# Development and investigation of biobased binary eutectic phase change materials for low-temperature building applications: 1-Hexadecanol/1-Dodecanol and 1-Octadecanol/1-Dodecanol

Dehong Li, Thomas Lenfant, Véronic Landry, Denis Rodrigue, Alireza Kaboorani, Xiadong Alice Wang

► To cite this version:

Dehong Li, Thomas Lenfant, Véronic Landry, Denis Rodrigue, Alireza Kaboorani, et al. Development and investigation of biobased binary eutectic phase change materials for low-temperature building applications: 1-Hexadecanol/1-Dodecanol and 1-Octadecanol/1-Dodecanol. Journal of Energy Storage, 2024, 103, pp.114345. 10.1016/j.est.2024.114345. hal-05095498

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Research papers

# Development and investigation of biobased binary eutectic phase change materials for low-temperature building applications: 1-Hexadecanol/ 1-Dodecanol and 1-Octadecanol/1-Dodecanol

Dehong Li<sup>a</sup>, Thomas Lenfant<sup>b</sup>, Véronic Landry<sup>a</sup>, Denis Rodrigue<sup>c</sup>, Alireza Kaboorani<sup>d</sup>, Xiaodong (Alice) Wang<sup>a,*</sup>

<figure><img src="image_3.png" /></figure>

## ARTICLE INFO

### Keywords:

Thermal management

Low-temperature buildings

Fatty alcohols

Eutectic PCMs

No supercooling

## ABSTRACT

Phase change materials (PCMs) play a crucial role in optimizing thermal management in low-temperature buildings, contributing to reduced energy consumption and greenhouse gas emissions. This study aims to address the limitations of conventional paraffin-based PCM by developing binary mixtures of fatty alcohols. Through theoretical calculations, binary phase diagram fitting, and experimental validation, the thermal performance, phase transition behavior, and integration methods of these mixtures were thoroughly investigated using techniques such as differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The results showed that 1-dodecanol/1-tetradecanol (TD) mixtures were unsuitable for building applications due to their inability to form eutectic phases. However, two eutectic PCMs, namely HD82.44 (82.44 % 1-dodecanol/17.56 % 1-hexadecanol) and OD82.66 (82.66 % 1-dodecanol/17.34 % 1-octadecanol), were successfully synthesized. HD82.44 began melting at 16.4 °C, reached peak heat absorption at 19.6 °C and a melting latent heat of 193.7 J/g. Solidification started at 17.3 °C, with two exothermic peaks at 14.2 °C and 6.8 °C, and a freezing latent heat of 192.4 J/g. The solid and liquid specific heats were 2.02 J/(g·°C) and 2.56 J/(g·°C), respectively. OD82.66 began melting at 18.1 °C, with peak thermal effect at 21.4 °C. Solidification started at 23.1 °C, followed by a freezing peak at 15.1 °C. Both melting and freezing enthalpies were 206.4 J/g. Its solid and liquid specific heats were 2.02 J/(g·°C) and 2.67 J/(g·°C), respectively. Both PCM displayed no supercooling, suitable phase change temperatures, and high thermal storage properties, making them promising alternatives to traditional paraffin-based PCM for thermal energy storage in buildings. Additionally, FTIR analysis confirmed the physical integration of the binary fatty alcohol eutectic PCMs, while thermal cycling tests demonstrated their long-term stability.

## List of abbreviations

<table><thead><tr><td>Abbreviation</td><td>Full form</td></tr></thead><tbody><tr><td>IEA</td><td>International Energy Agency</td></tr><tr><td>PCMs</td><td>Phase change materials</td></tr><tr><td>SHTES</td><td>Sensible heat thermal storage</td></tr><tr><td>LHTES</td><td>Latent heat thermal energy storage</td></tr><tr><td>BPCMs</td><td>Biobased phase change materials</td></tr><tr><td>DSC</td><td>Differential scanning calorimetry</td></tr></tbody></table>

(continued on next column)

(continued)

<table><thead><tr><td>Abbreviation</td><td>Full form</td></tr></thead><tbody><tr><td>FTIR</td><td>Fourier transform infrared spectroscopy</td></tr><tr><td>ATR</td><td>Attenuated total reflection</td></tr><tr><td>T<sub>m</sub>, onset</td><td>Onset melting temperature (°C)</td></tr><tr><td>T<sub>m</sub></td><td>Melting peak temperature (°C)</td></tr><tr><td>ΔH<sub>m</sub></td><td>Melting latent heat (J/g)</td></tr><tr><td>T<sub>m</sub>, endset</td><td>Endset melting temperature (°C)</td></tr><tr><td>T<sub>f</sub>, onset</td><td>Onset freezing temperature (°C)</td></tr></tbody></table>

(continued on next page)

<footnote><sup>a</sup> Centre de recherche sur les matériaux renouvelables, Département des sciences du bois et de la forêt, Faculté de foresterie, de géographie et de géomatique, Université Laval, 2425 Rue de la Terrasse, Québec G1V 0A6, Canada</footnote>

<footnote><sup>b</sup> Université de Montpellier, Pl. Eugène Bataillon, Montpellier, 34090, France</footnote>

<footnote><sup>c</sup> Department of Chemical Engineering, Université Laval, 1065 Avenue de la Médecine, Québec G1V 0A6, Canada</footnote>

<footnote><sup>d</sup> Building Efficiency Technology Access Centre, Red River College, Winnipeg R3H 0J9, Canada</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: xiaodong.wang@sbf.ulaval.ca (X.(A. Wang)).</footnote>
(continued)

<table><thead><tr><th>Abbreviation</th><th>Full form</th></tr></thead><tbody><tr><td>T<sub>f</sub></td><td>Freezing peak temperature (°C)</td></tr><tr><td>T<sub>f, endset</sub></td><td>Endset freezing temperature (°C)</td></tr><tr><td>ΔH<sub>f</sub></td><td>Freezing latent heat (J/g)</td></tr><tr><td>C<sub>ps</sub></td><td>Solid constant-pressure specific heat capacity (J/(g·°C))</td></tr><tr><td>C<sub>p, peak</sub></td><td>Peak constant-pressure specific heat capacity (J/(g·°C))</td></tr><tr><td>C<sub>pl</sub></td><td>Liquid constant-pressure specific heat capacity (J/(g·°C))</td></tr></tbody></table>

