Integration of efficient photothermal and flexible solid-solid PCM for personal thermoregulation in cold environments

Summary

Personal thermal management (PTM) technology demonstrates extensive development prospects in the domains of energy, environment, and medicine. Nevertheless, it still suffers from drawbacks such as high costs and restricted environmental adaptability. The integration of phase change materials (PCMs) and photothermal conversion technologies holds the potential to address these issues. In this study, an efficient photothermal and flexible solid-solid phase change composite was successfully fabricated. This composite exhibits excellent processing and molding performance, and it remains free of liquid leakage at elevated temperatures. It exhibits high thermal conductivity (2.9 W m⁻¹ K⁻¹) and a high phase transition enthalpy (184 kJ/kg), and the absorptivity exceeds 90%. The phase change composite is capable of performing efficient photothermal phase change heat storage in extreme cold environments (such as at Zhongshan Station in Antarctica) and maintaining a temperature above 16°C for 8 h, thereby demonstrating significant application potential in wearable thermal management garments for personal thermoregulation.

Graphical abstract

Highlights

• •It exhibits high thermal conductivity (2.9 W m⁻¹ K⁻¹) and high enthalpy value (184 J/g)
• •The sample exhibits both flexible and solid-solid phase change performance
• •The absorptivity exceeds 90% within the spectral range of 0.25–2.5 μm
• •It maintains a temperature above 16°C for 8 h in cold environments

Physics; Photon absorption; Applied sciences

Introduction

Thirty-five years ago, the president of Frisby Company conceptualized the development of phase change materials (PCMs) for application in wearable apparel to store body heat.^1,2,3 Initially deployed in personal thermal management for the space industry, PCMs ensured the regulation of astronauts’ body temperature in extraterrestrial environments through heat conversion and exchange mechanisms. In recent years, the global PCMs market has experienced robust growth. Industry data indicate that the market size reached approximately US$4.77 billion in 2020 and is projected to surpass US$10 billion by 2025.^4,5 The Asia-Pacific region accounts for over 40% of this growth trajectory, with China alone comprising more than 60% of the PCMs applications in building energy efficiency and new energy sectors.⁶ With advancing technological integration and scenario-specific refinement, PCMs are anticipated to achieve a more optimized equilibrium between comfort and functionality across diverse domains, including healthcare, aerospace, and specialized operations.^7,8,9,10,11

The integration of PCMs with photothermal conversion technology enables not only the efficient storage of thermal energy derived from photothermal conversion but also the regulation of temperature during heat storage and release,^12,13 thereby achieving the integrated functionality of solar energy absorption-thermal energy conversion-energy storage regulation. When applied to textiles for the fabrication of composite phase change fabrics, this technology enables rapid light-responsive behavior, converting light energy into storable thermal energy while maintaining the internal temperature of the fabric within a specified range to meet users’ thermal comfort requirements.^14,15,16 However, the limited thermal conductivity and leakage issues inherent in solid-liquid PCMs have constrained their broad-scale adoption. In response, scientists have undertaken a series of composite modification studies on these materials in recent years, thereby advancing the development of integrated photothermal conversion and phase change heat storage technologies. 3D printed phase change composite can overcome shape limitations and optimize structures to construct complex object designs for effective thermal management.¹⁷ Prabhu et al.¹⁸ found that the paraffin-based PCM cooling method can cope with a greater drop in the temperature of solar photovoltaic modules from 3°C to 26.6°C, thereby stimulating a 1%–56% increase in the electrical efficiency of the modules. Moreover, Shi et al.^19,20 proposed a new concept of supercooled spatiotemporal PCM, achieving long-term storage and intelligent release of latent heat, which inspired the design of advanced solar thermal fuels. Nevertheless, PCM material still suffers from drawbacks such as low thermal conductivity and liquid leakage at elevated temperatures. In this research, paraffin was infiltrated into a cross-linked network of polyolefin elastomer (POE) elastomer and compounded with reduced graphene oxide (rGO) to fabricate the phase change composite, it exhibits high thermal conductivity (2.9 W·m-1·K-1) and a high phase transition enthalpy (184 kJ/kg), the absorptivity exceeds 90%. This phase change composite possesses excellent processing and molding properties, and it remains free of liquid leakage at elevated temperatures. After coating with insulating silica aerogel, the bulk phase change composite (with dimensions of 10 × 10 × 1.5 cm) can perform efficient photothermal phase change heat storage in extreme cold environments (Zhongshan Station in Antarctica); it maintains a temperature above 16°C for 8 h,. thereby demonstrating significant application potential in wearable thermal management garments for personal thermoregulation.

