Phase Segregation of Polymethylsilsesquioxane in Antireflection Coatings

Abstract

We herein describe the preparation and characterization of a phase-separated fluorinated polymethylsilsesquioxane (PMSQ), which may be used as an antireflective coating. The results of FTIR analysis showed that when PMSQ is synthesized from methyltrimethoxysilane (MTMS), it exists mostly in the form of a cage structure. Its reflectivity of normally incident light ( R ) may be reduced from 3.9 to 0.9% by grafting 1 H,1 H,2 H,2 H -perfluorooctyltriethoxysilane (FTES) by means of a sol–gel process. In the study described herein, the minimum reflectivity of PMSQ was lowered to less than 1% by coating it with a single layer of fluorinated polymethylsilsesquioxane, through phase segregation of PMSQ and FTES that took place during film formation. The RI of PMSQ at 550 nm was also reduced from 1.51 to 1.42 by heating at 80 °C for 30 min, a temperature suitable for substrates, such as plastics, that have low heat resistance. Wetting and adhesion to substrates were both improved by the additional grafting of tetraethoxysilane (TEOS), again by means of a sol–gel process. Results of solid-state 29 Si NMR and GPC showed increases in T 3, Q 3, Q 4, and the molecular weight, which signal the effective grafting of both the TEOS and the FTES on the PMSQ. Results from energy-dispersive X-ray spectroscopy (EDX) show that the quantity of fluorine atoms at the surface of the PMSQ film increased from 0 to 22%, providing the evidence of the phase segregation within the PMSQ film. When FTES is used, we found an increase in the water contact angle from 92° to 108°, which indicated that the hydrophobicity at the PMSQ film surface increased by increasing the FTES content from 0 to 100 wt %, using the weight of MTMS as 100%.