# 1. Introduction

According to the 2022 report by the international energy agency (IEA), building operations account for 30 % of the global energy consumption and contribute 26 % of global energy-related emissions [1]. Therefore, reducing energy consumption in buildings is crucial for mitigating environmental impacts. In this context, efficient building thermal management technologies have become increasingly crucial for achieving energy savings and sustainability, making the development and application of advanced phase change materials (PCMs) a key focus of current research. PCM can store thermal energy in the form of latent heat, with a volumetric heat storage capacity approximately 5 to 14 times greater than that of sensible heat thermal storage (SHTES) materials like concrete [2]. Due to the high storage capacity and energy density of latent heat thermal energy storage (LHTES), PCM has significant potential to reduce residential energy demand, particularly because they can store and release large amounts of energy at nearly constant temperatures during phase transitions.

Developing PCMs suitable for the range of temperature associated with building is a challenging task. According to Hu et al. [3], the optimal indoor equilibrium temperature should be between 17.3 °C and 22.0 °C. Although several investigations have focused on paraffins with suitable melting temperatures, significant environmental concern are associated with their production, processing, and disposal. Paraffins, being petroleum by-products, pose environmental risks, including land, water, and air pollution, as well as concerns during disposal [4]. In the pursuit of more sustainable solutions, alternative renewable and pollution-free material sources are essential to reduce the consumption of finite resources (mainly petroleum).

Biobased phase change materials (BPCMs), extracted from plant oils (such as soybean oil, coconut oil, and palm oil) and animal fats (such as beef tallow), offer a promising source of high energy storage capacity and sustainability. These materials have high potential to improve thermal comfort and energy efficiency in buildings. Their main constituents include biobased fatty acids, esters, and alcohols. Fatty acids exhibit long-term stability, minimal supercooling, and negligible volume changes during phase transition. Esters, on the other hand, offer advantages such as low cost, good chemical stability, non-corrosiveness with other building materials, and non-flammability. Sugar alcohols are known for their high latent heat and non-toxicity. However, in all cases, the main limitation for building applications lies in their melting temperatures not always matching the comfort temperatures of buildings and supercooling [5,6].

Eutectic PCMs are unique combinations of two or more substances with distinct melting points. Such mixtures typically present a melting point lower than that of each individual component [7,8]. Eutectic PCM not only exhibits flexibility of the phase transition temperature, but also has high latent heat, leading to more effective thermal management in low-temperature building environments. For example, Chinnasamy and Appukuttan [9] prepared a binary eutectic mixture consisting of lauric acid (40 %) and myristyl alcohol (60 %) to determine their thermal performances. Differential scanning calorimetry (DSC) results indicated that the melting temperature and latent heat of the developed PCM were 21.3 °C and 151.5 J/g, respectively, while the solidification temperature and its latent heat were found to be 19.9 °C and 151.6 kJ/kg,

respectively. Shilei et al. [10] synthesized a binary eutectic PCM using capric acid and lauric acid in a 65:35 M ratio, showing a phase transition temperature of 19.7 °C and a melting latent heat of 126.6 J/g. This PCM was then incorporated into wall panels, resulting in a composite phase change energy storage wall panel with a melting temperature of 21.0 °C and a melting latent heat of 35.2 J/g. This composite showed thermal stability up to 360 thermal cycles, which confirmed its suitability for energy-efficient construction. Fauzi et al. [11] prepared an eutectic PCM with a phase transition temperature of 46.7 °C and a high latent heat of 155.4 J/g. The PCM was composed of myristic acid and palmitic acid (70:30). Liu et al. [12] developed a ternary eutectic PCM based on lauric acid/myristic acid/stearic acid (55.8:32.8:11.4) with a melting temperature of 29.0 °C and a melting latent heat of 137.1 J/g. Currently, research on BPCMs mainly focuses on fatty acid/fatty acid eutectics and fatty acid/alcohol eutectics. However, limited studies have been conducted on alcohol/alcohol eutectic PCM, and these reports lack an in-depth investigation on the phase transition behavior of eutectic PCM.

To enhance the performance of PCMs in low-temperature buildings application, this study investigates four biobased fatty alcohols with high latent heat to develop two novel binary eutectic PCM with melting temperatures ranging from 17.3 to 22.0 °C [3]. The primary goal of this research is to evaluate the thermal storage capacity, phase transition behavior, and synthesis mechanisms of these fatty alcohol-based eutectic PCM, as well as to thoroughly assess their thermal stability through thermal cycling tests in low-temperature environments. The study aims to expand the available options for low-temperature building applications and offer scientific and reliable support for the design and implementation of future low-carbon, sustainable construction.

# 2. Experimental

## 2.1. Materials

The selected fatty alcohols, 1-dodecanol (98 %; T<sub>m</sub> = 24.1 °C, ΔH<sub>m</sub> = 221.0 J/g), 1-tetradecanol (97 + %; T<sub>m</sub> = 39.1 °C, ΔH<sub>m</sub> = 230.9 J/g), 1-hexadecanol (98 %; T<sub>m</sub> = 50.2 °C, ΔH<sub>m</sub> = 243.6 J/g), and 1-octadecanol (97 %; T<sub>m</sub> = 59.1 °C, ΔH<sub>m</sub> = 243.1 J/g), were purchased from Thermo Fisher Scientific (USA) and used as received.

## 2.2. Theoretical eutectic point calculation

According to the second law of thermodynamics and the phase equilibrium theory, the melting temperature of eutectic PCM can be calculated as [8,13]:

$$T_m = \left[ \frac{1}{T_i} - \frac{R \ln(x_i)}{\Delta H_i} \right]^{-1} \quad i = A, B \quad (1)$$

where T<sub>m</sub> is the melting point of the eutectic mixture, while T<sub>i</sub> and ΔH<sub>i</sub> are the melting points and melting latent heats of component i. x<sub>i</sub> is the mole fraction of each component (x<sub>A</sub> + x<sub>B</sub> = 1), and R is the ideal gas constant (8.314 J/(mol·K)).

