Molecular Dynamics Study of Optically Controlled Phase Change Materials

Abstract

The optically controlled phase change technology makes the phase change material produce an obvious energy barrier between a solid and a liquid, which can effectively prevent spontaneous heat loss. Based on the molecular dynamics method, the microscopic model of the optically controlled composite system (capric acid/4-(phenyldiazenyl)phenyl decanoate) was established and the simulation of the AZO trans−cis isomerization process was based on the modification of the dihedral angle parameters of AZO in the condensed phase. A theoretical method for predicting the temperature of optically controlled phase transition was proposed, and the reason for the temperature difference caused by isomerization was analyzed. At a given molar concentration (30 mol %), the cis and trans phase transition temperature, which shows a temperature difference of 4.49 K, results from the destruction of molecular symmetry and the differences in the aggregation and nucleation ability of the dopant before and after photoisomerization. Experiments verify the reliability of the method. In addition, the analysis of the thermal conductivity of the composite systems was conducted based on the nonequilibrium molecular dynamics method. No matter whether the azophenyl group is a cis structure or a trans structure, doping slightly weakens the thermal conductivity of the raw material due to the destruction of the ordered lattice structure. Aggregation and nucleation of trans-azophenyl groups lead to a higher degree of order of the fatty acid chain than that of the corresponding cis system, resulting in higher thermal conductivity, which can be explained quantitatively by the order parameter. This study provides theoretical support for the thermophysical properties and formation reasons of optically controlled phase change materials containing the azophenyl group and provides ideas for the improvement, development, and application of such materials in the future.

Optimizing the performance of phase-change azobenzene: from trial and error to machine learning

“…In addition, it was found that the chain length and side chain density of the polymer also have an effect on the thermal conductivity. Wang et al 174 investigated the physical properties and temperature differences during the isomerization process of phase change materials doped with Azo. As shown in Fig.…”

Optically Controlled Solid-to-Liquid Phase Transition Materials Based on Azo Compounds

“…60 The thermal conductivity 111 and solubility 56 of the materials are also changed along with the liquefaction process, which is mainly caused by the isomerization leading to the reduction of the degree of symmetry order or the change in polarity. 115 The solid to liquid phase transition of small molecule azo crystals or azopolymers could also be utilized in switching of gas adsorption, 54 nanowetting, 149 and emission-switchable fluorescence. 150 through the phase transition process (Figure 22).…”

“…In addition, if their crystallization points are higher than room temperature, the problem of spontaneous heat loss after charging is serious, which can be optimized by combining the azo solid–liquid OPTMs and the organic PCMs, to simultaneously store the photon energy and ambient thermal energy. Such an elegant combination strategy leads to a win–win situation . As shown in Figure a, Han et al introduced azo compounds into an organic PCM (tridecanoic acid) in the form of dopants. , To ensure a sufficiently high miscibility, the azo compound was functionalized with a tridecanoic ester group.…”

“…In addition, opaque and transparent switching optical devices, such as a smart shutter, can be achieved because the transmittance of materials is significantly improved after liquefaction. , A semicrystalline azopolymer (Table , entry 8) not only can be developed into a smart window with photoswitchable transmittance but also possesses self-healing capability (Figure ). The thermal conductivity and solubility of the materials are also changed along with the liquefaction process, which is mainly caused by the isomerization leading to the reduction of the degree of symmetry order or the change in polarity …”

“…Such an elegant combination strategy leads to a win− win situation. 115 As shown in Figure 10a, Han et al introduced azo compounds into an organic PCM (tridecanoic acid) in the form of dopants. 61,116 To ensure a sufficiently high miscibility, the azo compound was functionalized with a tridecanoic ester group.…”