A dedicated protocol to capture orthosilicate crosslinking kinetics and Arrhenius parameters

Abstract

Organosilica sol–gel synthesis is an important chemical process to deliver advanced functional network materials with applications such as wound dressings, solar cells and membranes. The chemical kinetics are although poorly understood, due to a lack of Arrhenius parameters and a focus on kinetic data mainly recorded at 298 K. The present work overcomes these shortcomings by reporting Arrhenius parameters for the most important reactions (hydrolysis and condensation), selecting tetraethyl orthosilicate (TEOS) crosslinking with hydrochloric acid (HCl) as reference case. A dedicated 29Si nuclear magnetic resonance (NMR) protocol applicable at any process temperature, with better relaxation delay optimization, peak identification, and an automated correction for further reaction during analysis at 298 K, is put forward. NMR is the analysis technique of choice to quantitatively follow the reactions in time due to its high specificity. This novel NMR-based protocol enables a more reliable quantification of the contribution of species that have been crosslinked i times (Q1-Q4). The tuned Arrhenius parameters, employing coupled matrix-based Monte Carlo simulations, can describe the isothermal kinetics for temperatures ranging from 298 to 328 K well. Moreover, these Arrhenius parameters are used to better understand the non-isothermal kinetics as utilized to synthesize sol/gel-like precursor solutions for applications including membrane production. Successful model validation under both isothermal and non-isothermal conditions is demonstrated, unlocking the door to a better understanding of orthosilicate crosslinking kinetics and associated material properties.