Passive thermally driven variable opacity materials

A variable opacity material comprising an emulsion of an aqueous polymeric solution and a hydrophobic polymer, wherein:

• the aqueous polymeric solution comprises hydroxypropyl cellulose or poly(N-isopropylacrylamide) and from 10 to 60 wt. % of an alkaline earth metal salt, wherein the hydroxypropyl cellulose or poly(N-isopropylacrylamide) phase separates at temperatures above the lower critical solution temperature (LCST),
• the aqueous polymeric solution has an LCST from 0 to 100° C.,
• the aqueous polymeric solution is emulsified in the hydrophobic polymer,
• the aqueous polymeric solution is a discontinuous phase of the emulsion and the hydrophobic polymer is a continuous phase of the emulsion, and
• below the LCST, the difference between refractive indices of the aqueous polymeric solution and the hydrophobic polymer is less than or equal to 0.05.