## 2.3. Preparation of biobased fatty alcohol eutectic PCMs

Place 20 % 1-dodecanol and 80 % 1-tetradecanol (molar ratio) PCMs into two separate beakers. Then, heat the samples on two magnetic heaters set to 70 °C until fully melted. Add the melted 1-tetradecanol into the 1-dodecanol beaker and stir magnetically at 40 °C and 200 rpm for 20 min. The mixture was collected and coded as TD20 where “T” represents component 1-tetradecanol, “D” represents for component 1-dodecanol, and “20” represents for the molar content of 1-dodecanol in the mixture. 1-Dodecanol was always used as a component and a series of TD mixtures with different molar ratios as well as HD and OD mixtures were prepared using the same protocol.
<figure><img src="image_4.png" /><figcaption>Fig. 1. DSC melting and solidification curves of four fatty alcohol raw materials.</figcaption></figure>

## 2.4. Differential scanning calorimetry (DSC)

Differential scanning calorimetry (DSC) is an experimental technique to quantify the heat released or absorbed by a sample during temperature changes. This method provides vital thermal parameters for PCM, such as the phase transition temperature, latent heat of phase transition, and specific heat, among others. The mixture samples were first dried at 40 °C for 2 h to remove any humidity. The testing was carried out using a Q1000 instrument (TA Instruments, USA), with indium serving as the calibration material for temperature and latent heat. Aluminum sample pans and lids were used to place 5 to 12 mg of sample. Three test samples were prepared for each PCM mixture. The system was purged with nitrogen gas at 20 mL/min. Each test sample was subjected to the heating 1, cooling 1 and heating 2 processes. Heating 1 aimed to eliminate the thermal history of the material, while cooling 1 and heating 2 were dedicated to analyze the solidification and melting behavior of the material. All results are presented as an average of three tests. The specific heating and cooling procedures were as follows:

* Equilibrate at -20.0 °C.

* Ramp 5.0 °C/min to 80.0 °C.

* Wait for 1.0 min.

* Mark end of heating 1.

* Ramp 5.0 °C/min to -20.0 °C.

* Wait for 1.0 min.

* Mark end of cooling 1.

* Ramp 5.0 °C/min to 80.0 °C.

* Mark end of heating 2.

## 2.5. Fourier transform infrared spectroscopy (FTIR)

Fourier transform infrared spectroscopy (FTIR) is a technique to monitor the vibrations of functional groups, thus elucidating the molecular structure. The same drying process as for DSC was used. Then, recorded with an INVENIO® R (Bruker Optics Inc., Billerica, USA)

infrared spectrometer and measured using the attenuated total reflection (ATR) technique. Each sample underwent 32 scans across a range of 400 to 4000 cm⁻¹ with a resolution of 4 cm⁻¹.

## 2.6. Thermal cycling test for assessing the stability of eutectic fatty alcohol PCM

Add 5 mL of PCM to a test tube and insert a thermometer into the center of the liquid to monitor the temperature changes of the PCM. The PCM was heated to 40 °C using a hot water bath and then cooled to 10 °C using an ice water bath, completing one thermal cycle. Each PCM sample undergoes 3 parallel thermal cycling tests. To verify the short-term and long-term stability of the PCM, 50 and 200 thermal cycles were conducted, respectively. After the thermal cycling, the liquid state was observed, and the DSC curves of the PCM at the top, middle, and bottom of the test tube were measured to assess the impact of thermal cycling on the thermal performance uniformity and stability of the PCM.

# 3. Results and discussion

## 3.1. Thermal properties of four fatty alcohol raw materials and calculation of theoretical eutectic point of binary fatty alcohols

To design biobased eutectic PCMs with excellent thermal properties, four biobased fatty alcohols were selected as raw materials: 1-dodecanol, 1-tetradecanol, 1-hexadecanol, and 1-octadecanol. These fatty alcohol compounds exhibited good chemical stability and phase change performance.

First, the melting and solidification curves of the four raw materials were measured using DSC, and the results are shown in Fig. 1. The melting curve illustrated the PCMs' transition from solid to liquid at their respective melting temperatures. This phase transition behavior was characterized by a single endothermic peak. In contrast, the solidification process appeared to be more complex, especially for 1-tetradecanol and 1-hexadecanol. As the temperature began to decrease, the first solidification peak appeared, marking the onset of crystallization and the liquid-to-solid phase transition. With the continued decrease in temperature, the phenomenon of supercooling caused the liquid to rapidly crystallize in a short time, releasing a large amount of latent heat. This resulted in a sharp and brief rise in temperature on the solidification curve, corresponding to the second solidification peak. The third solidification peak may have been related to the crystallization of the remaining liquid or the rearrangement of the crystal structure. The entire process demonstrated the complexity of multi-step solidification, each accompanied by different forms of heat release. The specific thermal performance parameters of the four fatty alcohol raw materials are shown in Table 1. Among them, 1-dodecanol and 1-tetradecanol had relatively low melting peak temperatures of 24.1 °C and 39.2 °C, respectively. 1-hexadecanol and 1-octadecanol had higher melting peak temperatures of 50.2 °C and 59.1 °C, respectively. The phase change temperatures of these materials are all higher than the indoor equilibrium temperature (17.3 °C to 22.0 °C), requiring further optimization. In addition, 1-hexadecanol had the highest latent heat, indicating its greater capacity for thermal energy storage during phase change.

