Vapor-Phase Molecular Doping in Covalent Organosiloxane Network Thin Films Via a Lewis Acid–Base Interaction for Enhanced Mechanical Properties
Mingjun Qiu, Weiwei Du, Xinyu Luo, Siyuan Zhu, Yingwu Luo, Junjie Zhao
Abstract
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) (PV3D3) 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 PV3D3. 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 PV3D3. 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.