(167x) Reaction-Diffusion-Controlled Photopolymerization in Topographical Structures

There has been extensive research on oxygen inhibited photopolymerization, a phenomenon that the surface of a polymer exposed to the atmosphere “unpolymerize” due to scavenging free radicals by oxygen molecules. Due to this inhibition, polymer surface layer of few microns remains tacky. Most of the previous studies are investigated in one-dimensional analysis about oxygen diffusion and polymerization in film. However, this analysis can address only flat surface and cannot explain unexpected phenomena arise in higher dimensions, such as the curvature of the polymerized surface, which arises when the thickness difference in polymer exists.

This presentation deals with oxygen inhibition of UV-curable polymers placed on micron scales topological structures/templates which are widely used in soft lithography. The effects of the template geometry and the thickness of the coated polymer, as well as initiation rate, which influence the reaction are investigated. To this end, two-dimensional finite element modeling was applied and compared with experimental results. Through the oxygen concentration gradient in template which results the variance of polymer thickness, it was confirmed that not only the template plane-parallel polymer shape but also the non-flat, pseudo-3D one could be made. Furthermore, this oxygen concentration gradient accounts for low fidelity polymerization on PDMS templates, well known for its high oxygen permeability. By using this analysis, this presentation is for giving new insights for delicate control over polymer surface, which is fabricated by topological templates.