Preparation and characterization of the thermochromic microcapsules and temperature-indicating hydrogel

Thermochromic composites were prepared by using thermal dye CK-16 as color former, bisphenol-A as a color developer, and the mixture of tetradecanol with hexadecanol as co-solvent. The ratio of raw materials was optimized. The effect of each ingredient on the melting point of the composite was investigated by differential scanning calorimetry (DSC). With the thermochromic composite as core material and with an urea-formaldehyde condensate as wall material, the thermochromic microcapsules were fabricated through in-situ polymerization. The particle size and external morphology of thermochromic microcapsules were characterized by scanning electron microscopy and laser particle size analyzer. The thermal stability of the microcapsules was studied by thermal gravimetric analysis. The preparation conditions of the microcapsules were optimized. An obvious color change of the microcapsules was observed at about 40 degrees C. The hydrogels were produced by the physically cross-linking method with polyacrylic acid sodium, sodium alginate, and the thermal dye microcapsules as raw materials. The hydrogels were characterized by DSC, rheometer, and infrared spectrum, and the optimum ratio of the ingredients in the hydrogel was determined. The hydrogels were applied to a cooling gel sheet with temperature indication.