Thermochromic composite material, its preparation and use

A composite material for use in a window unit comprising:

• a substrate body having a mesoporous structure of delignified wood defined by a network of interconnected fibers;
• and
• a thermochromic material comprising a hydrogel complex filling and being supported by the mesoporous structure, the hydrogel complex comprising a refractive index-matching polymer including poly(acrylamide) (PAM), the refractive index-matching polymer forming a first crosslinked network holding a plurality of microgel particles of a thermoresponsive hydrogel including poly(N-isopropylacrylamide) (PNIPAM);
• wherein the plurality of microgel particles of the thermoresponsive hydrogel undergo a phase transition in direct response to an external temperature exceeding or falling below a critical transition temperature of the thermochromic material, thereby changing an overall transparency of the composite material;
• and
• wherein the critical transition temperature (Tc) of the thermochromic material is from about 20° C. to about 25° C.