Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Faculty of Chemical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Langmuir. 2020 Dec 29;36(51):15572-15582. doi: 10.1021/acs.langmuir.0c02960. Epub 2020 Dec 15.
Two organogelators of different chemistry (a fatty acid derivative and a -urea derivative), as well as their blends, were used to impart shape stability to a bio-based phase-change material (PCM) bearing a near-ambient phase-transition temperature. Characterization of the individual gelators and their blends revealed their ability to immobilize the PCM by forming a continuous fibrillar network. The fibrils formed by the fatty acid derivative were helical, while the -urea derivative formed smooth fibrils. Also, the -urea derivative formed a continuous network at a lower critical concentration than the fatty acid derivative. At each fixed concentration, the -urea derivative yielded gels with higher thermal stability than the fatty acid derivative. The two gelators blended in certain ratios demonstrated a strong synergistic effect, providing gels with a significantly higher modulus (∼20-fold) and yield stress (∼1.5-fold) than each gelator individually. PCM gelation did not significantly affect its thermal behavior, however, affected its crystalline morphology. The gelled PCM displayed stacked structures, consisting of alternating pure PCM layers separated by layers formed by gelator fibrils. The phase diagram of the triple system comprising both gelators and PCM demonstrated either single or double gelation behavior depending on the composition. These findings may provide guidelines for the development of novel, shape-stable PCMs, which could be of potential use in various thermal energy storage applications.
两种不同化学结构的有机凝胶剂（脂肪酸衍生物和脲衍生物）及其混合物被用于赋予具有近环境相变温度的生物基相变材料（PCM）形状稳定性。对单个凝胶剂及其混合物的表征揭示了它们通过形成连续的纤维状网络来固定 PCM 的能力。脂肪酸衍生物形成的纤维呈螺旋状，而脲衍生物形成光滑的纤维。此外，脲衍生物在较低的临界浓度下形成连续的网络，而脂肪酸衍生物则在较高的浓度下形成。在每个固定浓度下，脲衍生物形成的凝胶比脂肪酸衍生物具有更高的热稳定性。两种凝胶剂以一定比例混合表现出强烈的协同效应，使凝胶的模量（约 20 倍）和屈服应力（约 1.5 倍）显著高于单独的凝胶剂。然而，PCM 凝胶化对其热行为没有显著影响，但会影响其结晶形态。凝胶化的 PCM 显示出堆叠结构，由纯 PCM 层交替组成，由凝胶剂纤维形成的层分隔。包含两种凝胶剂和 PCM 的三元体系的相图根据组成表现出单凝胶或双凝胶行为。这些发现可能为开发新型形状稳定的 PCM 提供指导，这些 PCM 在各种热能存储应用中可能具有潜在用途。
