## 2 Materials and Methods
### Measurement  
In this study, DSC measurements were conducted with a DSC Q 200 from TA Instruments (New Castle, DE, USA) with a temperature accuracy of 0.1 \({}^{\circ}\)C and an enthalpy precision of 0.1% [37; 38]. The samples with weights between 6 and 7 mg were sealed in  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**PCM**} & \multirow{2}{*}{**Reference Melting Temperature**} & \multicolumn{2}{c}{**Phase**} \\ \cline{3-4}  & & **As-Received** & **Treated** \\ \hline
**Specimen 1** & 21 \({}^{\circ}\)C & Liquid & - \\ \hline  & & Solid & - \\ \hline  & & Solid/Liquid & Liquid \\ \hline  & & 26 \({}^{\circ}\)C & Solid & - \\ \hline  & & & \\ \hline  & & & \\ \end{tabular}
\end{table}
Table 1: Phase of specimens at room temperature.  
Figure 1: FTIR spectra of the PCMs: (**a**) reference MnCl\({}_{2}\), (**b**) specimen 1, (**c**) specimen 2, (**d**) specimen 3, and (**e**) specimen 4.  
aluminum pans and lids, and were measured in a chamber purged with nitrogen. The temperature profile for DSC temperature is given in Figure 2.  
The first step was a holding stage in which the sample was held for 1 min at 15 \({}^{\circ}\)C to stabilize the test chamber temperature. The second step was a heating stage in which the sample was heated from 15 to 105 \({}^{\circ}\)C with a heating rate of 5 \({}^{\circ}\)C/min. The third step was a holding stage in which the sample was held for 1 min at 105 \({}^{\circ}\)C to stabilize the chamber temperature. The last step was a cooling stage in which the sample was cooled from 105 to \(-\)40 \({}^{\circ}\)C with a cooling rate of 5 \({}^{\circ}\)C/min. The thermophysical properties of the PCMs were measured three times per condition. The phase change of PCMs occurs within a temperature range, but the peak temperature in a DSC thermogram was defined as the melting temperature under the endothermic process, or the solidification temperature under the exothermic process in this study.  
The thermal conductivity of a PCM is an important factor in assessing the thermal performance of PCMs in the solid-state or liquid state [39]. In this study, a heat flow meter FOX 314 from TA Instruments was used to measure the thermal conductivities of the PCMs. The heat flow meter was designed to conform to the ASTM C 518-04 [40].  
The thermal conductivities of PCMs having only single phase (either liquid or solid phase) were measured under the conditions in Table 2. The temperature of the lower plate was higher than that of the upper plate, and high sensitivity heat flow transducers and thermocouples were attached to both plates. Moreover, the heat flow equipment can measure thermal conductivity with a resolution of 0.6 \(\upmu\)V and the thickness of the sample with an accuracy of 0.025 mm.  
Thermal diffusivity indicates the ability of a material to transfer thermal energy. Accurate measurement of thermal diffusivity is necessary to make applications and control thermal energy for materials which have conduction, insulation, or have with  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**PCMs**} & \multicolumn{2}{c}{**Temperature for Liquid Phase**} & \multicolumn{2}{c}{**Temperature for Solid Phase**} \\  & \multicolumn{2}{c}{**Conductivity (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Conductivity (\({}^{\circ}\)C)**} \\ \cline{2-5}  & **Upper Plate** & **Lower Plate** & **Upper Plate** & **Lower Plate** \\ \hline Specim 1 & 21 & 35 & 14 & 26 \\ Specim 2 & 21 & 35 & 14 & 26 \\ Specim 3 & 33 & 43 & 21 & 31 \\ Specim 4 & 39 & 49 & 31 & 41 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Temperature conditions for measuring thermal conductivities.  
Figure 2: Dynamic DSC testing temperature profile.  
The thermal diffusivity is given by  
\[\alpha=\frac{k}{\rho C_{p}} \tag{1}\]  
where \(\alpha\) is the thermal diffusivity, \(k\) is the thermal conductivity, \(\rho\) is the density, and \(C_{p}\) is the specific heat capacity.