<table><caption>**Table 1**

Thermal properties of four fatty alcohol raw materials.</caption><thead><tr><th>Materials</th><th>T<sub>m, onset</sub> (°C)</th><th>T<sub>m, 1st</sub> (°C)</th><th>T<sub>m, endset</sub> (°C)</th><th>ΔH<sub>m</sub> (J/g)</th><th>T<sub>f, onset</sub> (°C)</th><th>T<sub>f, 1st</sub> (°C)</th><th>T<sub>f, 2nd</sub> (°C)</th><th>T<sub>f, 3rd</sub> (°C)</th><th>T<sub>f, endset</sub> (°C)</th><th>ΔH<sub>f</sub> (J/g)</th></tr></thead><tbody><tr><td>1-dodecanol</td><td>15.5</td><td>24.1</td><td>29.7</td><td>220.9</td><td>20.7</td><td>19.4</td><td>-</td><td>-</td><td>11.3</td><td>221.0</td></tr><tr><td>1-tetradecanol</td><td>36.3</td><td>39.2</td><td>45.0</td><td>229.2</td><td>36.1</td><td>33.8</td><td>32.8</td><td>32.3</td><td>27.7</td><td>230.9</td></tr><tr><td>1-hexadecanol</td><td>44.4</td><td>50.2</td><td>56.0</td><td>244.7</td><td>47.8</td><td>45.7</td><td>41.2</td><td>40.1</td><td>35.8</td><td>243.6</td></tr><tr><td>1-octadecanol</td><td>55.8</td><td>59.1</td><td>64.8</td><td>242.9</td><td>56.3</td><td>53.9</td><td>49.7</td><td>-</td><td>45.1</td><td>243.1</td></tr></tbody></table>

T<sub>m, onset</sub>: Onset melting temperature; T<sub>m, 1st</sub>: First melting peak temperature; T<sub>m, endset</sub>: Endset melting temperature; ΔH<sub>m</sub>: Melting latent heat; T<sub>f, onset</sub>: Onset freezing temperature; T<sub>f, 1st</sub>: First freezing peak temperature; T<sub>f, 2nd</sub>: Second freezing peak temperature; T<sub>f, 3rd</sub>: Third freezing peak temperature; T<sub>f, endset</sub>: Endset freezing temperature; ΔH<sub>f</sub>: Freezing latent heat.
<figure><img src="image_5.png" /><figcaption>Fig. 2. Binary solid-liquid equilibrium phase diagrams of: (a) TD, (b) HD, and (c) OD mixtures.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 3. DSC melting curves illustrating eutectic behavior of (a) TD, (b) HD, and (c) OD mixtures at various molar ratios; (d, e) Binary eutectic phase diagrams and corresponding fitting results for HD and OD PCMs; (f, g) Tammann plots for fitting and predicting the melting latent heat of HD and OD PCMs.</figcaption></figure>

Based on thermodynamic theory, the melting temperatures of these materials at various molar mixing ratios were calculated using Eq. (1), and binary solid-liquid equilibrium phase diagrams were plotted (Figs. 2a-c). In these phase diagrams, the eutectic point corresponds to the temperature at which the liquid phase directly transforms into two solid phases, where the melt and both solid phases coexist. By accurately determining the positions of these intersection points, the eutectic points for different material combinations can be predicted. In a TD mixture containing 20% 1-dodecanol, both 1-tetradecanol and 1-dodecanol exist

in the liquid state above the liquidus line. Between the liquidus and solidus lines, 1-tetradecanol solidifies while 1-dodecanol remains in the liquid state. Below the solidus line, both components solidify. Conversely, in a mixture with 90% 1-dodecanol, 1-dodecanol remains liquid, while 1-tetradecanol solidifies between the liquidus and solidus lines. When the molar content of 1-dodecanol is 74%, both components to melt simultaneously at 18.8 °C. Fig. 2b and c show that eutectic PCMs also can be formed in HD and OD mixtures with 1-dodecanol molar contents of 88% and 95%, respectively, with the corresponding
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** DSC melting and solidification curves (a), constant-pressure specific heat capacity as a function of temperature (b), and enthalpy as a function of temperature during the melting (c) and solidification (d) processes for fatty alcohol PCMs.</figcaption></figure>

theoretical eutectic melting temperatures being 21.9 °C and 23.2 °C.

## 3.2. Melting behavior analysis and optimal ratio fitting of fatty alcohol PCM mixtures

Given the nature of eutectic mixtures, the accurate determination of the eutectic composition holds a paramount importance to ensure consistent performance and long-term stability. Consequently, experiments were conducted around the theoretical eutectic point until a fatty alcohol PCM mixture exhibited a distinct melting peak and high latent heat was identified [14]. To do so, a series of TD, HD, and OD mixtures were prepared close to their theoretical eutectic molar ratio, which served as the central point. Based on these samples, a complete DSC characterization was performed, and the curves are reported in Fig. 3.

Fig. 3a showed that for TD mixtures, as the temperature increased, a small melting peak (Region I) and a slightly larger melting peak (Region II) initially emerged. This may have been the result of solid-solid phase transitions [15], typically associated with crystallization and polymorphic transitions within this temperature range, resulting in this thermal response and the formation of melting peaks in the DSC curve. At low temperatures, the components may have undergone some form of ordered structure. Region III represented the main eutectic melting peak region for the TD mixtures, encompassing the whole eutectic melting process of the system. At the eutectic temperature, both components began melting simultaneously, resulting in a broad peak in the DSC curve. This peak served as the primary endothermic peak for the TD binary PCM. The melting peak in Region IV could be attributed to the melting of the higher melting point component, 1-tetradecanol in this case. After the eutectic mixture melted, the components having the highest melting point may have started to melt independently. The TD mixture in Fig. 3a exhibited solid-solid melting peaks in both low-

temperature regions I and II. Although TD80 had the lowest eutectic phase transition temperature, it underwent two phase transitions within regions I and II, making it unsuitable for maximizing heat storage for the required temperature range. Additionally, multiple melting peaks indicated poor compatibility and phase separation among the components. Therefore, TD PCM was not suitable as PCM for building energy applications. On the other hand, HD and OD PCMs did not undergo solid-solid phase transitions in the low-temperature region. When the molar content of 1-dodecanol exceeded 60 %, the DSC melting curves of HD and OD PCMs showed a single melting peak. This indicated excellent compatibility between 1-dodecanol, 1-hexadecanol, and 1-octadecanol, allowing for eutectic formation between the components. These mixtures could be suitable for building thermal management materials and were further analyzed.

