Double-shell microcapsules with enhanced thermal stability and low leakage for thermochromic and thermal energy storage textiles

In study, a novel type of thermochromic phase change system (TPCS) @polystyrene (PS) @silica (TPCS@PS@silica) double-shell microcapsule was designed by radical polymerization of styrene monomer and hydrolysis-condensation reaction of tetraethyl orthosilicate (TEOS). In the preparation of double-shell microcapsules, TPCS, composed of fluorane dye, bisphenol-A (BPA), and 1-tetradecanol (TD), was used as the core material. Polystyrene acted as the first organic shell to encapsulate the TPCS while silica acted as the second inorganic shell on the surface of the polystyrene shell. The aim of preparing double-shell microcapsules is to enhance the protection of TPCS, which are highly sensitive to environmental factors, and to improve the thermal stability and leakage resistance of the microcapsules. The thermal stability of the TPCS@PS@silica double-shell microcapsules was higher than that of the TPCS@PS single-shell microcapsules. Besides, the leakage rate of TPCS reduced from 4.1 to 1.8% after the addition of a second silica shell, compared to the use of a single polystyrene shell. TPCS@PS@silica double-shell microcapsules had an enthalpy of 123.6 J/g and exhibited a reversible color change from pink to white depending on temperature variation. The cotton fabrics treated with TPCS@PS@silica double-shell microcapsules using the bath exhaustion and pad-dry-cure processes not only showed thermochromic but also demonstrated thermoregulation performance. SEM images, photographs and colorimetric data showed that the fabrics treated by bath exhaustion process exhibited superior performance in terms of thermochromic and wash resistance compared to the pad-dry-cure process. The addition of microcapsules significantly reduced the air permeability of fabrics, but did not affect their bending resistance and tear strength.