Turn-on Times for Torsional Straining of a Lyotropic Nematic in a Magnetic Field with an Arbitrary Orientation Relative to the Director

The dynamics of torsional straining of a lyotropic nematic with a negative diamagnetic susceptibility anisotropy in the disulfoindantrone dye–water system in a magnetic field with an arbitrary orientation relative to the director is investigated. The turn-on times of the torsional straining are determined experimentally as functions of the squared magnetic field strength for four different values of the angle between the director and the magnetic field. It is shown that with increasing square of the magnetic field strength (at a fixed angle), the turn-on time decreases, while with increasing angle (at a fixed magnetic field strength), the turn-on time increases; the torsion turn-on time is of the threshold nature. The behavior of the turn-on time depending on the square of the magnetic field strength is described by an approximating function, the form of which has been obtained earlier from analysis of stability for the director motion equation describing the torsional deformation.