EXPERIMENTAL-EVIDENCE FOR THE BREAKDOWN OF CONVENTIONAL ELASTICITY INSMETCTICS-A

Grinstein and Pelcovits have shown that anharmonic terms in the 'micro scopic' elastic free energy lead to a qualitative change in the macros copic elastic expressions describing the equilibrium behaviour of smec tic A liquid crystals. In particular, they showed that the clastic mod uli B(omega = 0,q) and K1(omega = 0,q) vanish and diverge, respectivel y as In(q) for small wavevector q. In the dynamical case (omega not-eq ual 0), as predicted by Mazenko, Ramaswamy and Toner, the influence of anharmonicity is more dramatic: some viscosities diverge as 1/omega. We present in this paper a finite omega version of the non-linear hydr odynamics of smectic A and what we believe to be the first experimenta l evidence of the decrease of the layer compressional modulus B(omega, q), at low frequency omega and wavevector q.