Phase equilibria and morphology development in liquid crystal/photo-curable monomer mixtures undergoing pattern photo-polymerization

Morphological development during pattern photo-polymerization of neat photo-curable multifunctional acrylate monomer was investigated theoretically by involving both modeling and simulation. Pattern photo-polymerization operates based on the interference of two or more laser beams coming in opposite directions to reflect at a certain angle on the sample, resulting in a spatial variation of intensity. A multi-wave interference instrument was constructed to facilitate pattern photo-polymerization. Optical microscopy (OM), atomic force microscopy (AFM), and two-dimensional light scattering (2D light scattering) were employed to characterize the photo-patterned samples. This study has been extended to monomer solutions with an isotropic solvent and to monomer/nematic liquid crystal mixtures.; To describe the physical essence of the systems above, various free energy forms were used such as the general Landau type of free energy, the Flory-Huggins (FH) free energy of isotropic mixing, and the Maier-Saupe (MS) free energy of nematic ordering. With chemical potential balance method, phase diagrams were established for monomer solution and monomer/liquid crystal mixtures. The spatio-temporal growth of structure was revealed by incorporation of the respective free energy or the combined free energy into the time-dependent Ginzburg Landau (TDGL) equations coupled with photo-polymerization kinetics.; The model parameters were determined experimentally to make the simulation more realistic. The FH interaction parameter was deduced from experimental establishment of phase diagram via cloud point measurement. The apparent reaction kinetic constant was obtained from photo differential scanning calorimetry (Photo-DSC) and Fourier transform infrared spectroscopy (FTIR) experiments. The numerical calculations show various morphologies observed experimentally. Various effects of liquid crystal content, beam intensity, and monomer functionality on the pattern formation have been demonstrated. Of particular significance was the prediction of diffraction efficiency progression, a key electro-optical property of patterned sample.