Nematic Order Drives Phase Separation in Polydisperse Liquid Crystalline Polymers

Abstract

In a polydisperse thermotropic main-chain liquid crystalline polymer, we observe the process of thermally induced nematic−nematic phase separation between short and long polymer chains. We study the dynamical features of this system, in particular the evolution of Schlieren textures formed by disclinations surrounding areas of relatively uniform director. We analyze the dependence of domain size ξ on temperature and the nematic order parameter, and the evolution of textures with the waiting time at a temperature well below the nematic transition T ni. We find that before phase separation the coarsening proceeds toward the uniform state, with characteristic size of the texture increasing as ξ ∼ t 1/4. When the system is phase-separated, the texture in the regions with long chains is frozen at an equilibrium value ξ, a reversible function of temperature, while in the short-chain regions the coarsening accelerates. This behavior is interpreted in terms of a miscibility gap that is proportional to the degree of nematic order, which is different for the different lengths of the nematic polymers.

Long‐range orientation correlations and molecular alignment in sheared thermotropic copolyester. In situ light and X‐ray scattering

“…The average distance between these microregions represents the size within which the director is more or less aligned, and is a characteristic length scale of the texture. 35,44,45 However, the texture in the director field is energetically unfavorable and it is penalized by the Frank elastic energy density 1=2½K Á ðrnÞ 2 . Therefore, in unconstrained conditions the texture would relax towards an equilibrium uniform director alignment.…”

Molecular heterogeneity drives reconfigurable nematic liquid crystal drops

“…Evidently, the surface tension in drops with pure macromer is too large to permit shape transitions, presumably due to poor anchoring at the surface 33 . Moreover, the macromeronly system viscosity is much larger 23 than the drops with smaller average chain length, making texture formation/reformation kinetics very slow.…”

“…See Methods for these latter experiments. Previously, shape transitions were observed in molecularly heterogeneous systems 20 , and the phenomenon of segregation by size, broadly defined, has been reported in lipid membrane systems 21 , near topological defects in LC simulations 22 , and in LC polymer systems mediated by size-dependent nematic/isotropic-transition temperatures 23 . It is perhaps useful to reconsider these phenomena in light of our experiments.…”

Mimicry of a biophysical pathway leads to diverse pollen-like surface patterns

“…We further explore the interplay between surface energy and phase transition by examining the effect of LCO chain length polydispersity. In general, mixtures of heterogeneous chain lengths tend to phase-separate (25,26). LCOs synthesized by free-radical-mediated click reactions (27) (SI Appendix, Fig.…”

“…As <l> increases, longer chains aggregate to regions of smaller mean curvature. The difference in T NI serves as the thermodynamic driving force for phase segregation of different chain length LCOs (25). Presumably, shorter-chain LCOs tend to concentrate to the central hedgehog defect area with high elastic deformation (29,30), whereas longer-chain LCOs aggregate toward the interface, flattening out the divots.…”