Dependence of viscoelastic parameters of nematic liquid crystals on pretilt angle and temperature

The viscoelastic parameters of nematic liquid crystal (LC) E7 in both splay and twist relaxation modes are investigated as functions of pretilt angle and temperature by the technique of dynamic laser light scattering. The results show that the elastic constants of the liquid crystal in the two modes not only depend on temperature, but also depend on pretilt angle. There is a critical pretilt angle (βC) at which nematic LC begins exhibiting elastic property, and beyond which the elastic constants increase with pretilt angle, then keep constant after exceeding another angle (βS, with βS > βC). This phenomenon is observed to be universal for different nematic LC's, and significant not only in the understanding of the molecular mechanism of exhibiting viscoelastic properties in nematic LC, but also for their practical purpose.