Abstract:

Objective Thermal energy storage and thermoregulatory textiles utilizing phase change materials (PCMs) can autonomously regulate micro-environment temperatures through phase transition processes, thereby significantly improving wear comfort and attracting considerable research interest. However, issues such as limited latent heat capacity and constrained regulation duration impede their broader development and application. These limitations are inherently linked to the crystallization behavior of PCMs. In order to address these limitations and further advance the thermal management performance of PCM-based textiles, this work systematically investigates the crystallization kinetics of MXene-incorporated phase-change microcapsules, as MXene exhibits exceptional thermal conductivity that can effectively accelerate thermal response and regulate the crystallization behavior of phase-change materials.

Method The microcapsules were synthesized by emulsion electrostatic spraying techniques, employing n-octadecane as the core, sodium alginate as the wall material, and MXene as an enhancer. The non-isothermal crystallization behavior of microcapsules doped with varying MXene contents was investigated using differential scanning calorimetry (DSC) at distinct cooling rates (Φ=5, 10, 15, 20 ℃/min). Additionally, crystallization kinetics were analyzed by the Jeziorny method, the Mo method, and the Kissinger equation to quantify crystallization mechanisms and activation energy.

Results The DSC results showed that with the increase of Φ, little difference appeared in the initial crystallization temperature of the same microcapsule, but the crystallization peak temperature decreased by 1-2 ℃, the peak width of the crystallization peak becames larger, and the half-crystallization time (t_1/2) decreased significantly, indicating that the crystallization rate increased with the increase of the cooling rate. In MXene-modified microcapsules, the addition of 0-4% MXene increases the crystallization peak temperature. The results indicated that for a given cooling rate Φ, an increase in MXene content led to a situation where half-crystallization time (t_1/2), cooling function (F(T)), and crystallization activation energy initially decreased before subsequently increasing. This suggests that adding MXene would enhance the crystallinity of microcapsules, whereas 5% MXene loading, it began to suppress the crystallization rate. This phenomenon occurred because the confined MXene acted as a nucleation catalyst during the initial microcapsule crystallization, facilitating crystal nucleation and growth on its surface. When the MXene content exceeds 4%, a rigid network would develop within the system, significantly hindering further crystal growth. Notably, microcapsules containing 4% MXene exhibited approximately 30% reduction in t_1/2, a 42% decrease in the average F(T), and about a 28% reduction in activation energy relative to unmodified samples. These findings suggest that MXene mass concentration from 0% to 4% can significantly accelerate non-isothermal crystallization, facilitate nucleation, and lower the energy barrier for crystallization. As a heterogeneous nucleating agent, MXene's two-dimensional lamellar architecture provides nucleation sites, thereby enhancing the crystallization kinetics and thermal properties of the microencapsulated PCMs.

Conclusion Non-isothermal crystallization kinetics demonstrate that, at cooling rates of 5, 10, 15, 20 ℃/min, the optimal dosage of MXene modifiers can effectively decrease the activation energy required for the nucleation and growth of crystalline phases in microcapsules, thereby accelerating their crystallization kinetics. Consequently, analyzing the non-isothermal crystallization behavior offers valuable insights into optimizing the crystallization properties of phase change microcapsules, which can enhance their thermal storage capacity and thermoregulatory performance. This research provides useful reference for the development of high-efficiency thermoregulating and heat-storage textiles.

Key words: composite phase change microcapsule, n-octadecane, sodium alginate, MXene, non-isothermal crystallization, crystallization activation energy, thermal energy storage and temperature regulation textiles