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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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Publication details

The article was received on 06 May 2019, accepted on 11 Jun 2019 and first published on 14 Jun 2019


Article type: Paper
DOI: 10.1039/C9SM00921C
Soft Matter, 2019,15, 6044-6054

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    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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