Phase equilibria and phase separation dynamics in a polymer composite containing a main‐chain liquid crystalline polymer

Abstract

Various topological phase diagrams of blends of main-chain liquid crystalline polymer (MCLCP) and flexible polymer have been established theoretically in the framework of Matsuyama-Kato theory by combining Flory-Huggins (FH) free energy for isotropic mixing, Maier-Saupe (MS) free energy for nematic ordering in the constituent MCLCP, and free energy pertaining to polymer chain-rigidity. As a scouting study, various phase diagrams of binary flexible polymer blends have been solved self-consistently that reveal a combined lower critical solution temperature (LCST) and upper critical solution temperature (UCST), including an hourglass phase diagram. The calculated phase diagrams exhibit liquidus and solidus lines along with a nematic-isotropic (NI) transition of the constituent MCLCP. Depending on the strengths of the FH interaction parameters and the anisotropic (nematic-nematic) interaction parameters, the self-consistent solution reveals an hourglass type phase diagram overlapping with the NI transition of the constituent MCLCP. Subsequently, thermodynamic parameters estimated from the phase diagrams hitherto established have been employed in the numerical computation to elucidate phase separation dynamics and morphology evolution accompanying thermalquench induced phase separation of the MCLCP/polymer mixture.

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

“…This implies that reorientation of LCP molecules (nematic ordering) lags behind phase separation (concentration ordering) in the blends. This observation is in agreement with the numerical results of phase separation in blends of LCP and flexible polymers 41…”

“…This observation is in agreement with the numerical results of phase separation in blends of LCP and flexible polymers. 41…”

Upper and Apparent Lower Critical Solution Temperature Branches in the Phase Diagram of Polymer:Small Molecule Semiconducting Systems

“…where the third term (C ln T term) accounts for the effect of the free volume change with temperature. 39,46 Different signs of C lead to various types of phase diagrams: a positive C gives a combined USCT and LCST or hourglass phase diagram if the UCST and LCST merge, while a negative C results in closed loop phase diagram. When C is zero, eq 2 reduces to the F−H theory of eq 1.…”

“…In addition to free volume effects, the effect of specific interactions such as hydrogen bonds may lead to LCST. 39 Conjugated materials exhibit heterointeractions via π−π stacking which is directional. This leads to anisotropy in thin films and the slightly preferred face-on texture in many semiconducting materials including PTB7-Th.…”

“…This selective, separate fit reproduces the data very well but cannot fit the phase behavior as a whole with a single functional form of χ. Modifications to the F–H theory have been proposed by various researchers that account for the relationship of the χ interaction parameter with polymer chain parameters such as molecular weight, shape, rigidity, etc. − One modified theory utilizing an equation of state of the constituent components to account for the compressibility has also been proposed that is capable of predicting not only LCST but also a concurrent UCST and LCST behavior. − With addition of a free volume term, eq can be modified to a more generalized functional form of where the third term ( C ln T term) accounts for the effect of the free volume change with temperature. , Different signs of C lead to various types of phase diagrams: a positive C gives a combined USCT and LCST or hourglass phase diagram if the UCST and LCST merge, while a negative C results in closed loop phase diagram. When C is zero, eq reduces to the F–H theory of eq .…”