Curing Dynamics of Photopolymers Measured by Single-shot Heterodyne Transient Grating Method

Abstract

The heterodyne transient grating (HD-TG) method was first applied to the curing dynamics measurement of photopolymers. The curing dynamics for various monomers including an initiator (2.5 vol%) was monitored optically via the refractive index change after a single UV pulse irradiation. We could obtain the polymerization time and the final change in the refractive index, and the parameters were correlated with the viscosity, molecular structure, and reaction sites. As the polymerization time was longer, the final refractive change was larger, and the polymerization time was explained in terms of the monomer properties.

Molecular dynamics in azobenzene liquid crystal polymer films measured by time-resolved techniques

“…Furthermore, the time region for this component is a typical thermal response time for polymers or thin films. 26,27 It is reasonable that this component was caused by the density change due to temperature increase, which was lost when the film thickness was decreased, because a thinner layer caused a smaller phase change for the probe light, which is the origin of the HD-TG signal. The thermal diffusion time did not depend on the temperature so much, which indicates that the thermal conductivity of the film was similar for both temperatures, but it looks slightly faster for a probe polarization parallel to the molecular orientation than for a probe polarization perpendicular to the molecular orientation, which indicates the anisotropic thermal property of the film.…”

“…The disordered alignment of the LC returned back to its original state in a LC cell. [23][24][25] Since this technique detects changes in the refractive index, it is suitable to observe soft materials such as polymers or LCs, 24,26 which typically do not have optical absorption in the visible wavelength region. The change in the refractive index typically reflects the order parameter for LC samples, from which we can get information on the molecular rotation and the ordering state of the LC molecules in the temporal domain.…”

Depth-selective microscopic observation of a photomobile liquid crystal polymer under UV illumination

“…11,12 Since the refractive index change was detected in this method, it is suitable for LC or polymer samples because they typically have no optical absorption bands in the visible wavelength region. 13,14 We could observe the initial film contraction on the order of several hundreds of nanoseconds, the subsequent reorientation and molecular rotation dynamics from a few microseconds to a hundred milliseconds, and the return of the cis isomer to the trans isomer on tens of seconds. Furthermore, we figured out that the molecular orientation by the UV irradiation was highly anisotropic under the conditions preferred for the mobility.…”