Preparation of thermoswitchable chromic nanocapsules containing leuco-dye via miniemulsion polymerization

The study and improvement of organic thermochromic materials with reversible color changes have received a lot of attention during the recent years. In this work, miniemulsion polymerization was employed to encapsulate spirolactone-based leuco-dye with bisphenol A and tetradecanol (TDH) or dodecanol (DDH) into a crosslinked polymethyl methacrylate substrate. The optimized weight ratio of leuco-dye, bisphenol A, TDH or DDH and polymer substrate was estimated 1, 4, 70, and 75 g, respectively, to observe best thermochromic efficiencies. The prepared thermochromic nanocapsules containing TDH (TL@T) and DDH (TL@D) showed smooth, spherical shape with average particle size of 100 and 110 nm, respectively. The coated cellulose substrate with thermochromic nanocapsules showed switchable color changes from deep red to colorless by temperature variation from 0 to 25 °C for TL@D and 0 to 38 °C for TL@T. Encapsulation efficiencies of core materials for TL@D was 91.9% and 94.5%for TL@T. Reversible thermoswitching of the printed pattern with thermal resistance over 10 cycles of heating-cooling cycles approves the potent of these nanocapsules for temperature indicators and anticounterfeiting systems.