Real-time generation of dynamically patterned cholesteric liquid crystal fingerprint textures based on photoconductive effect.

We present a convenient approach to facilitate the real-time generation of updatable dynamically patterned cholesteric liquid crystal (CLC) fingerprint textures based on photoconductive effect. The photoconductive Bi12SiO20 (BSO) substrate acts as virtual electrode to obtain the desired states of CLCs by both electric and light fields. Owing to different boundary conditions, the switching of four states; that is, planar, fingerprint, metastable, and homeotropic states, and the rotation of fingerprint stripes can be achieved in planar alignment (PA) cell and hybrid alignment (HA) cell, respectively. With the aid of a digital micro-mirror (DMD)-based exposure system, binary and gray-scale images were successfully written and updated by light upon suitable voltages. This work provides an alternative approach to photoaddress CLC fingerprint patterns, without needing special photoalignment agents or photoresponsitive chiral dopants. We expect that it could be employed in the manipulation of nano/micro-objects by light.

Photoalignment of dye-doped cholesteric liquid crystals for electrically tunable patterns with fingerprint textures.

We present a convenient photoalignment approach to fabricate rewritable fingerprint textures with designed geometrical patterns based on methyl red doped cholesteric liquid crystals (MDCLCs). MDCLC systems with/without nanoparticles of polyhedral oligomeric silsesquioxanes (POSS) were employed to realize two types of sophisticated binary patterns, respectively. Based on the understanding of involved mechanisms related to boundary conditions and middle-layer theory, we demonstrated the precise manipulation of fingerprint patterns by varying the fingerprint grating vectors in different domains. Notably, the hybrid-aligned liquid crystal configuration induced by POSS nanoparticles, which leads to the electrically rotatable grating, can be converted into the planar-aligned configuration by the adsorption of photoexcited methyl red molecules onto the indium-tin-oxide (ITO) surface. In this manner, the dynamic voltage-dependent behavior of fingerprint gratings is altered from the rotation mode (R-mode) to the on-off mode (O-mode).