Results and discussions

Experimental measurements

Figure 1A shows schematic diagram for forming the photothermal phase change composite material. To enhance the anti-leakage property of PCMs and endow them with excellent cyclic stability, the cross-linked POE network serves as a flexible three-dimensional skeleton. PCMs are introduced into this flexible framework. The composite is further integrated with high thermal conductivity and photothermal-effect rGO. This design endows the material with efficient photothermal phase change thermal storage performance, achieving synergistic enhancement of leakage resistance, cyclic durability, and thermal management capabilities. Briefly, 50 g of POE was processed in an internal mixer at 150°C for 5 min. Subsequently, 0.35 g of dicumyl peroxide (DCP,as the crosslinking agent) was added, followed by an additional 5 min of processing to obtain a cross-linked POE network. The cross-linked POE was mixed and stirred with a suitable amount of molten PCM at 80°C for 4 h, after which rGO was introduced and the mixture was continuously stirred for another 4 h. Upon cooling, the phase change composite material was obtained. The composite exhibits outstanding processing and forming properties, enabling it to be fabricated into predefined shapes and sizes via mold pressing. Upon coating with insulating silica aerogel, the bulk phase change composite demonstrates efficient photothermal phase change thermal storage capability in extremely cold environments, as illustrated in Figure 1B. Even in extreme environments such as China’s Zhongshan Station in Antarctica, the phase change composite demonstrates efficient photothermal conversion via rGO, absorbing solar radiation energy and storing it within the PCM matrix. During practical application, the thermal energy stored in PCM is released to maintain personal temperature, enabling round-the-clock (day/night) thermoregulatory operation.

Figure 1.

Preparation of photothermal phase change composite material for personal thermoregulation in cold environments

(A) Schematic of the fabrication process of the photothermal phase change composite material.

(B) Working schema when wearing the photothermal phase change composite material to achieve personal thermoregulation in a cycle between absorbing heat (in sunlight) and release heat (in dark) as demanded.

rGO, owing to its inherent high thermal conductivity²¹ and photothermal effect(97.6%),²² can significantly enhance the photothermal conversion and thermal energy storage efficiency of matrix materials when composited with PCMs. Given that the quality of rGO nanosheets directly influences the performance of phase change composite, characterization studies were conducted to analyze the morphology and structure of rGO nanosheets (Figures 2A and 2B). The lateral dimension of rGO nanosheets is approximately 10 μm. Under transmission electron microscopy, it exhibits distinct boundaries and high transparency, suggesting that the rGO layers are relatively thin. Atomic force microscopy characterization revealed that the thickness of rGO nanosheets ranges from approximately 5 to 8 nm, corresponding to 6 to 10 layers.

Figure 2.

Performance of photothermal phase change composite material

(A) SEM image of rGO; the inset shows the TEM morphology of rGO.

(B) AFM image of rGO.

(C) Latent heat and thermal conductivity of POE/PCM and rGO composites in different proportions.

(D) DSC curve of phase change composite (the mass ratio of rGO: POE: PCM is 10: 5: 85 wt %); inset shows the photo of phase change composite.

(E) The cyclic stability test for latent heat of the rGO/POE/PCM; inset shows the IR images of pure PCM and rGO/POE/PCM at elevated temperatures.

