Molecular Dynamics Study of Optically Controlled Phase Change Materials

Y Wang and SM Wang and J Shi and ZQ Chen and LS Sheng and TT Zhang, JOURNAL OF PHYSICAL CHEMISTRY C, 126, 5443-5456 (2022).

DOI: 10.1021/acs.jpcc.1c10726

The optically controlled phase change technology makes the phase changematerial produce an obvious energy barrier between a solid and a liquid, which can effectivelyprevent spontaneous heat loss. Based on the molecular dynamics method, the microscopicmodel of the optically controlled composite system (capric acid/4-(phenyldiazenyl)phenyldecanoate) was established and the simulation of the AZOtrans-cisisomerization process wasbased on the modification of the dihedral angle parameters of AZO in the condensed phase. Atheoretical method for predicting the temperature of optically controlled phase transition wasproposed, and the reason for the temperature difference caused by isomerization was analyzed.At a given molar concentration (30 mol %), thecisandtransphase transition temperature,which shows a temperature difference of 4.49 K, results from the destruction of molecularsymmetry and the differences in the aggregation and nucleation ability of the dopant before andafter photoisomerization. Experiments verify the reliability of the method. In addition, theanalysis of the thermal conductivity of the composite systems was conducted based on thenonequilibrium molecular dynamics method. No matter whether the azophenyl group is acisstructure or atransstructure, dopingslightly weakens the thermal conductivity of the raw material due to the destruction of the ordered lattice structure. Aggregation andnucleation oftrans-azophenyl groups lead to a higher degree of order of the fatty acid chain than that of the correspondingcissystem, resulting in higher thermal conductivity, which can be explained quantitatively by the order parameter. This study providestheoretical support for the thermophysical properties and formation reasons of optically controlled phase change materialscontaining the azophenyl group and provides ideas for the improvement, development, and application of such materials in thefuture.

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