Electrically induced dynamic processes in nematic liquid crystals: H-1 nuclear magnetic resonance investigations

The director reorientation of some nematic liquid crystals in the presence of both magnetic and electric field is described by a modified from of the Leslie equation. Proton nuclear magnetic resonance experiments observing st atic director orientations in different angles between the director and the magnetic field are described together with reorientation experiments drive n by various electric fields. A new technique to measure Delta chi/Delta ep silon is presented which gives direct access to the anisotropies without an y influence of elastic properties. Using electric fields of different stren gth and in different angles with respect to the magnetic field the dynamic processes in liquid crystals can be investigated in a very flexible way. A number of experiments investigating the homogeneous director reorientation in the electric field is presented. As one result the rotational viscosity was determined. As a surprising result we found a homogeneous reorientation in the electric field and an inhomogeneous reorientation back in the magne tic field even though the initial angles between the director and the exter nal field were the same. (C) 2000 American Institute of Physics. [S0021-960 6(00)71130-5].