Phase Separation in Binary Polymer/Liquid Crystal Mixtures:  Network Breaking and Domain Growth by Coalescence-induced Coalescence

Abstract

A small-angle light scattering (SALS) technique together with optical microscopy observation are used to investigate phase separation kinetics in films of low molecular weight thermotropic liquid crystal (4-cyano-4'-n-octyl-biphenyl, 8CB) with flexible polymer (polystyrene, PS). The growth of domains is studied as a function of time, film thickness, and film composition. The light scattering results are correlated with the images obtained by optical microscopy observation. In this paper, we study the breaking of a bicontinuous network of polymer in liquid crystal into droplets and their further growth via the coalescence-induced coalescence mechanism. The appearance of droplets in the system leads to a strong scattering at small wave vectors, while the bicontinuous network gives a peak at a nonzero wave vector. Superposition of these scattering intensities leads to the appearance of a second peak in the full scattering intensity signal, when the bicontinuous network starts to break up into disjointed elongated domains. Finally, both peaks merge into a single peak, which moves quickly toward zero wave vectors, indicating a complete transformation of elongated domains into spherical droplets of variable size. We found that the separation process does not depend on the size of the system. Irrespective of the sample thickness, the network breaks into fragments always at the same time after temperature quench. On the basis of morphological analysis, we found that the average size of the droplets which formed from the network grows with time, t, as t(alpha), alpha = 0.9 +/- 0.1, in the isotropic phase and in the nematic phase.

One step preparation of superhydrophobic polymeric surface with polystyrene under ambient atmosphere

“…It is probably that, the large kinetic energy barrier for high molecular weight polymer ceases the phase separation in the PCT regime. Only the solution temperature increases enough and accelerates the relaxation of long chains greatly at the early stage of phase separation, the resultant compact structure reduces the apparent CA slightly [25][26][27]. From discussion above, it indicates the dendritic percolation structure can be easily obtained by selecting the appropriate solvent and molecular weight on the basis of phase demixing at PTC transition.…”

“…Generally, phase separation can be divided three regimes: (i) the percolation regime, (ii) the PCT regime and (iii) the cluster regime. The different regimes would present different microstructure, and a large kinetic energy barrier proportional to degree of polymerization could freeze the phase separation in the PTC regime with percolating network structure [25][26][27]. To prove it, the low-molecular-weight PS was also chosen and its cast-coated surface was composed of spheres ranging from 1 to 4 µm in diameter as shown in Fig.…”

A Facile Method for Preparing Sticky, Hydrophobic Polymer Surfaces

“…The spinodal decomposition process is generally divided into three regimes: (1) a percolation regime, where a bicontinuous structure is formed; (2) a percolation-to-cluster transition regime, where the polymer fibrils break up into discrete domains; and (3) a cluster regime, where the domains grow. ,, Different structures are observed in each regime, and the kinetics of the evolution process is influenced by the degree of polymerization of the polymer.…”

Dynamics of Phase Separation in Polymer Blends Revisited: Morphology, Spinodal, Noise, and Nucleation

“…Finally, we would like to point out that CHC model with FHG free energy is not suitable to describe the final stages of phase separation without proper account of hydrodynamic flows 52–54. It has recently been demonstrated55–57 in experiments and that in late stages of phase separation when the bicontinuous network breaks into droplets (which must occur either due to the finite size effect or due to the wetting properties of the bounding walls) the system evolves according to the coalescence‐induced coalescence mechanism 52–54. In this mechanism any process of domains coalescence induces hydrodynamic flow, which pushes other domains towards each other and induces further coalescence events.…”