Dynamic behavior of photo-induced orientation of poly(methyl methacrylate) – Solvent Red 23 thin films

We investigate the effect of the photo-orientation and stability of the Solvent Red 23 dye incorporated in poly(methyl methacrylate) thin films as a guest–host system. A probe–pump optical system was used to investigate the dichroic behavior of the samples. Orthogonally polarized laser lights induce a smaller increase in the transmitted beam intensity. A stronger polar order was induced using a parallel probe–pump laser light compared to that of the perpendicular state. It was found that the dichroic ratio value of the poly(methyl methacrylate) – Solvent Red 23 thin film increased by 0.174 at the photostationary state, indicating that the net orientation of Solvent Red 23 molecules has increased 17.4% in the direction perpendicular to the applied beam field. The dynamic evolution of the dichroic ratio showed that the relaxation is rather slow, and it deteriorates in a slow exponential fashion, which may take a very long time to reach the isotropic state. The contrast ratios were 0.449 and 0.267 in parallel and orthogonal probe–pump configurations, respectively. The order parameter calculations reveal that about 70% of photo-induced anisotropy remains after relaxation for a long time.

Molecular Orientation Study of the Drying of Latex in Real Time Using the Variable-Angle Attenuated Total Reflectance Technique

The changes in orientation of polymer chains during the drying of latex have been studied. The Fourier transform infrared spectroscopy-attenuated total reflectance (FT-IR ATR) technique was used to obtain dichroic ratios. The variable-angle ATR technique was used to profile the dichroic ratio changes at different depths in the films. Using the dichroic ratio and the Hermans orientation function, it was possible to monitor the orientation changes of the polymer chains during latex drying in real time. New insights into the film formation process during the different stages of drying and condensation were obtained.