Vapor-Phase Molecular Doping in Covalent Organosiloxane Network Thin Films Via a Lewis Acid-Base Interaction for Enhanced Mechanical Properties.

Incorporating inorganic components in organosiloxane polymer thin films for enhanced mechanical properties could enable better durability and longevity of functional coatings for a multitude of applications. However, molecularly dispersing the inorganic dopants while preserving the cyclosiloxane rings represents a challenge for cross-linked organosiloxane networks. Here, we report a molecular doping strategy using vapor-phase infiltration. On the basis of the proper Lewis acid-base interaction between diethyl zinc (DEZ) and cyclotrisiloxane rings, we achieved a complete infiltration of the organometallic precursors and well-distributed Zn-OH terminal groups formed in the initiated chemical vapor deposited poly(1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane) (PVD) films. X-ray photoelectron spectroscopy and nanoscale infrared spectroscopy together with density functional theory simulation reveal that the formation of a Lewis acid-base adduct rather than a ring-opening process is possibly involved in anchoring DEZ in the cross-linked network of PVD. Because of the incorporation of Zn-OH components, the organic-inorganic hybrid films obtained via our vapor-phase molecular doping exhibit a 10.2% larger elastic modulus and 67.0% higher hardness than the pristine PVD. Unveiling the reaction mechanisms between organometallic precursors and cross-linked organic networks provides new insights for expanding the vapor-phase processing strategies for engineering hybrid materials at the nanoscale.