Fig. 2
From: Optically-controlled long-term storage and release of thermal energy in phase-change materials
Experimental observation of phase change and heat storage in composites. a Photographs of composites of tridecanoic acid and 30 mol% of azobenzene dopants during solid-state heat absorption/ UV charging/cooling/visible-light-induced discharging and heat-release process. b UV-vis absorption spectra of the azobenzene dopant in dichloromethane solution, before and after UV illumination. The uncharged solution is saturated with trans isomers (dotted yellow line), showing peak absorption at 325 nm (π → π* transition), and the UV-charged solution saturated with cis isomers (solid red line) exhibits a n → π* transition peak at 440 nm48,49. c Differential scanning calorimetry (DSC) scans of charged and uncharged composites (35 mol% doped) obtained while cooling from 70 °C at a rate of 5 °C min−1, illustrating different crystallization points (T 1 and T 2) and the gap (ΔT c). Small peaks at 20 °C indicate the solidification of a minor polymorph50 in tridecanoic acid. d T 1, T 2 (left axis), and ΔT c (right axis) measured by DSC at a rate of 5 °C min−1 from composites with varying additive ratios. e Heat of fusion (i.e., crystallization enthalpy) measured by DSC at a rate of 5 °C min−1 and calculated on the composites with varying additive ratios. Error bars in d, e indicate standard deviations of the data (either temperature or heat of fusion) collected at least 5 times on each type of composite
