通过优化分子结构实现相变偶氮苯的可控热释放用于低温能量利用

Controllable heat release of phase-change azobenzenes by optimizing molecular structures for low-temperature energy utilization

相变偶氮苯衍生物可以基于异构化储存和释放热量.热量输出量和速率受偶氮苯结晶和异构化的影响,同时也受分子结构和相互作用的制约.因此,优化分子结构是控制不同温度下热量释放的一种有效方式.在此,我们制备了三个不对称的烷氧基取代的偶氮苯分子(sAzo),其分子量相似但取代基不同,以研究结晶和异构化之间的权衡.我们研究了s-Azo的温控结晶性和光诱导的异构化动力学.结果表明,由于较强的范德华力,正烷氧基取代使s-Azo具有较高的结晶焓(ΔHCE),但立体阻碍降低了异构化程度.短烷基支化降低了分子相互作用,有利于异构化,使异构化焓(ΔHIE)增加,但降低了ΔHCE.正烷氧基取代的sAzo在-60.49至34.76℃的宽温度范围内表现出光诱导的高能热释放,焓值高达343.3 J g^(-1),功率密度为413 W kg^(-1).同步放热使分布式能量利用的环形装置在低温环境(-5℃)下实现了6.3℃的温升.结果表明,相变偶氮苯衍生物可以通过优化分子结构和相互作用应用于理想的储能系统.

Phase-change azobenzene derivatives can store and release heat upon isomerization.The amount and rate of heat output are affected by the azobenzene crystallization and isomerization,which are in turn governed by molecular structure and interactions.Thus,optimizing molecular structure is a promising method to control heat release at different temperatures.Herein,we prepared three asymmetric alkoxy-substituted azobenzene molecules(s-Azo)with similar molecular weights but different substituents to investigate the trade-off between crystallization and isomerization.Temperature-dependent crystallizability and photo-induced isomerization kinetics of all s-Azo were studied.Results indicate that n-alkoxy substitution endows s-Azo with high crystallization enthalpy(ΔHCE)due to strong van der Waals forces,but steric hindrance lowers the degree of isomerization.Short branched alkyl substitution reduces intermolecular interactions and favors the isomerization,which leads to an increase in isomerization enthalpy(ΔHIE)but decreasesΔHCE.The nalkoxy-substituted s-Azo exhibits photoinduced high-energy heat release with an enthalpy of up to 343.3 J g^(−1) and a power density of 413 W kg^(−1) at a wide temperature range from−60.49 to 34.76℃.The synchronous heat release in a distributed energy utilization annular device achieves a temperature rise of 6.3℃ at a low temperature environment(−5℃).Results demonstrate that phase-change azobenzene derivatives can be designed and developed for ideal energystorage systems by optimizing molecular structures and interactions.