Design and evaluation of a thermochromic roof system for energy saving based on poly(N-isopropylacrylamide) aqueous solution

A novel thermochromic system for energy saving purpose was designed through employing aqueous solution of poly(N-isopropylacrylamide) (PNIPAM), a thermosensitive polymer. The system consisted of a glass cell filled with aqueous solution of PNIPAM. The cell bottom was covered by black fabric. At low temperature, the solution was transparent giving the cell black color that absorbed light. When the temperature was raised to above the lower critical solution temperature (LCST) of PNIPAM, the solution became opaque. As a result the cell appeared white and reflected the light. The reflection ratio was determined by the concentration of aqueous solution of PNIPAM. When the concentration of PNIPAM reached 0.05g/mL, a maximum reflection ratio of 33% was observed which led to a decrease of the cell temperature by 6.0°C compared with the cell without PNIPAM inside.