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Issue 30, 2019
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Isotropic–isotropic phase separation and spinodal decomposition in liquid crystal–solvent mixtures

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Abstract

Phase separation in mixtures forming liquid crystal (LC) phases is an important yet under-appreciated phenomenon that can drastically influence the behaviour of a multi-component LC. Here we demonstrate, using polarising microscopy with active cooling as well as differential scanning calorimetry, that the phase diagram for mixtures of the LC-forming compound 4′-n-pentylbiphenyl-4-carbonitrile (5CB) with ethanol is surprisingly complex. Binary mixtures reveal a broad miscibility gap that leads to phase separation between two distinct isotropic phases via spinodal decomposition or nucleation and growth. On further cooling the nematic phase enters on the 5CB-rich side, adding to the complexity. Significantly, water contamination dramatically raises the temperature range of the miscibility gap, bringing up the critical temperature for spinodal decomposition from ∼ 2 °C for the anhydrous case to >50 °C if just 3 vol% water is added to the ethanol. We support the experiments with a theoretical treatment that qualitatively reproduces the phase diagrams as well as the transition dynamics, with and without water. Our study highlights the impact of phase separation in LC-forming mixtures, spanning from equilibrium coexistence of multiple liquid phases to non-equilibrium effects due to persistent spatial concentration gradients.

Graphical abstract: Isotropic–isotropic phase separation and spinodal decomposition in liquid crystal–solvent mixtures

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Article information


Submitted
06 May 2019
Accepted
11 Jun 2019
First published
14 Jun 2019

Soft Matter, 2019,15, 6044-6054
Article type
Paper

Isotropic–isotropic phase separation and spinodal decomposition in liquid crystal–solvent mixtures

C. G. Reyes, J. Baller, T. Araki and J. P. F. Lagerwall, Soft Matter, 2019, 15, 6044
DOI: 10.1039/C9SM00921C

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