Elucidating Photochemical Conversion Mechanism of PDMS to Silica under Deep UV Light and Ozone

Abstract

Photochemistry-based silica formation offers a pathway toward energy-efficient and controlled fabrication processes. While the transformation of poly(dimethylsiloxane) (PDMS) to silica (often referred to as SiO_x due to incomplete conversion) under deep ultraviolet (DUV) irradiation in the presence of oxygen/ozone has experimentally been validated, the detailed mechanism remains elusive. This study demonstrates the underlying molecular-level mechanism of PDMS-to-silica conversion using density functional theory (DFT) calculations. Our findings reveal that atomic oxygen plays a key role in converting PDMS to silica by catalyzing the replacement of -CH₃ groups to -OH groups, with a barrier-less insertion into Si–C and C–H bonds, eventually leading to condensation reactions that produce silica and formaldehyde and/or formic acid as byproducts. The proposed molecular pathway has further been validated through controlled experiments, which confirm the successive -CH₃ to -OH replacements and identify gaseous byproducts such as formaldehyde. These findings offer insights into the fundamental processes involved in photochemistry-based silica fabrication and could pave the way for advancements in energy-efficient materials synthesis.