Investigation of Structure and Dynamics in the Fibre-Type Nematic Phase of nBABA

Abstract

Neutron diffraction measurements have been carried out with chain deuterated (D-) and non-deuterated (H-) compounds, p-n-AlkoxyBenzylidene-p-Amino Benzoic Acids (nBABA, n = 1, 3, 4 and 7) in the fibre-type nematic (N _F) phase. For n = 3 and 4, our results indicate the presence of strings of one dimensional (1-d) correlated molecules parallel to ň, the nematic director. The number of strings as well as the correlation length, ξ¹ _⊥, perpendicular to ň, decrease rapidly with increasing temperature. However, ξ¹ _‖, the correlation length parallel to ň, remains almost constant for T _PN ≤ T < T _PN + 30°C (T _PN = crystal to nematic transition temperature), but decreases for larger T. Neutron quasi-elastic scattering experiments carried out with 4BABA (both D- and H-) in the N_F phase have shown that, (a) the rotational diffusion times, τ ^r ₁ and τ ^f ₁, for the rigid and flexible parts of the molecule, are not very different, and are ∼10⁻¹¹s for T ≈ T_PN , and (b) these motions are not influenced greatly by the 1-d correlation of the molecules.