Thermodynamics, Transition Dynamics, and Texturing in Polymer-Dispersed Liquid Crystals with Mesogens Exhibiting a Direct Isotropic/Smectic-A Transition

Abstract

Experimental and modeling/simulation studies of phase equilibrium and growth morphologies of novel polymer-dispersed liquid crystal (PDLC) mixtures of PS (polystyrene) and liquid crystals that exhibit a direct isotropic/smectic-A (lamellar) mesophase transition were performed for PS/10CB (decylcyanobiphenyl) and PS/12CB (dodecyl-cyanobiphenyl). Partial phase diagrams were determined using polarized optical microscopy (POM) and differential scanning calorimetry (DSC) for different compositions of both materials, determining both phase separation (liquid/liquid demixing) and phase ordering (isotropic/smectic-A transition) temperatures. The Flory-Huggins theory of isotropic mixing and Maier-Saupe-McMillan theory for smectic-A liquid crystalline ordering were used to computationally determine phase diagrams for both systems, showing good agreement with the experimental results. In addition to thermodynamic observations, growth morphology relations were found depending on phase transition sequence, quench rate, and material composition. Three stages of liquid crystal-rich domain growth morphology were observed: spherical macroscale domain growth ("stage I"), highly anisotropic domain growth ("stage II"), and sub-micron spheroid domain growth ("stage III"). Nano-scale structure of spheroidal and spherocylindrical morphologies were then determined via two-dimensional simulation of a high-order Landau-de Gennes model. Morphologies observed during stage II growth are typical of direct isotropic/smectic-A phase transitions, such as highly anisotropic "batonnets" and filaments. These morphologies, which are found to be persistent in direct isotropic/smectic-A PDLCs, could provide new functionality and applications for these functional materials.

Field-driven dynamics of nematic microcapillaries

“…Lattice-based simulations [5][6][7][8] are able resolve sub-micron domains and have mainly been applied to study the effects of sub-micron cylindrical confinement where geometry and anchoring affects the stability of the nematic phase. However, continuum simulations [12][13][14][15][16][17][18][19][20][21][22][23][24] have been able to overcome the length and timescales required to simultaneously capture defect dynamics (nanoscale) and domain shape (≥ µm).…”

Self-assembly and supramolecular liquid crystals based on organic cation encapsulated polyoxometalate hybrid reverse micelles and pyridine derivatives

“…During the cooling run of SEP-Si/PY2 assembly, the focal conic fan-shaped texture appears at 98°C (Fig. 7A), suggesting the formation of smectic A (SmA) phase [42]. The texture emerged at this temperature proves the existence of phase transition from isotropic state to LC phase, as observed in the heating run, although it was not detected by DSC.…”

Rheological Theory and Simulation of Surfactant Nematic Liquid Crystals

“…Wormlike micelle rheology is a clear example of this, and experimental results for these systems present strong similarities with lyotropic nematic polymers, including banded textures after cessation of fl ow, nonaligning -toaligning transition, damped oscillatory stress transients, and stress scaling properties of shear stress. Although not included in this review, some interesting biological manifestations, optical and biosensors, thermodynamics, converging and instabilities fl ows, bifurcations, fl uctuations of nematic liquid crystals are available in the literature (Abukhdeir and Rey, 2008 ;de Luca and Rey, 2003, 2004-c, 2007Grecov and Rey, 2003a-c, 2004Han and Rey, 1993a,b, 1994a-c , 1995aRey, 2006a,b, 2007 ;Rey, 1990Rey, , 1993aRey, ,b, 1995Rey, , 2000aRey, -c, 2001aRey, ,b, 2002Rey, , 2006Rey, , 2007Rey, , 2009Rey, , 2010Rey and Denn, 1987, 1998a-c, 2002Herrera -Valencia, 2010, 2012 ;Rey et al, 2004Rey et al, , 2005Rey et al, , 2011Singh and Rey, 1995 ;Soule et al, 2009 ;Tsuji and Rey, 1997Wang and Rey, 1997 ;Wincure and Rey, 2007 ;Rey, 2002, 2003 ;Zhou et al, 2006 ). Lastly, lyotropic chiral nematic shear rheology and texturing can also be described by the modeling methodology presented in this chapter.…”

“…The governing equations for LC fl ows follow from the dissipation function Δ (de Andrade Lima et al, 2006 ;Farhoudi and Rey, 1993a -c ;Murugesan and Rey, 2010 ;Rey 2007Rey , 2009Rey , 2010Soule et al, 2009 ):…”

“…In addition to singular defects, nonsingular defects arise in the form of lines and inversion walls (de Luca and Farhoudi and Rey 1993a -c ;Grecov and Rey, 2003a,b ;Hwang and Rey, 2006a Lhuillier and Rey, 2004a,b ;Rey, 2000aRey, -c , 2001aRey, ,b , 2007Rey, , 2009Rey, , 2010Soule et al, 2009 ;Stewart, 2004 ;Tsuji and Rey, 1988, 1997Yan and Rey, 2002 ;Zhou et al, 2006 ). Nonsingular defects are captured by the LE model since they do not involve changes in the order parameters.…”