Based on the melting temperature of PCM mixtures obtained from DSC tests, binary phase diagrams for the HD and OD PCMs were constructed and fitted, as shown in Fig. 3 (d, e). It can be seen from the figure that the eutectic mole fractions of 1-dodecanol in HD and OD PCMs are 82.44 % and 82.66 %, respectively. Correspondingly, the eutectic melting temperatures were determined to be 19.7 °C and 21.8 °C, respectively. Characteristic tammann diagrams were constructed through linear regression of the eutectic melting enthalpies against mole fractions to predict the melting enthalpies of the HD and OD eutectic systems, as shown in Fig. 3 (f, g). When the mole fraction of 1-dodecanol exceeds the eutectic mole fraction, only one melting peak appears, making it difficult to accurately distinguish between the eutectic melting peak and the component's melting peak. Therefore, only the PCM melting latent heat closest to the fitted eutectic point was selected as the Tammann fitting data to maximize the accuracy of the fitting results. The fitted melting enthalpies are 186.1 J/g for HD and 172.6 J/g for OD.
<table><caption>**Table 2**
Molar ratios and thermal performance parameters of PCMs.</caption><thead><tr><th>Materials</th><th>Molar ratio</th><th>T<sub>m, onset</sub> (°C)</th><th>T<sub>m, 1st</sub> (°C)</th><th>T<sub>m, endset</sub> (°C)</th><th>ΔH<sub>m</sub> (J/g)</th><th>T<sub>f, onset</sub> (°C)</th><th>T<sub>f, 1st</sub> (°C)</th><th>T<sub>f, 2nd</sub> (°C)</th><th>T<sub>m, endset</sub> (°C)</th><th>ΔH<sub>f</sub> (J/g)</th><th>References</th></tr></thead><tbody><tr><td>HD82.44</td><td>17.56:82.44</td><td>16.4</td><td>19.6</td><td>23.9</td><td>193.7</td><td>17.3</td><td>14.2</td><td>6.8</td><td>-3.8</td><td>192.4</td><td>This work</td></tr><tr><td>OD82.66</td><td>17.34:82.66</td><td>18.1</td><td>21.4</td><td>32.4</td><td>206.4</td><td>23.1</td><td>15.1</td><td>-</td><td>8.4</td><td>206.4</td><td>This work</td></tr><tr><td>Lauric acid/myristyl alcohol</td><td>40:60</td><td>18.78</td><td>21.3</td><td></td><td>151.5</td><td>22.46</td><td>19.9</td><td>13.9</td><td></td><td>151.6</td><td>[9]</td></tr><tr><td>Capric acid/cetyl alcohol</td><td>70:30</td><td>-</td><td>22.9</td><td></td><td>144.9</td><td>-</td><td>12.0</td><td>-</td><td></td><td>145.9</td><td>[16]</td></tr><tr><td>Tetradecanol/capric acid</td><td>38:62</td><td>19.13</td><td>22.7</td><td></td><td>153.4</td><td>13.32</td><td>11.9</td><td>-</td><td></td><td>147.8</td><td>[17]</td></tr><tr><td>Tetradecanol/lauric acid</td><td>53.6:46.4</td><td>24.40</td><td>26.6</td><td></td><td>162.7</td><td>24.43</td><td>21.9</td><td>-</td><td></td><td>146.8</td><td>[17]</td></tr><tr><td>Decanoic acid/tetradecanoic acid</td><td>82:18</td><td>-</td><td>20.5</td><td></td><td>153.0</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[18]</td></tr><tr><td>Capric acid/lauric acid</td><td>65.12:34.88</td><td>19.7</td><td>21.3</td><td></td><td>126.6</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[10]</td></tr><tr><td>Capric acid / palmitic acid / stearic acid</td><td></td><td></td><td>22.1</td><td></td><td>139.3</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[19]</td></tr><tr><td>Paraffin RT27</td><td>100</td><td>-</td><td>26.5</td><td></td><td>189.0</td><td>-</td><td>24.5</td><td>-</td><td></td><td>-</td><td>[20]</td></tr><tr><td>Paraffin RT35</td><td>100</td><td>-</td><td>35.0</td><td></td><td>157.0</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[21]</td></tr><tr><td>Paraffin RT42</td><td>100</td><td>-</td><td>43.0</td><td></td><td>174.0</td><td>-</td><td>38.0</td><td>-</td><td></td><td>-</td><td>[22]</td></tr><tr><td>Paraffin RT55</td><td>100</td><td>-</td><td>55.0</td><td></td><td>170.0</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[23]</td></tr><tr><td>Paraffin RT70</td><td>100</td><td>-</td><td>70.0</td><td></td><td>260.0</td><td>-</td><td>-</td><td>-</td><td></td><td>-</td><td>[23]</td></tr></tbody></table>

T<sub>m, onset</sub>: Onset melting temperature; T<sub>m, 1st</sub>: First melting peak temperature; T<sub>m, endset</sub>: Endset melting temperature; ΔH<sub>m</sub>: Melting latent heat; T<sub>f, onset</sub>: Onset freezing temperature; T<sub>f, 1st</sub>: First freezing peak temperature; T<sub>f, 2nd</sub>: Second freezing peak temperature; T<sub>f, endset</sub>: Endset freezing temperature; ΔH<sub>f</sub>: Freezing latent heat.

### 3.3. Thermal performance and error analysis of eutectic fatty alcohol PCMs

The HD82.44 and OD82.66 PCM were prepared based on the fitted eutectic molar ratio. The DSC results are presented in Fig. 4a, with the specific parameters reported in Table 2. It can be seen from the Fig. 4a, both eutectic PCM have suitable phase transition temperatures (17.3–22.0 °C [3]). HD82.44 started melting at 16.4 °C, with its highest heat absorption observed at 19.6 °C, and its melting endset temperature recorded at 23.9 °C. Similarly, OD82.66 began melting at 18.1 °C and reached its peak thermal effect at 21.4 °C, and its melting endset temperature was 32.4 °C. Both exhibited a single melting peak, signifying the formation of a stable eutectic composition where all components melt simultaneously at a well-defined temperature. Analyzing the solidification curves of the PCM, HD82.44 began freezing as the temperature dropped to 17.3 °C and exhibited a prominent solidification peak at 14.2 °C, representing the crystallization process of the whole eutectic system. In the liquid state at higher temperature, the HD mixture gradually crystallized into a solid as the temperature decreased. A small solidification peak appeared at 6.8 °C, possibly indicating a solid-solid phase transition of HD components or a liquid-solid phase transition in locally uncrystallized liquid, coupled with some rearrangement of crystals or crystallites. The freezing endset temperature of HD82.44 was –3.8 °C. On the other hand, OD82.66 began solidifying at 23.1 °C and showed only one significant solidification peak at 15.1 °C, making it highly suitable for building applications as both components could solidify and release heat at the same temperature. OD82.66's freezing endset temperature was 8.4 °C.

