Mesoporous Silica-Pnipam Hybrid Microcapsules with Thermally Gated Pore Networks for Controlled Release of Waste Soybean Oil in Bitumen Rejuvenation

The development of mesoporous hybrid materials with stimuli-responsive pore networks offers a promising platform for controlled release applications. In this study, we synthesize mesoporous silica microcapsules functionalized with poly(N-isopropylacrylamide) (PNIPAM) as thermally gated molecular valves for the controlled delivery of waste soybean cooking oil (WSCO) to rejuvenate aged bitumen. Using an oil-in-water emulsion and sol–gel polymerization, we produce microcapsules with a well-defined core–shell architecture, featuring a WSCO core and a mesoporous silica shell with pore sizes of 10 to 30 nm and a thickness of 100 to 300 nm. PNIPAM is incorporated within the mesopore network via hydrogen bonding between its amide groups and surface silanols, forming spatially distributed polymer domains that act as reversible gates. Below the lower critical solution temperature (LCST) of approximately 32 °C, the hydrated PNIPAM chains expand to block the mesopores, restricting WSCO diffusion. Above the LCST, chain collapse opens the pore networks, enabling rapid release. Franz diffusion cell measurements reveal a temperature-dependent release profile, with 85