion coefficient for both types of particles as we increase the strength of the modulation.

Anisotropic phase-separated morphology of polymer blends directed by electrically pre-oriented clay platelets

We describe a general pathway to prepare an anisotropic phase-separated polystyrene (PS) - poly(vinyl methyl ether) (PVME) blend morphology by using electrically pre-orientated clay platelets. The clay platelets were oriented in a PS/PVME blend by means of an externally applied AC electric field while the blend is in one phase. Following orientation step, phase separation of the blends was induced by a temperature jump above their lower critical solution temperature (LCST) in the presence of the oriented clay platelets. In this process, an early stage co-continuous PS/PVME morphology coarsened and turned anisotropic phase-separated morphology parallel to the direction defined by clay planes oriented by AC electric field. The degree of anisotropy of PS/PVME phase-separated morphology was characterized by image analysis and that was found to be linearly proportional to the degree of orientation of clay platelets obtained by a 2D Wide Angle X-ray Scattering (WAXS). Transmission Electron Microscope (TEM) image of the blend morphology revealed that clay platelets oriented to AC field direction were located in a PVME phase. The electrically ordered column structures of clay platelets in the PVME phase yielded anisotropic PS diffusion during the phase separation. This process provides a unique new way to develop directionally organized phase-separated morphology from partially miscible binary blends using nanoparticles in combination with an external electric field.

Liquid-liquid criticality in the dielectric constant and refractive index: A perspective

The critical region in the phase diagram of condensed matter systems such as fluids or fluid mixtures is characterized by the anomalous behaviour of specific thermodynamic properties. Here, we discuss the progress of understanding the behaviour of two intimately related properties, the dielectric constant [Formula: see text] and the refractive index n, when approaching the liquid-liquid critical point in binary liquid mixtures. Phenomenological scaling approaches, in particular, complete scaling formulation, are highlighted. In addition, experimental evidence provided by dielectric spectroscopy and optical measurements supporting the asymmetry-related critical features in [Formula: see text] and n in the one- and two-phase regions is assessed. We revisit recent experimental data and point out peculiar patterns of behaviour of polar-polar liquid mixtures as compared to (much more frequently studied) polar-non-polar mixtures. We point the necessity of additional research efforts towards the study of polar-polar mixtures, which would shed light into the influence of (microscopic) system-dependent parameters on asymmetry-related features of liquid-liquid criticality.

Interface Repulsion and Lamellar Structures in Thin Films of Homopolymer Blends due to Thermal Oscillations

In equilibrium the interface potential that describes the interaction between two AB interfaces in a binary blend of A and B homopolymers is attractive at all distances, resulting in coarsening of the blend morphology even in the absence of interface curvature. We demonstrate that the dissipative assembly in response to a time-periodic variation of the blend incompatibility qualitatively alters this behavior; i.e., for suitable parameters the interface potential exhibits a periodic spatial modulation and AB interfaces adopt a well-defined distance. We explore for which oscillation periods and amplitudes an interface repulsion occurs and demonstrate that we can control the preferred interface distance over a wide range by varying the oscillation period. Using particle-based simulations we explicitly demonstrate that this dissipative assembly of a homopolymer blend results in a lamellar structure with multiple planar interfaces in a thin film geometry.