Equilibrium phase behavior of polymer and liquid crystal blends

Abstract

A theoretical framework describing the equilibrium phase behavior of polymers and liquid crystals is presented. Linear and crosslinked polymers are considered, and complexities found in the phase properties of systems involving crosslinked networks are highlighted. Effects of the rubber elasticity parameters in the elastic free energy are found to induce substantial distortions in the phase diagram. The Flory‐Huggins interaction parameter which governs the miscibility of the mixture in the isotropic state is assumed to be independent of the polymer architecture and modeled either by using a function of temperature only or temperature and composition. The thermodynamic description of the ordered domains is made according to the Maier‐Saupe theory for nematic order and its extension to include other ordering properties. In particular, the smectic‐A order is described according to the generalization of the Maier‐Saupe theory proposed by McMillan. In the presence of nematogens, the coupling leads to quite different phase properties. In the strong coupling limit, a wide single nematic phase is found. In the weak coupling, the miscibility gap is much wider. These mixtures are described with mean‐field theories of nematogen first developed by Brochard et al. and later extended by Kyu et al. This theoretical formalism has been applied successfully to analyze data obtained on several systems including linear and crosslinked polymer networks, smectic and nematic low molecular weight liquid crystals (LMWLC), and nematogen mixtures.

Swelling of crosslinked polyacrylates in isotropic and anisotropic solvents

“…In the isotropic region above T NI , a first-order volume phase transition was found. We also reported similar results 27,28 . In this article, we go along these lines and give data analyzed within an extension of the previous theoretical treatment to the case of LMWLCs.…”

“…On the basis of these considerations, one can calculate the phase diagram using the standard procedure of chemical potentials described previously. 27,28 A theoretical fit of data gave us the parameter as a function of temperature for each system studied. Consistent with Flory's mean field approach, the affine deformation model yields the elastic parameters ␣ ϭ ␤ ϭ 1 and takes into account the difunctionality of the crosslinker.…”

“…This work can be viewed as part of the systematic studies undertaken in our laboratory to explore the physical properties of composite materials made of polymers and LMWLCs such as polymer-dispersed liquid crystals (PDLCs). [27][28][29][30] Two main problems emerge when one deals with these materials with regard to their performances in terms of aging, thermal stability, mechanical strength, electrooptical responses, and relaxation processes. The miscibility of molecular constituents in the precursor mixture is the first problem.…”

Modeling Phase Separation of Free-Radical Polymerizations in Crosslinked Networks

“…This behavior can create spatial variation in the composition of the final material. Although controlled PIPS is desirable, particularly for the fabrication of porous membranes, unanticipated inhomogeneities limit performance. , For applications where increased mechanical properties are desired, spatial inhomogeneities create sites of different mechanical properties where fracture propagation and premature failure occurs. For optical applications, inhomogeneities can form light-scattering loci and regions of mismatched refractive index, causing the onset of haze and limiting optical transmission.…”

Phase Properties of Interpenetrating Polymer Networks and Liquid Crystals

“…Benmouna et al [12][13][14] performed a study on the theoretical phase diagrams of mixtures of cross-linked polymers and the commercial LC blend E7. Substantial differences were observed as compared to the case where the polymer components are made of linear chains.…”