To further investigate the phase transition behavior of eutectic PCMs, the enthalpy changes with temperature were plotted in Fig. 4(c, d). Fig. 4c shows that during melting, as the temperature increases, PCMs initially store heat in the form of solid sensible heat, with relatively low energy storage capacity. However, as the temperature approaches 20 °C, the PCM gradually transitions into a liquid state while storing thermal energy in the form of latent heat, and the enthalpy change of the PCM rapidly increases. HD82.44 stores 193.7 J/g, while OD82.66 stores 206.4 J/g. Compared with the melting enthalpy of 1-dodecanol, the melting enthalpies of HD82.44 and OD82.66 are slightly lower, but still maintain relatively high values, significantly higher than the melting enthalpies of bio-based eutectic PCMs prepared in other studies and most paraffin-based PCMs (Table 2). After the phase transition, all PCM transform into a liquid state, and further heating then stores heat in the form of liquid sensible heat, which has a smaller heat storage capacity. Fig. 4d shows that slight undercooling is present during the solidification of 1-dodecanol, which was not observed in the

<table><caption>**Table 3**
Constant-pressure specific heat capacity parameters of PCMs.</caption><thead><tr><th rowspan="2">Materials</th><th colspan="3">C<sub>p</sub> (J/(g·°C))</th><th rowspan="2">References</th></tr><tr><th>C<sub>ps</sub></th><th>C<sub>p, peak</sub></th><th>C<sub>pl</sub></th></tr></thead><tbody><tr><td>1-dodecanol</td><td>1.84 (0 °C)</td><td>64.15 (24 °C)</td><td>2.65 (40 °C)</td><td>This work</td></tr><tr><td>1-hexadecanol</td><td>1.77 (20 °C)</td><td>54.54 (49 °C)</td><td>2.70 (80 °C)</td><td>This work</td></tr><tr><td>1-octadecanol</td><td>1.63 (20 °C)</td><td>54.84 (58 °C)</td><td>2.55 (80 °C)</td><td>This work</td></tr><tr><td>HD82.44</td><td>2.02 (0 °C)</td><td>44.30 (19 °C)</td><td>2.56 (40 °C)</td><td>This work</td></tr><tr><td>OD82.66</td><td>2.02 (0 °C)</td><td>41.38 (21 °C)</td><td>2.67 (40 °C)</td><td>This work</td></tr><tr><td>Hexadecane</td><td>-</td><td>-</td><td>2.21</td><td>[24]</td></tr><tr><td>Heptadecane</td><td>-</td><td>-</td><td>2.22</td><td>[24]</td></tr><tr><td>Octadecane</td><td>1.91</td><td>-</td><td>2.22</td><td>[24]</td></tr><tr><td>Nonadecane</td><td>1.92</td><td>-</td><td>2.30</td><td>[24]</td></tr><tr><td>Eicosane</td><td>1.93</td><td>-</td><td>2.33</td><td>[24]</td></tr><tr><td>Paraffin wax</td><td>2.1</td><td>-</td><td>2.10</td><td>[25]</td></tr><tr><td>Paraffin wax</td><td>2.0</td><td>-</td><td>2.15</td><td>[26]</td></tr><tr><td>Water</td><td>2.1</td><td>-</td><td>4.17 (25 °C)</td><td>[27,28]</td></tr></tbody></table>

C<sub>ps</sub>: Solid constant-pressure specific heat capacity; C<sub>p, peak</sub>: Peak constant-pressure specific heat capacity; C<sub>pl</sub>: Liquid constant-pressure specific heat capacity.

binary eutectic mixtures (HD82.44 and OD82.66). This suggests that eutectic mixtures are advantageous in eliminating material undercooling, which is highly favorable for the exothermic solidification of PCM. The solidification enthalpies of HD82.44 and OD82.66 were as high as 192.4 J/g and 206.4 J/g, respectively. From the HD82.44 curve, two distinct phase transition steps can be observed, confirming the presence of two solidification peaks (6.8 °C and 14.2 °C), as shown in Fig. 4a.

The constant-pressure specific heat capacity (C<sub>p</sub>) is commonly used to characterize the heat absorption or dissipation capability of a substance. Fig. 4b presents the curves for the fatty alcohol PCM as a function of temperature, while the specific parameters were listed in Table 3. The solid-state specific heat capacities of HD82.44 and OD82.66 were both 2.02 J/(g·°C). These values are higher than those of the pure components, indicating that the eutectic PCMs have a higher heat absorption capacity than their pure components in the solid state. The solid-state specific heat is comparable to that of alkanes, paraffins, and water. As the temperature increased, the specific heat of PCM continuously increased. Upon reaching the phase transition temperature range, the material undergoes a state change, leading to significant heat absorption and causing the specific heat to increase within a narrow temperature range rapidly. The specific heat capacity of HD82.44 reached its peak (44.3 J/(g·°C)) at 19 °C, which is 2.92 J/(g·°C) higher than the peak specific heat of OD82.66 at 21 °C. Although the peak specific heat of
<figure><img src="image_8.png" /><figcaption>Fig. 5. (a) FTIR spectra of the fatty alcohol PCMs; (b) DSC melting and solidification curves of HD82.44 PCM before and after thermal cycling; (c) DSC melting and solidification curves of OD82.66 PCM before and after thermal cycling; (d) Photographs of HD82.44 and OD82.66 PCMs after 50 thermal cycles; (e) Photographs of HD82.44 and OD82.66 PCMs after 200 thermal cycles.</figcaption></figure>

HD82.44 and OD82.66 are significantly lower than for 1-dodecanol, their low phase transition temperatures make them more suitable for thermal storage in buildings. As the temperature further increased, all PCM completely melted, and the liquid specific heat capacity of HD82.44 and OD82.66 were 2.56 J/(g·°C) and 2.67 J/(g·°C), respectively. These values were comparable to those of pure components and higher than those of alkanes and paraffins. They reached up to 60 % of the specific heat capacity of water, showing excellent heat absorption capacity.

