As a Summer Research Assistant at the Liquid Crystal Institute (LCI) in Kent, Ohio, Stephen investigated the bistability of a smectic-A liquid crystal called 4’-octyl-4-biphenylcarbonitrile (8CB). 8CB is stable when switched between transparent (light transmitting) and opaque (light scattering) states. Unfortunately, 8CB will not switch in its most pure form. Stephen successfully doped multiple samples using different concentrations of an ion-pair reagent called tetrabutylammonium iodide. The presence of this organic salt in the liquid crystal allows the parallel layers to become unaligned, scattering light in all directions. The correct concentration of ions must be used in order for 8CB to remain bistable and still be in the smectic-A phase. This critical concentration was found by measuring the capacitance and resistance of multiple samples.
"Calculating the velocity of ions in my samples also proved to be very interesting. Finally, using a helium laser, photo-sensor, and digital phosphor oscilloscope, I measured the switching time between opaque and transparent states. This allowed me to further optimize my liquid crystal cell and experiment with different frequency and voltage settings."
Watch the actual movies of Stephen's experiment