Tailoring radicals at silica interfaces: a strategic approach for enhancing PTMA charge transfer in polymer matrix

Exploring a synthetic approach to control the radical density at inorganic particle interfaces, especially at silica particles, is challenging and needed to answer several ongoing research questions regarding charge transport efficiency and stability. Herein, we report our work on the grafting of different molecular weight poly[2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate] (PTMA) onto silica particles. Two distinct routes were explored for grafting TEMPO backbone monomer and polymers onto silica particles: first route involved direct functionalization under reflux conditions with a TEMPO monomer, while with second route, surface-initiated atom transfer radical polymerization (SI-ATRP) was employed to graft PTMA of varying molecular weights onto silica surfaces. The grafted silica particles are thoroughly characterized using IR, XPS, EPR, GPC, FESEM, TEM, and DLS techniques. Furthermore, these modified silica particles were utilized as additives to enhance charge transfer within the PTMA polymer matrix. To investigate the charge transport efficiency, different concentrations of modified silica particles are added to the different concentrations of PTMA in 0.5M lithium bis(trifluoromethane)sulfonimide (LiTFSI) in acetonitrile. This study elucidates the underlying mechanisms governing radical-silica surface interactions, providing valuable insights into optimizing charge transport phenomena at these interfaces. Leveraging the unique properties of PTMA and silica interfaces, our findings offer a pathway for the rational design of advanced materials tailored for high-performance electrochemical systems, particularly redox flow batteries.