The experimental phase transition temperatures for HD82.44 and OD82.66 were 19.6 °C and 21.4 °C, respectively. These values closely match the theoretical calculated eutectic temperature with differences less than 3 °C for HD82.44 (21.9 °C) and OD82.66 (23.2 °C). There are also relatively small differences between the theoretical eutectic melting temperatures and the experimental values compared with the eutectic PCM prepared by Kahwaji and White [29] with decanoic and tetradecanoic acids (Theoretical value: 24.9 °C, Experimental value: 20.5 ± 1.5 °C). The theoretical eutectic molar ratio for HD82.44 shows a small difference from the experimental results (Theoretical value: 88:12, Experimental value: 82.44:17.56), is similar to the range reported for published binary fatty acid eutectic PCM [29]. However, the theoretical eutectic molar ratio for OD82.66 significantly deviates from the experimental value (Theoretical value: 95:5, Experimental value: 82.66:17.34). This difference may be attributed to the simplifications made to obtain Eq. (1), which results from Eq. (2). According to the literature, for hydrates and especially aliphatic acids, assuming excess free enthalpies $G_{i,ex} = 0$ are good approximations [30]. The simplified Eq. (1) still maintains high accuracy for the theoretical calculations of fatty acid eutectic PCM. The eutectic PCM prepared by Kahwaji and White [29] with decanoic and tetradecanoic acids shows only a 2 % deviation between the theoretical composition ratio (80:20) and the experimental value (82:18). Although a slight discrepancy was observed in the theoretical composition ratio calculation for the prepared

dodecanoic and tetradecanoic acids eutectic PCM compared to the experimental value (Theoretical value: 65:35, Experimental value: 71:29), it still fell within the difference ranges reported in the literature. In summary, Eq. (1) can be used as a first approximation for the eutectic molar ratio and eutectic temperature of fatty alcohol mixtures. It should be noted that their prediction for the eutectic molar ratio may not always be highly accurate. For more precise results, the excess free enthalpy term should be incorporated into the calculations as:

$$ \left\{ \begin{aligned} & \frac{H_A}{T_A} (T_m - T_A) + RT_m \ln(1 - x_A) + G_{A,ex} = 0 \\ & \frac{H_B}{T_B} (T_m - T_B) + RT_m \ln(1 - x_B) + G_{B,ex} = 0 \end{aligned} \right. \qquad (2) $$

where $G_{A,ex}$ and $G_{B,ex}$ are the excess free enthalpy of components A and B, respectively.

HD82.44 has a $\Delta H_m$ experiment value of 193.7 J/g, which was 7.6 J/g higher than the fitting result obtained from the Tammann plot. Conversely, OD82.66 exhibited a remarkably high $\Delta H_m$ (206.4) J/g, which is 33.8 J/g above the fitted results. This disparity originated from the selection of the eutectic latent heat data during the construction of Tammann plots. Limited latent heat data resulted in low accuracy in the predictions. The final eutectic molar ratios for HD and OD PCM were determined as 82.44:17.56 and 82.66:17.34, respectively.

### 3.4. Integration mechanism analysis and thermal cycling stability of fatty alcohol eutectic PCMs

The changes in functional groups before and after the mixing of PCMs were studied through FTIR to investigate the integration mechanism of binary eutectic PCM. Fig. 5a showed that the main peaks of 1-dodecanol are OH stretching at 3320 cm$^{-1}$, CH aliphatic stretching at 2921 cm$^{-1}$ and 2852 cm$^{-1}$, as well as saturated hydrogen bonds bending
<table><caption>**Table 4**

