TCM
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Mark Warner

Prof Mark Warner

Prof Mark Warner FRS

Fellow of Corpus Christi College

Office: 505 Mott Bld
Phone: +44(0)1223 3 37380
Email: mw141 @ cam.ac.uk
Personal web site

TCM Group, Cavendish Laboratory
19 JJ Thomson Avenue,
Cambridge, CB3 0HE UK.

Collaborations

Co-director, isaacphysics Project

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Research

Novel solids having the directional order of liquid crystals (LCs). Such solids derive from

The unusual mechanics of LC solids includes:

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In Plain English

In the Hookean, elastic classification of the states of matter of the 1670s, gases take the volume (V) and shape (S) of their container, liquids require energy to change V but S is free, and solids require energy to have V and S changed.

Even "oddities" fit into these categories; glass has well-defined V and S, as does rubber though S is weak while V is strong. Liquid crystals will flow and are liquids, despite being anisotropic about a (mobile) director.

But Hooke's scheme is not complete: Rubber is a weak solid because it is molecularly mobile like a liquid. Combination with liquid crystals gives liquid crystal elastomers -- weak, rubbery solids with mobile anisotropy. They respond to some imposed S-changes by rotating their their anisotropy of molecular elongation. They then macroscopically extend without distorting their molecular distribution. This subset of all shape changes have no accompanying rise in energy. Hooke would have called these shape changes liquid-like. We call them "soft elasticity". They dominate, and make very rich, the mechanics of these new materials.

One can switch off the anisotropy and underlying elongation of liquid crystal elastomers (and of their strong, glassy relatives) by heating or by light, if dye molecules are present. There is a macroscopic shape change of up to 400% that is reversed on cooling or darkness. This too is unknown in mechanics. Light is a particularly beautiful way to drive mechanics. It can be delivered remotely, quickly, and the mechanics is polarisation sensitive. Defects in the pattern of anisotropy, especially in glassy LC solids, lead to changes in topography and even in topology of solid sheets.

We are also exploring exploitation of these new, rule-breaking phenomena for actuation, energy recovery, medical devices, chiral separation, . . .