(F) A comparison of the latent heat of this work and previously reported solid-solid phase change materials.^{13,23,24,25,26}

Subsequently, high-quality rGO nanosheets were incorporated into PCMs, and the composites were characterized by thermal conductivity and latent heat at varying mass ratios (Figure 2C). The thermal conductivity of the phase change composite increased from 0.3 W m⁻¹ K⁻¹ (0 wt % of rGO) to 6.7 W m⁻¹ K⁻¹ (20 wt % of rGO), whereas its latent heat capacity decreased monotonically with increasing rGO content. Considering the trade-off between thermal conductivity and latent heat storage capacity, the composite with 10 wt % rGO was selected as the optimal sample, it exhibits high thermal conductivity (2.9 W m⁻¹ K⁻¹) and a high phase transition enthalpy (184 kJ/kg). Figure 2D displays the photo and differential scanning calorimetry curve of phase change composite. During the heating process, the phase change composite began to exhibit endothermic phase transition behavior at 24.3°C and continued until 36.5°C, with a peak transition temperature of 29.0°C. This broad phase transition temperature range aligns well with the personal thermoregulation needs, indicating its potential for applications in personal thermal management. As shown in the physical image, the phase change composite material appears as a black powder and can be fabricated into desired shapes and sizes via compression molding.

The phase change composite exhibits favorable cyclic stability (Figure 2E), with its phase change enthalpy remaining at 95% after 100 cycles. Meanwhile, in contrast to pure PCM, the phase change composites belong to the solid-solid phase change type. When exposed to conditions above the phase change temperature, no liquid leakage is observed, and the sample maintains its original shape. A comparison of the enthalpy values of the solid-solid phase change material (SSPCM) developed in this study and previously reported SSPCMs is provided in Figure 2F. It is worth emphasizing that the SSPCM synthesized in this work possesses a relatively high phase change enthalpy.

Photothermal measurements

Phase change composite synthesized via chemical processes may contain residual reagents, which preclude their direct contact with human skin. To address this issue, the phase change composite block was encapsulated within a linear low-density polyethylene (LLDPE) film. In this work, LLDPE with a thickness of 10 μm was selected for its excellent tensile strength and puncture resistance (Figure 3A). The physical parameters of LLDPE are shown in Table 1. Linear LLDPE demonstrates a high transmittance exceeding 93% across the entire near-ultraviolet and visible spectral ranges (280–800 nm), suggesting that the LLDPE thin layer has negligible impact on the photothermal effect of phase change composite.

Figure 3.

The absorption performance of phase change composite

(A) Transmissivity of LLDPE; inset shows the tensile and puncture resistance of LLDPE.

(B) Absorptivity of PCM, phase change composite, and phase change composite@LDPE.

(C) Flexible property characterization of the phase change composite.

(D) Wearable performance demonstration of phase change composite and infrared imaging of the heat release in low-temperature environments.

Table 1.

The physical parameters of materials

Sample	Density (kg·m−3)	Thermal conductivity (W·m−1·K−1)	Specific heat (J·kg−1·K−1)
LLDPE	910	0.32	1,900
Silica nano-aerogel	180	0.02	745
PCM composite	950	2.9	2,000

The absorptivity of various samples in the AM1.5G solar spectral band (0.25–2.5 μm) was measured using a ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer . As shown in Figure 3B, the UV-vis-NIR absorption spectra reveals that the PCM composites integrated with rGO nanosheets exhibit significantly enhanced solar absorptivity in comparison to pure PCM. Specifically, within the visible spectrum (0.4–0.76 μm), the average solar absorptivity of the composite reaches up to 93%, which is approximately 30% higher than that of pure PCM. This improvement in solar-thermal conversion performance is ascribed to the broad-spectrum absorption capability of rGO nanosheets. Notably, even after encapsulation with an ultrathin transparent linear LLDPE film, the final composite maintains a broadband solar absorptivity exceeding 90%. This result demonstrates the composite’s efficient utilization of solar energy and underscores its promising potential for effective heating under solar radiation.

