[Reaction kinetics investigation of NVP in HPDLC gratings]

In order to get the HPDLC grating with high diffraction efficiency and perfect surface morphology, NVP was added into the reaction system of fabricating gratings and then the influence of NVP on the reaction kinetics of HPDLC was described. The analysis showed that NVP significantly increased the rate of polymerization in HPDLC photopolymerization, and as the highly cross-linked polymer network forms, the small mono-vinyl NVP appeared to react preferentially with double bonds inthe reaction system, facilitating additional conversion of pendant double bonds otherwise trapped in the polymer network. Furthermore, NVP also enhanced the degree of phase separation and got perfect surface morphology as well as higher refractive index modulation. So, the diffraction efficiency of HPDLC gratings was remarkably improved. However, the surface morphology and diffraction efficiency of HPDLC gratings would be worse when the concentration of NVP was too high. In a word, the addition of NVP could significantly increase the polymerization rate and reaction extent of reaction monomer and ultimately get the HPDLC grating with high diffraction efficiency (96.36%) and perfect surface morphology.