Investigation of New Cooling Paints Based on Copolymers of N-Isopropylacrylamide with Butyl Acrylate and N,N-Dimethylacrylamide

New cooling paints were developed by exploiting the vaporization heat of water. These systems were prepared using various ratios of three copolymer components N-isopropylacrylamide (NIPAAm), butyl acrylate (BA), and N,N-dimethylacrylamide (DMAAm). The homopolymer of NIPAAm dissolves in water below about 32°C (hydrophilic) and becomes insoluble above this temperature (hydrophobic). On the basis of the hydrophobic/hydrophilic switch of NIPAAm polymers, cooling paints consisting of copolymers of NIPAAm with coating materials were investigated. Copolymers of NIPAAm with BA (NIPAAm-co-BA) showed cooling effects; however, the hydrophobic/hydrophilic switch temperature decreased with the BA ratio. Copolymerization of NIPAAm-co-BA and DMAAm allowed us to adjust the switch temperature to about 30°C. In addition, when the copolymers were pasted on the wall of a model house, at night (temperatures below approximately 30°C), water molecules from the air were adsorbed on the materials, and when the outside temperature increased, the temperature of the room decreased. These new coating materials could cool the room on hot days without the need for electrical energy or labor.