Director libration in nematoacoustics

We extended the analysis of a variational theory for nematoacoustics recently proposed by Virga [Phys. Rev. E 80, 031705 (2009)] by allowing the nematic director to vibrate about an average orientation at the frequency of a propagating wave, a periodic motion that we call the director libration. The acoustic susceptibilities, two phenomenological parameters that, in this theory, express the coupling between director and acoustic fields, are estimated along with an extra viscosity coefficient by using available experimental data.