Direct Observation of Liquid Crystal Droplet Configurational Transitions using Optical Tweezers

Liquid crystals (LCs) are easily influenced by external interactions, particularly at interfaces. When rod-like LC molecules are confined to spherical droplets, they experience a competition between interfacial tension and elastic deformations. The configuration of LCs inside a droplet can be controlled using surfactants that influence the interfacial orientation of the LC molecules in the oil-phase of an oil in water emulsion. Here, we used the surfactant sodium dodecyl sulfate (SDS) to manipulate the orientation of 5CB molecules in a polydisperse emulsion and examined the configuration of the droplets as a function of SDS concentration. We triggered pronounced morphological transitions by altering the SDS concentration while observing an individual LC droplet held in place using an optical tweezer. We compared the experimental configuration changes to predictions from simulations. We observed a hysteresis in the SDS concentration that induced the morphological transition from radial to bipolar and back as well as a fluctuations in the configuration during the transition.

Clinical applications of the Matching Familiar Figures Test: impulsivity vs. unilateral neglect

Impulsivity is a common consequence of brain damage, one with negative prognostic implications. To attempt to study the incidence of impulsivity after lateralized cerebral lesions, 93 patients (50 RBD, 43 LBD) and 24 normal controls were administered the Matching Familiar Figures Test, a visual match-to-sample task in a multiple-choice format. The groups differed significantly (RBD less than LBD less than Controls) with respect to accuracy (visual-perceptual skill). Average response latency scores of the brain-damaged groups were slightly, but not significantly, lower than that of Controls. Although more than one-third of the RBD showed a tendency to respond rapidly, reduced response latency in RBD patients may be due, not to impulsivity per se, but, rather, to incomplete visual scanning characteristic of neglect. The present results illustrate the hazards of interpreting neuro-psychological test scores without consideration of pertinent processing variables.