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

Area of Science:

• Materials Science
• Chemical Engineering
• Civil Engineering

Background:

• Emergency repair of subway shield tunnels faces challenges with reactive materials like sodium silicate.
• Existing methods lack field-deployability and struggle with sodium silicate's corrosive properties.

Purpose of the Study:

• To develop a simple, field-deployable encapsulation technique for sodium silicate.
• To address the limitations of current repair materials in subway tunnel applications.

Main Methods:

• Fabrication of temperature-triggered microcapsules with a nano-silica shell and sodium silicate-hydroxypropyl methylcellulose (HPMC) core using low-temperature shear.
• Utilizing HPMC's Lower Critical Solution Temperature (LCST) for triggered release.
• Testing alkaline resistance and temperature-dependent release characteristics.

Main Results:

• Successfully fabricated microcapsules with a dense nano-silica shell and a sodium silicate-HPMC core.
• Demonstrated triggered release of sodium silicate at approximately 30 °C due to HPMC chain collapse.
• Confirmed microcapsule stability in high-pH environments (pH ≈ 13.2) for 30 minutes.

Conclusions:

• Validated the "composite core" concept for encapsulating reactive materials.
• Provided a simple, field-operable method for fabricating temperature-triggered microcapsules.
• The developed microcapsules show promise for emergency subway tunnel repair applications.