Interfacial energy for nematic liquid crystals : beyond the spherical approximation

Elestic constants in the interfacial layer at the nematic-liquid-crystal-vapour interface

“…We will show that, in the general case, there are five contributions that coincide with the standard Frank-0seen elastic constants Kll, K22 and K~ and the two surface-like Nehring-Saupe elastic constants K13 and K24. [8]. By substituting eqs.…”

“…Different microscopic models have been utilised in the literature to obtain the elastic constants [5,. In a recent paper, Barbero et al [8] used the Maier-Saupe model but they accounted for the anisotropy of the geometrical shape of the molecules (non-spherical molecules). If one makes the standard assumption of neglecting the geometrical anisotropy of the molecules (spherical molecules), this model predicts identical values for the splay, twist and bend bulk elastic constants Kll, K22 and K33 [5] in contrast with typical experimental results [6] that give Kll = K83 but K22 < Kll, K~8.…”

“…Far from the interface of the NLC sample, the elastic constants are independent of the position and of the orientation of director n. Close to the interface, due to the breaking of the translation symmetry, the elastic constants become functions of distance z from the interface and of angle 0 between the director and the unit vector k orthogonal to the interface [8,28]. Furthermore, new elastic contributions that are forbidden by symmetry in the bulk, become possible close to the interface.…”

“…The macroscopic consequence of these and other subsurface elastic anomalies has been extensively investigated in recent years [29][30][31][32][33][34][35]. [7,8,28]. In our opinion, the subsurface elastic anomalies can play a very important role on the macroscopic behaviour of NLCs.…”

“…In principle, the geometrical anisotropy of the molecules could be taken into account by using the Barbero et al [8] theoretical approach. This is a standard assumption that greatly simplifies the theoretical analysis.…”