Magnetic and electric field induced bistability in nematics and cholesterics

Magnetic field induced bistability in nematics and cholesterics: general deformations

“…However, the deformations for the two values of a are somewhat different. It can be seen (see, for instance, figure 1 of [14]) that…”

“…The boundary conditions for n and v become Let us first consider a nematic ( k , = 0). The same procedure adopted in [14] can also be used here to put equations It can be seen that for given material and boundary conditions, the only free parameter is R. If R is also fixed, equation (4.6) will yield solutions @(& u) and @(& u) which will be independent of sample thickness. It must be noted that z depends on h.…”

“…We can think of a situation where a (or 8) is a constant and fi= R,t (or c1 =Rat); starting from t = 0, H from equation (2.2) is rotated at a constant uniform rate. From an experimental viewpoint this would be a generalization of the rotating field experiment discussed in [14]. As long as R, or R, is small enough, equations (4.1) and (4.2) may be able to describe the way the distortion changes in time.…”

“…While this approach cannot yield the actual transition time between the states it can still establish that an instability might set in. This has been accomplished in the simple case of twist geometry [14] where flow coupling does not exist in the framework of the assumptions made. It should be interesting to find out whether similar results can be obtained when coupling between orientation and flow fluctuations cannot be neglected.…”

“…In the simple one angle description a numerical solution of the problem has been presented [13] by ignoring flow coupling; interestingly, this agrees well with experimental observations. An alternative approach [14] is to study the stability of the static solution against time dependent perturbations and to find out whether the perturbations have a tendency to grow near the edges of the bistable region. While this approach cannot yield the actual transition time between the states it can still establish that an instability might set in.…”