The phase change composite exhibits high flexibility (Figures 3C and Video S1) and can be readily bent and twisted. Additionally, large-area phase change composites enable the realization of wearable applications and personal thermal management (Figure 3D). Upon absorbing photothermal energy, the phase change composite can release heat at low temperatures, thereby providing thermal support to personal thermoregulation.

Application in cold environment

The solar energy absorption - thermal energy conversion - energy storage regulation performance of phase change composite was validated through field measurements in an actual environment (Hangzhou, Zhejiang, China, June 3–4, 2024, Figure 4A). Temperature variations of phase change composite were monitored in real time using thermocouples (PT 100), while local surface radiation intensity was recorded at 1-min intervals via a solar radiation power meter (Xinbao, SM206). Between 09:00 and 11:30 h, the terrestrial solar irradiance exhibits a gradual increase from 450 to 730 W/m². During this period, the phase change composite absorbs sufficient solar radiation energy to initiate phase transition and accomplish thermal energy storage. The phase change composite temperature rises from the initial ambient temperature (25°C) to 36°C, evidencing complete phase change energy storage. The subsequent temperature elevation of phase change composite is attributed to the exceptional photothermal conversion efficiency of rGO, which enables continuous heat accumulation. Thereafter, the PCM is encapsulated with light-shielding box, and its heat release and thermal insulation properties are recorded. Starting at 14:30, the phase change composite temperature decreases to 36°C and initiates phase change-induced heat release for thermal insulation, a process lasting 36 h. This prolonged performance demonstrates the material’s superior heat release insulation capacity, primarily attributable to the high latent heat of phase change inherent in PCM.

Figure 4.

The personal thermoregulation performance of phase change composite in cold environments

(A) Heat absorption and release characteristics of phase change composite blocks under actual sunlight irradiation.

(B) Temperature and solar radiation intensity at Zhongshan Station in Antarctica in January 2024.

(C) Energy consumption and supply demand of the personnel in cold environments.

(D) Heat absorption and release characteristics of phase change composite blocks under cold environments.

Additionally, an investigation is required into the solar energy absorption and personal thermoregulation performance of PCMs composite in cold environments. To this end, publicly available climatic data from Zhongshan Station in Antarctica (Figure 4B) were selected as reference. In January 2024, Zhongshan Station experienced polar day conditions, with a daily average temperature of −1°C. Notably, solar radiation intensity between 07:00 and 16:00 h exceeded 500 W/m², indicating significant potential for efficient solar energy absorption and phase change thermal energy storage by phase change composite. Through quantitative analysis, the energy replenishment requirements for the personnel in cold environments were determined (Figure 4C), enabling the calculation of the actual PCM material dosage. Taking an adult male (170 cm height, 60 kg body mass, the surface area is 1.65 m²) as a model subject, the surface temperature of the personal is 33°C, the analysis was conducted under −1°C environmental conditions. Considering that the personal metabolic rate increases by a factor of approximately 1.15 in cold environments, so

$$P_{Metabolism}=65\sim 70W/A^2$$ (Equation 1)

where A is the surface area of the human body.

$$P_{Metabolism}=70\times 1.65\times 1.15=133W$$ (Equation 2)

$$P_{Radiation}=A\Delta j\ast =A\delta \left(T_1^4-T_0^4\right)$$ (Equation 3)

$$\Delta j\ast =\epsilon \delta T^4$$ (Equation 4)

where A, δ, T, and ε are the surface area, Stefan Boltzmann constant, thermodynamic temperature, and radiation coefficient, respectively. The ε of silica aerogel gel is 0.38

$$P_{Radiation}=0.38\times 1.65\times 5.67\times \left({\mathrm{3.6.15}}^4-{272.15}^4\right)\times {10}^{-8}=117W$$ (Equation 5)

