Transient phenomena of relaxation from electric‐field‐induced nematic phase to cholesteric phase

摘要

In certain mixtures of nematic and cholesteric liquid crystals, it is found that the metastable final state in an electric‐field‐induced nematic to cholesteric transition depends on the turnoff rate of the applied voltage. Experimental evidence sugests that two processes, i.e., helix winding and Freedericksz transition type molecular reorientation, may be involved. Relaxation times for both are estimated theoretically and compared with experimental results. An overall relaxation process is also proposed phenomenologically and the predictions compare favorably with the temporal data. The prerequisites on the threshold fields and relaxation times for this phenomenon are deduced. It is believed that this new observation may help explain the transient behavior in a nematic‐cholesteric phase transition and may promise some practical applications.