Rheological behaviour of a smectic A liquid crystal under layer compression

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Abstract
We measure the apparent bulk modulus corresponding to the layer compression of a SA liquid crystal, versus the frequency of an applied strain. For thin samples, we observe an elastic regime, a high frequency internal friction resonance, and at low frequency a stress relaxation attributed to the climb of edge dislocations. For thick samples, we observe a diffusive propagation through the layers tentatively explained by a layer permeation mechanism. The estimated permeation length is in the range of 103 Å, much larger than a molecular length, and could be attributed to the glide of dislocations