$$P_{Convection}={\left(T_{body}-T_{cloth}\right)/R_{\begin{array}{c}\underset{=}{cloth}\end{array}}h}_{cloth}A(\left(T_{cloth}-T_{env}\right)$$ (Equation 6)

where h_cloth and R_cloth are the natural convection coefficient of air on the cloth and thermal resistance of cloth. The typical thermal resistance of warm clothing is 0.31 m² K/W.²⁷

$$h_{cloth}=h_0\eta$$ (Equation 7)

where h₀ is convective heat transfer coefficient of the exposed human body²⁸ and η is the correction coefficient, with typical values of 0.4 and 0.6, respectively.

$$h_0=1.48\Delta T^4=3.5W/\left(m^2·K\right)$$ (Equation 8)

$$P_{Convection}\approx 1.75\times 1.65\times 10.8=31W$$ (Equation 9)

$$P_{Breath}=0.0173P_{Breath}\left(5.87-\phi \rho \right)$$ (Equation 10)

where φ and ρ are air humidity and saturated water vapor partial pressure, respectively.²⁹ It is approximately considered as zero under severe cold conditions.

$$P_{Breath}=0.0173\times 133\times 5.87=13.5W$$ (Equation 11)

Based on the foregoing calculations, an additional external heat input of 28.5 W is required for personal thermoregulation to maintain physiological safety in polar cold environments (Zhongshan Station, Antarctica). Therefore, upon absorbing solar radiation and completing phase change energy storage, 5 kg of phase change composite can satisfy the thermal replenishment requirements of personnel for a duration of 10 h.

Furthermore, we simulated the climatic environment of Zhongshan Station and characterized the solar energy absorption, phase change energy storage, and thermal insulation performance of phase change composite. A benchtop cryogenic chamber (Alpicool-C15) was employed to maintain a controlled −1°C cold environment, while a calibrated solar simulator (HF-GHX-XE-300) was used to generate matched solar radiation intensity. The PCM was encapsulated in a silica aerogel layer to reduce thermal loss, with one surface sealed by a transparent LLDPE film to facilitate solar radiation absorption (Figure 4D). At 07:00, the phase change composite was subjected to solar irradiation for heat absorption, with its temperature gradually increasing from the initial −1°C–25°C, marking the onset of endothermic phase change energy storage. Following 5.5 h of continuous solar irradiation, the phase change composite temperature reached 36°C, indicating complete phase change heat storage. The temperature subsequently stabilized at 39°C, resulting from thermal equilibrium between solar energy input and heat dissipation to the cold environment. Thereafter, the solar simulator was switched off, and the phase change composite was encapsulated in silica aerogel to characterize its heat release and thermal insulation performance. In a −1°C cold environment, the phase change composite maintained its temperature above 16°C for 8 h, with the phase change heat release process lasting 7 h. These results demonstrate the phase change composite’s excellent solar radiation absorption and heat release insulation capabilities, highlighting its substantial application potential in personal thermal management for cold environments.

In summary, we demonstrated an efficient photothermal and flexible solid-solid phase change composite for personal thermoregulation in cold environments. Paraffin was infiltrated into a cross-linked network of POE and compounded with rGO to fabricate the phase change composite, it possesses excellent processing properties and remains free of liquid leakage at elevated temperatures. The phase change composite shows high thermal conductivity (2.9 W m⁻¹ K⁻¹), high phase transition enthalpy (184 kJ/kg), and the absorptivity exceeds 90%. Following the coating of its surface with insulating silica aerogel, the bulk phase change composite can perform efficient photothermal phase change heat storage in extreme cold environments and maintaining a temperature above 16°C for 8 h. It demonstrates the enormous potential of wearable thermal management clothing in personal thermoregulation.

