Experimental evidence for the breakdown of conventional elasticity in smectics A

Abstract

Grinstein and Pelcovits have shown that anharmonic terms in the ‘microscopic’ elastic free energy lead to a qualitative change in the macroscopic elastic expressions describing the equilibrium behaviour of smectic A liquid crystals. In particular, they showed that the elastic moduli B(ω = 0,q) and K ₁ (ω = 0,q) vanish and diverge, respectively as In(q) for small wavevector q. In the dynamical case (ω ≠ 0), as predicted by Mazenko, Ramaswamy and Toner, the influence of anharmonicity is more dramatic: some viscosities diverge as 1/ω We present in this paper a finite ω version of the non-linear hydrodynamics of smectic A and what we believe to be the first experimental evidence of the decrease of the layer compressional modulus B(ω, q), at low frequency ω and wavevector q.