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Strong, thermo-reversible salogels with boronate ester bonds as thermal energy storage materials
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2022-09-22 , DOI: 10.1039/d2ta06183j Kartik Kumar Rajagopalan 1 , Xiuzhu Zhu 1 , Svetlana A. Sukhishvili 1
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2022-09-22 , DOI: 10.1039/d2ta06183j Kartik Kumar Rajagopalan 1 , Xiuzhu Zhu 1 , Svetlana A. Sukhishvili 1
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Inorganic salt hydrates are promising phase change materials (PCMs) but suffer from low viscosity at temperatures above their melting point resulting in leakage problems during thermal storage applications. To achieve shape stabilization of one type of molten inorganic PCM – calcium nitrate tetrahydrate (CNH) – this work explored gelation of polyvinyl alcohol (PVA) in this solvent and the effect of dynamic boronate ester bonds on salogel strength. The occurrence of gelation of PVA in molten CNH but not in water is rationalized by the extremely high salt content and scarcity of hydration water in CNH, enabling intermolecular hydrogen bonding between PVA chains. While neat PVA salogels in CNH were weak, with a gel-to-sol transition temperature (Tgel) below room temperature, the addition of small amounts of borax (<∼0.3 wt%) introduced dynamic covalent crosslinks and yielded salogels with Tgel tunable over a wide temperature range from 7 to 70 °C. The PVA/borax salogels were about one order of magnitude stronger than their well-known PVA/borax hydrogel counterparts, and, unlike PVA/borax hydrogels, were capable of retaining their shape and preventing leakage of molten CNH. Moreover, the salogels exhibited reversible and repeatable temperature-triggered gel-to-sol transitions and the ability to self-heal. The low polymer and crosslinker concentration also ensured that more than 95% of the heat of fusion of neat CNH was maintained in the salogels and was retained after twenty cycles of melting and crystallization, demonstrating the robust nature of these energy storage materials.
中文翻译：
具有硼酸酯键的强热可逆水凝胶作为热能储存材料
无机盐水合物是有前途的相变材料（PCM），但在高于其熔点的温度下粘度低，导致在蓄热应用中出现泄漏问题。为了实现一种熔融无机 PCM - 四水合硝酸钙 (CNH) 的形状稳定性 - 这项工作探索了聚乙烯醇 (PVA) 在这种溶剂中的凝胶化以及动态硼酸酯键对水凝胶强度的影响。由于 CNH 中极高的盐含量和水合水的稀缺性，PVA 在熔融 CNH 中而不是在水中发生凝胶化是合理的，从而使 PVA 链之间的分子间氢键成为可能。虽然 CNH 中的纯 PVA 水凝胶较弱，但具有凝胶到溶胶的转变温度（T凝胶) 低于室温，添加少量硼砂 (<∼0.3 wt%) 引入动态共价交联并产生具有T凝胶的水凝胶 tunable over a wide temperature range from 7 to 70 °C. The PVA/borax salogels were about one order of magnitude stronger than their well-known PVA/borax hydrogel counterparts, and, unlike PVA/borax hydrogels, were capable of retaining their shape and preventing leakage of molten CNH. Moreover, the salogels exhibited reversible and repeatable temperature-triggered gel-to-sol transitions and the ability to self-heal. The low polymer and crosslinker concentration also ensured that more than 95% of the heat of fusion of neat CNH was maintained in the salogels and was retained after twenty cycles of melting and crystallization, demonstrating the robust nature of these energy storage materials.
更新日期：2022-09-27
中文翻译：
具有硼酸酯键的强热可逆水凝胶作为热能储存材料
无机盐水合物是有前途的相变材料（PCM），但在高于其熔点的温度下粘度低，导致在蓄热应用中出现泄漏问题。为了实现一种熔融无机 PCM - 四水合硝酸钙 (CNH) 的形状稳定性 - 这项工作探索了聚乙烯醇 (PVA) 在这种溶剂中的凝胶化以及动态硼酸酯键对水凝胶强度的影响。由于 CNH 中极高的盐含量和水合水的稀缺性，PVA 在熔融 CNH 中而不是在水中发生凝胶化是合理的，从而使 PVA 链之间的分子间氢键成为可能。虽然 CNH 中的纯 PVA 水凝胶较弱，但具有凝胶到溶胶的转变温度（T凝胶) 低于室温，添加少量硼砂 (<∼0.3 wt%) 引入动态共价交联并产生具有T凝胶的水凝胶 tunable over a wide temperature range from 7 to 70 °C. The PVA/borax salogels were about one order of magnitude stronger than their well-known PVA/borax hydrogel counterparts, and, unlike PVA/borax hydrogels, were capable of retaining their shape and preventing leakage of molten CNH. Moreover, the salogels exhibited reversible and repeatable temperature-triggered gel-to-sol transitions and the ability to self-heal. The low polymer and crosslinker concentration also ensured that more than 95% of the heat of fusion of neat CNH was maintained in the salogels and was retained after twenty cycles of melting and crystallization, demonstrating the robust nature of these energy storage materials.
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