Electro-Optical Properties of Holographic PDLC Containing Polyhedral Oligomeric Silsesquioxane

Holographic polymer dispersed liquid crystal (HPDLC) was fabricated with different contents of polyhedral oligomeric silsesquioxane (POSS) at a specific polymer composition to optimize the electro-optical performance of the HPDLC film. The off-state diffraction efficiency increased gradually with the addition of POSS owing to the presumably increased elasticity of the polymer matrix and the immiscibility between the polymer matrix and the liquid crystal (LC). Phase separation of the polymer and the LC was augmented by effectively squeezing the LC molecules out of the polymer matrix. The effect of POSS on the diffraction efficiency was enhanced by increasing the added amounts of POSS. However, the diffraction efficiency decreased in the HPDLC film until above 5 % POSS because of fast polymerization and poor phase separation between the LC and the polymer. The HPDLC film containing POSS obtained a low driving voltage and a fast rising time due to a lowering of the anchoring energy at the polymer-LC interface, indicating that the POSS was preferentially exposed at the interfaces between the LC and the polymer due to the low surface energy of the silicon (Si) atom. A HPDLC film showing a low driving voltage (<50 V), a fast response time (<10 ms) and a high diffraction efficiency (>70 %) could be obtained with 3 wt% POSS at 40 wt% LC.