Effect of gel-point versus conversion on the real-time dynamics of holographic polymer-dispersed liquid crystal (HPDLC) formation

We present data that indicates much more uniform reflection grating notches are formed when using thiol-ene photopolymerization as compared to the typical multifunctional acrylate photopolymerization. The scaling behavior of both diffraction efficiency and notch bandwidth versus thickness is presented for both acrylate and thiol-ene-based polymer hosts. The latter follows predicted behavior over a much larger range of thickness than the former. We attribute these differences to a delay in the gel-point with respect to the reaction start. Since the bulk of shrinkage occurs before gelation, detrimental effects caused by anisotropic stress build-up and subsequent relaxation is minimized. Using real-time monitoring techniques, we monitor the blue shift of the notch wavelength and the bandwidth development as a function of time for both chemistries. We demonstrate that thicker samples with appreciable diffraction efficiency and narrow bandwidths can be obtained.