CF₄ plasma treatment of poly(dimethylsiloxane): Effect of fillers and its application to high-aspect-ratio UV embossing

Surface modification of poly(dimethylsiloxane) (PDMS) was carried out via CF₄ plasma treatment. The test PDMS used contains significant amounts of quartz and silica fillers, while the control material is the same PDMS with quartz removed by centrifugation. Fluorination accompanied with roughening was produced on both PDMS surfaces. With short plasma times (15 min or less), a macromolecular fluorocarbon layer was formed on the PDMS surfaces because of the dominant fluorination, leading to significant increase in F concentration, decrease of surface energy, and some roughening. With intermediate plasma times (15-30 min), dynamic balance between fluorination and ablation was achieved, leading to a plateau of the surface roughness, fluorine content, and [F-Si]/[F-C] ratio. At our longest investigated plasma time of 45 min, the plasma ablated the fluorinated covering layer on the PDMS surfaces, leading to significant increase in roughness and [F-Si]/[F-C] ratio and decrease of surface F concentration. The effect of additional quartz in the test PDMS on surface F concentration, [F-Si]/[F-C] ratio, and roughness was dramatic only when ablation was significant (i.e., 45 min). The obtained Teflon-like surface displays long-term stability as opposed to hydrophobic recovery of other plasma-treated PDMS surfaces to increase hydrophilicity. On the basis of the optimized plasma treatment time of 15 min, a microstructured PDMS mold was plasma treated and successfully used for multiple high-aspect-ratio (about 8) UV embossing of nonpolar polypropylene glycol diacrylate (PPGDA) resin.