Preparation and Characterization of Temperature-Triggered Microcapsules Fabricated via Low-Temperature Shear Method.

Emergency leakage repair in subway shield tunnels requires a technique to encapsulate highly reactive sodium silicate that is simple and field-deployable, yet no mature solution currently exists. The challenge lies in sodium silicate's strong alkalinity and high osmotic pressure, both of which corrode most shell materials. This study proposes a "composite core" concept-functionally re-engineering the core rather than relying on complex shell chemistries. Using hydroxypropyl methylcellulose (HPMC) as the key material, temperature-triggered microcapsules with a nano-silica shell and sodium silicate-HPMC core were fabricated via low-temperature shear. Low temperature (10-15 °C) is critical: it suppresses side reactions and tunes viscosity to 2000-5000 cP, facilitating shear dispersion. The resulting microcapsules exhibit well-defined morphology with a dense shell. Temperature response tests reveal distinct release onset at ~30 °C (HPMC's LCST): HPMC chain collapse generates internal stress that ruptures the shell, driving progressive sodium silicate release. Alkaline resistance tests confirm that intact microcapsules remain stable in high-pH environments (pH ≈ 13.2) for 30 min. This work validates the "composite core" concept and provides a simple, field-operable route to fabricate temperature-triggered microcapsules for emergency repair applications.