Measurement of the surface-induced order in polymer dispersed liquid crystals: an approach by NMR relaxometry

A method based on NMR relaxometry is introduced to study surface-induced order in the isotropic phase of confined liquid crystals. We show that the magnitude of the surface order parameter S0 can be obtained from an increase in the deuteron transverse relaxation rate T-12. The increase originates in the molecular diffusion between the weakly ordered surface region and disordered area in the rest of the cavity. No assumptions concerning the residence time of molecules at the surface are needed. We apply the approach to a polymer dispersed liquid crystal and find a temperature independent S0 of magnitude congruent with 0.08. This indicates that short range interactions at the interface dominate the behavior of S0, and that only a partial orientational wetting occurs.