A bistable, polarizer-free, and reflective electro-optical switch based on a droplet manipulation on a liquid crystal and polymer composite film (LCPCF) is demonstrated. A color droplet on LCPCF can be manipulated by a wettability gradient owning to the distribution of LC directors anchored among the polymer grains on LCPCF. The contrast ratio is around 8:1 in a reflective mode. The potential applications of droplet manipulation are electronic papers and reflective displays.
An electrically switchable surface free energy on a liquid crystal and polymer composite film (LCPCF) resulting from the orientations of liquid crystal molecules is investigated. By modification of Cassie’s model and the measurement based on the Chibowski’s film pressure model (E. Chibowski, Adv. Colloid Interface Sci. 103, 149 (2003)), the surface free energy of LCPCF is electrically switchable from 36×10−3J/m2 to 51×10−3J/m2 while the average tilt angle of LC molecules changes from 0° to 32° with the applied pulsed voltage. The switchable surface free energy of LCPCF can help us to design biosensors and photonics devices, such as electro-optical switches, blood sensors, and sperm testers.
Developing a handy sperm testing device is important since sperm quality is a significant factor for fertility potential. In this paper, we demonstrate a sperm testing device based on a switchable surface, a liquid crystal and polymer composite film (LCPCF). The wettability of LCPCF is electrically switchable due to the electrically tunable orientations of liquid crystal molecules. In experiments, two motions of a semen drop on switchable surface of LCPCF are observed: back-and-forth stretches and collapses of semen drops. The better quality spermatozoa results in back-and-forth stretches of a semen drop on LCPCF; otherwise, the semen drop collapses. The motility and concentration of semen can also be sensed by the stretch distance and collapse distance of semen drops, respectively. The mechanism of back-and-forth stretches of semen drops results from fertile sperms swimming against the flow with the periodic changes of the orientation of LC molecules with pulsed voltages. The mechanism of collapses of semen drops results from the washed-away infertile sperms which are deposited on LCPCF and then re-modify surface of LCPCF. Potential applications for this device include sperm testers and microfluidic devices for Assisted Reproductive Technology.
This study demonstrates the electrical control of the surface wettability of liquid crystal and polymer composite film. The application of external voltages significantly affects the surface wettability of the film. This study uses atomic force microscopy to quantitatively characterize the fundamental mechanism responsible for the structurally driven changes in surface properties at various applied voltages. The surface wettability transitions of the film are electrically driven, as shown by reorganized liquid crystal molecules. Measurements of the voltage-dependent surface wettability of the composite film suggest approaches to supporting control applications of future electro-optical nanotechnology devices.
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