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Issue 13, 2016
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Regulating the modulus of a chiral liquid crystal polymer network by light

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Abstract

We report a novel way to modulate the elastic modulus of azobenzene containing liquid crystal networks (LCNs) by exposure to light. The elastic modulus can cycle between different levels by controlling the illumination conditions. Exposing the polymer network to UV light near the trans absorption band of azobenzene gives a small reduction of the glass transition temperature thereby lowering the modulus. The addition of blue light addressing the cis absorption band surprisingly amplifies this effect. The continuous oscillatory effects of the trans-to-cis isomerization of the azobenzene overrule the overall net cis conversion. The influence on the chain dynamics of the network is demonstrated by dynamic mechanical thermal analysis which shows a large shift of the glass transition temperature and a modulus decrease by more than two orders of magnitude. The initial high modulus and the glassy state are recovered within a minute in the dark by switching off the light sources, despite the observation that azobenzene is still predominantly in its cis state. Based on these new findings, we are able to create a shape memory polymer LCN film at room temperature using light.

Graphical abstract: Regulating the modulus of a chiral liquid crystal polymer network by light

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Publication details

The article was received on 15 Jan 2016, accepted on 13 Feb 2016 and first published on 15 Feb 2016


Article type: Paper
DOI: 10.1039/C6SM00114A
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Soft Matter, 2016,12, 3196-3201
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    Regulating the modulus of a chiral liquid crystal polymer network by light

    K. Kumar, A. P. H. J. Schenning, D. J. Broer and D. Liu, Soft Matter, 2016, 12, 3196
    DOI: 10.1039/C6SM00114A

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