Holographic polymer-dispersed liquid crystals using vinyloxytrimethylsilane

BACKGROUND: To reduce the driving voltage of transmission holographic polymer-dispersed liquid crystals (HPDLCs), the polymer interface was modified by incorporating various amounts of vinyloxytrimethylsilane (VOTMS) monomer to the conventional grating formulation based on polyurethane acrylate (PUA). RESULTS: With the addition of increasing amounts of VOTMS, the contact angle of the film and the droplet size of the liquid crystal (LC) monotonically increased, implying that the VOTMS segments of the polymer are preferentially exposed to the interfaces and provide greater immiscibility with LC molecules. The operating voltage monotonically decreased with increasing VOTMS content with a minimum switching voltage of about 15 V with a response time of about 10 ms. However, in the presence of VOTMS, the droplets coalesced and caused random scattering, thus lowering the off-state diffraction efficiency below that of virgin PUA. CONCLUSION: It was found that VOTMS was essential to drive the film. The VOTMS segments of the polymer are preferentially exposed to the polymer/LC interfaces and decrease the surface anchoring strength and also influence the orientation of LC droplets. Also, lower molecular weight bifunctional polypropylene glycol generally gave greater diffraction efficiency, confirming that grating formation is favoured with higher crosslink density due to the greater polymer/LC phase separation. (C) 2008 Society of Chemical Industry