New focus of the cloud point/Krafft point of nonionic/cationic surfactants as thermochromic materials for smart windows.

A nonionic poly(oxyethylene) monoalkyl ether (C 12 (EO) 6 ) and a cationic hexadecylpyridinium bromide (HPB) were used to achieve warm/cool transparency transition switchability, depending on the decrease in the hydration of the EO-headgroup of C 12 (EO) 6 above the cloud point ( T c ) and the crystallization of HPB below the Krafft point ( T k ). The liquid state shows the advantage of being free-flowing, frost-resistance, flexible-adjustment and solar-energy-storing-capability due to the moisture-rich characteristics, while the hydrogel state exhibits free-standing properties.