Manipulating the Surface Structure of Hybrid UV Curable Coatings through Photopolymerization-Induced Phase Separation: Influence of Inorganic Portion and Photoinitiator Content

Surface topography and phase-manipulated distribution of hybrid UV curable coatings is performed. Accordingly, phase separation is controlled by changing the inorganic/organic ratio and the photoinitiator content as these are the main thermodynamic and kinetic affecting factors, respectively. Chemical and mechanical evolution of the samples during photopolymerization is investigated by time-resolved Fourier transform infrared spectroscopy and photorheometry, respectively. It is found that the samples that contain larger portion of inorganic oligomers are polymerized faster, but undergo gelation later; this provides them more time to undergo phase separation prior to gelation. Therefore, their surfaces become rougher and more heterogeneous, which is confirmed by atomic force microscopey. Furthermore, adding larger amounts of photoinitiator into the samples leads to them being photopolymerized faster and undergo gelation at lower conversion. So, they have less time and thermodynamic tendency to undergo phase separation prior to gelation; their surfaces thus become smoother and more homogeneous.