Liquid crystal foam
Seminar Room 1, Newton Institute
AbstractWe investigate whether a liquid crystal foam, made by shearing an ionic mesogen, exhibits the same properties as an ordinary liquid foam. In particular, for a quiescent foam we find: (i) where three walls meet, they do so at approximately 120-degree angles, for all times studied; (ii) Lewisís law of linear relation between cell area and number of sides is approximately satisfied at late times; (iii) the morphological patterns coarsen in time, both T1 and T2 processes are observed and, at late times, evolution is consistent with von Neumannís law; and (iv) relatively large numbers of 5-sided cells survive up to fairly late times. Results (i) and (iii) suggest that surface tension may play a key role in determining the physics of this system, as it does in low-viscosity liquid foams. If our mesogen is subjected to controlled shear, there is a threshold shear rate below which no foam can form. Above this threshold, a steady-state foam pattern is obtained where the mean cell area generally decreases with increasing shear rate. Furthermore, the steady-state internal cell angles and distribution of cell number of sides deviate from their equilibrium (i.e. zero-shear) values.
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