Thermal performance parameters of HD82.44 and OD82.66 eutectic PCMs before and after thermal cycling.</caption><thead><tr><th>Materials</th><th>Location</th><th>T<sub>m, onset</sub> (°C)</th><th>T<sub>m, 1st</sub> (°C)</th><th>T<sub>m, endset</sub> (°C)</th><th>ΔH<sub>m</sub> (J/g)</th><th>T<sub>f, onset</sub> (°C)</th><th>T<sub>f, 1st</sub> (°C)</th><th>T<sub>f, 2nd</sub> (°C)</th><th>T<sub>f, endset</sub> (°C)</th><th>ΔH<sub>f</sub> (J/g)</th></tr></thead><tbody><tr><td>HD82.44 0 cycles</td><td>–</td><td>16.4</td><td>19.6</td><td>23.9</td><td>193.7</td><td>17.3</td><td>14.2</td><td>6.8</td><td>-3.8</td><td>192.4</td></tr><tr><td>HD82.44 50 cycles</td><td>Top</td><td>16.6</td><td>19.2</td><td>24.8</td><td>196.2</td><td>16.6</td><td>13.7</td><td>5.8</td><td>-5.4</td><td>194.0</td></tr><tr><td>HD82.44 50 cycles</td><td>Middle</td><td>16.6</td><td>19.0</td><td>24.6</td><td>197.6</td><td>16.6</td><td>13.9</td><td>5.9</td><td>-5.3</td><td>193.3</td></tr><tr><td>HD82.44 50 cycles</td><td>Bottom</td><td>16.6</td><td>19.4</td><td>25.0</td><td>196.1</td><td>16.7</td><td>13.5</td><td>5.6</td><td>-5.5</td><td>192.1</td></tr><tr><td>HD82.44200 cycles</td><td>Top</td><td>16.6</td><td>19.1</td><td>24.6</td><td>197.6</td><td>16.7</td><td>13.9</td><td>5.6</td><td>-5.6</td><td>192.6</td></tr><tr><td>HD82.44200 cycles</td><td>Middle</td><td>16.6</td><td>19.1</td><td>25.4</td><td>196.3</td><td>16.8</td><td>13.8</td><td>5.5</td><td>-5.4</td><td>192.6</td></tr><tr><td>HD82.44200 cycles</td><td>Bottom</td><td>16.6</td><td>19.1</td><td>25.3</td><td>197.8</td><td>16.8</td><td>13.7</td><td>5.8</td><td>-5.4</td><td>192.9</td></tr><tr><td>OD82.66 0 cycles</td><td>–</td><td>18.1</td><td>21.4</td><td>32.4</td><td>206.4</td><td>23.1</td><td>15.1</td><td>–</td><td>8.4</td><td>206.4</td></tr><tr><td>OD82.66 50 cycles</td><td>Top</td><td>18.2</td><td>21.4</td><td>32.4</td><td>205.1</td><td>21.9</td><td>13.8</td><td>–</td><td>8.6</td><td>201.4</td></tr><tr><td>OD82.66 50 cycles</td><td>Middle</td><td>18.3</td><td>21.5</td><td>32.4</td><td>204.7</td><td>22.1</td><td>13.8</td><td>–</td><td>8.3</td><td>202.4</td></tr><tr><td>OD82.66 50 cycles</td><td>Bottom</td><td>18.2</td><td>21.5</td><td>32.5</td><td>201.8</td><td>22.5</td><td>13.8</td><td>–</td><td>8.9</td><td>200.7</td></tr><tr><td>OD82.66200 cycles</td><td>Top</td><td>17.9</td><td>21.6</td><td>32.6</td><td>203.6</td><td>22.3</td><td>13.3</td><td>–</td><td>8.5</td><td>201.5</td></tr><tr><td>OD82.66200 cycles</td><td>Middle</td><td>18.3</td><td>21.8</td><td>32.7</td><td>205.1</td><td>22.0</td><td>13.4</td><td>–</td><td>8.2</td><td>203.2</td></tr><tr><td>OD82.66200 cycles</td><td>Bottom</td><td>18.0</td><td>21.4</td><td>32.4</td><td>201.1</td><td>22.4</td><td>13.5</td><td>–</td><td>8.4</td><td>200.8</td></tr></tbody></table>

T<sub>m, onset</sub>: Onset melting temperature; T<sub>m, 1st</sub>: First melting peak temperature; T<sub>m, endset</sub>: Endset melting temperature; ΔH<sub>m</sub>: Melting latent heat; T<sub>f, onset</sub>: Onset freezing temperature; T<sub>f, 1st</sub>: First freezing peak temperature; T<sub>f, 2nd</sub>: Second freezing peak temperature; T<sub>f, endset</sub>: Endset freezing temperature; ΔH<sub>f</sub>: Freezing latent heat.

at 1462 cm⁻¹ [31,32]. HD82.44 and OD82.66 PCM had the same functional groups as 1-dodecanol, and there was no formation of new bonds or bands being absent. This indicated that the binary fatty alcohol eutectic PCM was merely a physical integration, preserving the integrity and properties of both raw materials. This integration was highly beneficial for practical thermal energy storage and building applications.

To verify the stability of this physical integration, thermal cycling tests were conducted. The results showed that HD82.44 and OD82.66 PCMs maintained their initial thermal performance after 50 and 200 cycles, respectively (Figs. 5b, c), with phase transition temperatures and latent heat parameters as shown in Table 4. Additionally, no significant differences in thermal performance were observed among the top, middle, and bottom layers of the PCM. The clear appearance of the liquid PCM heated to 40 °C, with no phase separation (Figs. 5d, e), further confirmed this stability. This indicates that the prepared eutectic PCMs possess excellent structural stability and compatibility, maintaining consistent thermal performance even after repeated thermal cycling. This is crucial for ensuring their long-term reliability in thermal energy storage and building applications.

## 4. Conclusion

This study successfully prepared two binary eutectic HD82.44 and OD82.66 PCMs based on biobased 1-dodecanol, 1-hexadecanol, and 1-octadecanol fatty alcohols through theoretical calculations, binary phase diagram fitting, and experimental validation.

HD82.44 and OD82.66 PCMs exhibited suitable phase change temperatures, high phase change enthalpies, and high specific heat capacities, fully validating their potential for low temperature building thermal management applications. FTIR analysis indicated that HD82.44 and OD82.66 PCMs retained the integrity of the raw materials after mixing, demonstrating that their physical integration is stable and reliable. Combined with the results of thermal cycling tests, these PCMs maintained their initial thermal performance even after 50 and 200 cycles, with no phase separation, highlighting their excellent structural stability and physical compatibility. These characteristics suggest that two binary fatty alcohol eutectic PCMs can effectively enhance building energy efficiency and are feasible for long-term applications.

Although this study has demonstrated the excellent performance of HD82.44 and OD82.66 fatty alcohol eutectic PCMs in experiments, further research is needed to explore their long-term compatibility in actual building environments, especially regarding potential leakage at high temperatures. Therefore, innovative encapsulation techniques will be key to ensuring the stability and efficiency of these materials in practical applications.

In conclusion, this study provides important experimental insights

into the development and application of two fatty alcohol eutectic PCMs, offering a foundation for optimizing and advancing the use of these materials in thermal energy storage for buildings.

### CRediT authorship contribution statement

Dehong Li: Writing – original draft, Methodology, Investigation, Data curation. Thomas Lenfant: Methodology. Véronic Landry: Writing – review & editing. Denis Rodrigue: Writing – review & editing. Alireza Kaboorani: Writing – review & editing. Xiaodong (Alice) Wang: Writing – review & editing, Methodology, Investigation.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Acknowledgments

The authors are grateful to the Natural Sciences and Engineering Research Council of Canada (NSERC) for the financial support, Grant No. CG125664 and GF136078, as well as the China Scholarship Council (No. 202008350164) and the Fonds de recherche du Québec (308460).

### Data availability

The authors do not have permission to share data.

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