Limitations of the study

This study has verified, through experiments and simulated cold environments, the capability of rGO/POE/PCM composite for photothermal absorption and personal thermoregulation, with potential applications in cold environments such as Zhongshan Station, Antarctica. However, no field tests have been conducted in this specific location, nor have other variable climatic conditions in the region been considered. In the follow-up study, it is proposed to conduct on-site tests and verification in cold environments.

Resource availability

Lead contact

Further information and requests for resources and reagents should be directed to and will be fulfilled by the lead contact, Peijia Bai (peijiabai@163.com).

Materials availability

This study did not generate new unique reagents.

Data and code availability

• •Data reported in this article will be shared by the lead contact on request.
• •This paper does not report original codes.
• •Any additional information required to reanalyze the data reported in this paper is available from the lead contact upon request.

Acknowledgments

This work is supported by the Zhejiang Province Postdoctoral Research Subsidy Fund (BSH00001020) and Zhejiang Province Postdoctoral Research Project Selective Funding (ZJ2025181).

Author contributions

P.B. and S.Y. conceived the idea and designed the experiment. Q.Y. prepared and tested the microscopic morphology of the phase change composite. P.B. and Q.Y. organized the data and wrote the manuscript, and all authors reviewed and commented on the manuscript.

Declaration of interests

The authors declare no competing interests.

STAR★Methods

Key resources table

REAGENT or RESOURCE	SOURCE	IDENTIFIER
Chemicals, peptides and recombinant proteins
Phase change materials	SEDIN ENGINEERING CO., LTD. China	CAS no.8002-74-2
POE	Dow Inc. of the United States, NO: 8842	CAS no.63148-62-9
DCP	Nanjing Chemical Reagent Co., LTD	CAS no.80-43-3
rGO	SUZHOU TANFENG CO., LTD. China	CAS no.1034343-98-0
LLDPE	YUJING SUHUA CO., LTD. China	CAS no.9002-88-4
Silica nano-aerogel	SUZHOU TANFENG CO., LTD. China	CAS no. 112926-00-8
Software and algorithms
Origin 2018	Origin Lab	N/A

Method details

Synthesis of rGO/POE/PCM

First, 50 g of polyolefin elastomer (POE, Dow Inc. of the United States, NO: 8842) was subjected to treatment in a mixer for 5 min, with the temperature strictly maintained at 150°C. Subsequently, 0.35 g of Dipropylene glycol peroxide (DCP, Nanjing Chemical Reagent Co., LTD) was added, and the treatment process was continued for an additional 5 min to yield the crosslinked POE network. The crosslinked POE was then mixed and stirred with molten paraffin phase change material (PCM, SEDIN ENGINEERING Co., LTD) at 80°C for a duration of 4 h. Reduced Graphene Oxide (rGO) were subsequently incorporated, with the mass ratio of rGO: POE: PCM specified as 10: 10: 80 wt %. Finally, after a cooling procedure, the rGO/POE/PCM was successfully prepared. The bulk phase change composite (10 × 10 × 1.5 cm) was prepared through a pressurized module.

Characterizations and measurements

The morphological features of the ceramic powder and multilayer ceramic samples were examined by scanning electron microscopy (SEM). The SEM observations were performed using a Hitachi TM-1000 scanning electron microscope (Hitachi, Japan). The DSC curve of the composite was scanned using a differential scanning calorimeter (Diamond DSC, PerkinElmer instruments) to obtain the function of specific heat with function of temperature. The experiment was conducted at a heating rate of 10°C/min, the calorimetric accuracy of this DSC system is less than 0.1%, and the temperature accuracy is within ±0.01°C. The absorption spectra were performed using a UV-Vis-NIR spectrophotometer (Shimadzu, PE lambda 750) with an integrating sphere (Agilent, Cary 5000) and a Fourier transform infrared spectrometer with an integrating sphere (PerkinElmer, Frontier Optica) (PIKE). Measurement by MCT mid-infrared integrating sphere.

Quantification and statistical analysis

There are no quantifications or statistical analyses to include in this study.

Published: November 17, 2025