Photothermal Phase Research Articles

One-Step Synthesis of Multifunctional Bacterial Cellulose Film-Based Phase Change Materials with Cross-Linked Network Structure for Solar-Thermal Energy Conversion, Storage, and Utilization.

As one of the important directions of solar energy utilization, the construction of composite photothermal phase change materials (PCM) with reasonable network support and low leakage in the simple method is important to solve the transient availability of solar energy and achieve long-lasting energy output. Here, a multifunctional silylated bacterial cellulose (BC)/hydroxylated carbon nanotube (HCNT)/polyethylene glycol (PEG) (SBTP) photothermal film-based PCM with cross-linked network structure is prepared by simple one-step synthesis. The formation of the cross-linked network structure achieves the enhancement of BC support network, prominent dispersion of HCNT and the direct introduction and perfect interlocking of PEG. Therefore, the optimal SBTP film exhibits high thermal enthalpy of 145.1Jg-1, enthalpy efficiency of over 94%, robust shape stability and low leakage of <1.2%. It also displays high photothermal conversion of over 80°C, photothermal storage of 394 sg-1 and excellent stability. Thus, it can demonstrate a maximum output voltage of 423mV and high power density of 30.26Wm-2 under three solar irradiations when applied in the solar-thermal-electric energy conversion field. Meanwhile, it also can apply in the thermal management of solar cell and light-emitting diode (LED) chip, and convert the waste heat into electricity, demonstrating multi-scene application capability.

Intrinsic photothermal phase change materials with enhanced toughness and flexibility for thermal management in extreme environments

Polymeric solid–solid phase-change materials (SSPCMs) are capable of reversibly absorbing or releasing high latent heat and have been widely studied for thermal energy storage (TES) due to their excellent shape stability and certain mechanical properties. The photothermal fillers were introduced to impart SSPCMs with photo-responsive ability. However, the incompatibility interface between fillers and SSPCMs matrix always causes serious deterioration of mechanical toughness and flexibility. Herein, we report an intrinsic photothermal SSPCM by incorporating a reactive photothermal agent (dihydroxy naphthalene (DN)) into linear polyurethane SSPCMs. The prepared SSPCMs have adjustable phase transition enthalpy and temperature as well as long-term cycle stability. The highest efficiency of SSPCM in near-infrared photothermal conversion including sensible and latent heat is 59.7 %, and the solar photothermal conversion efficiency is 48.1 %. Moreover, SSPCMs exhibit superior mechanical toughness of 193 MJ/m3 and flexibility, which can withstand repeated rotation, folding and stretching. The SSPCMs developed in this work can enable the human body to obtain the heat needed for life through photothermal conversion in extreme environments such as the Arctic, increasing the probability of survival. Therefore, this study provides a facile strategy for fabricating intrinsic photothermal SSPCMs with high toughness and flexibility properties, which have great potential in wearable device for thermal management in extreme environments.

Photothermal materials with energy-storage properties provide an energy-saving design for highly efficient anti-icing/deicing applications

All-weather, high-efficiency solar photothermal anti-icing/deicing systems are of great importance for solving the problem of ice accumulation on outdoor equipment surfaces. In this study, a photothermal phase change material with a micro-porous structure (MP@PPCM) is prepared via salt-template and melt-blending methods. Owing to the synergistic effect of the latent heat released from the phase change material and the thermal-insulation effect of the internal micro-porous structure, MP@PPCM exhibits a low cooling rate and a high equilibrium temperature during the cooling process. In addition, MP@PPCM exhibits excellent photothermal conversion performance under light illumination, providing the basis for highly efficient anti-icing/deicing. Notably, the single droplet icing and melting results show that the droplet has the longest icing delay time and the shortest melting time on the MP@PPCM sample compared to that on the other samples analyzed. Furthermore, day–night alternation, multiple freezing–melting, and chemical stability tests verify the outdoor applications potential of MP@PPCM. The study results provide a way to prepare high-efficiency photothermal anti-icing/deicing materials in the absence of light conditions.

Wood Lamella-Inspired Photothermal Stearic Acid-Eutectic Gallium-Indium-Based Phase Change Aerogel for Thermal Management and Infrared Stealth.

Eutectic Gallium-Indium (EGaIn) liquid metalis an emerging phase change metal material, but its low phase transition enthalpy and low light absorption limit its application in photothermal phase change energy storage materials (PCMs) field. Here, based on the dipole layer mechanism, stearic acid (STA)-EGaIn-based PCMs which exhibit extraordinary solar-thermal performance and phase change enthalpy are fabricated by ball milling method. The wood lamella-inspired cellulose-derived aerogel and molybdenum disulfide (MoS2 ) are used to support the PCMs by the capillary force and decrease the interfacial thermal resistance. The resulted PCMs achieved excellent photothermal conversion performance and leakage proof. They have excellentthermal conductivity of 0.31W m-1 K-1 (this is increased by 138% as compared with pure STA), and high phase change enthalpy of187.50 J g-1 , which is higher than the most of the reported PCMs. Additionally, the thermal management system and infrared stealth materials based on the PCMs are developed. This work provides a new way to fabricate smart EGaIn-based PCMs for energy storage device thermal management and infrared stealth.

Highly stretchable phase change composites for simultaneous health monitoring and thermotherapy

Multifunctional wearable smart devices for personal health management are currently gaining widespread attention. However, precise monitoring and efficient treatment of muscle injuries with multifunctional wearable smart devices still face significant challenges. In this work, stretchable phase change composites (SPCCs) with dual-functional layers are developed by integrating a photothermal phase change layer with an electrothermal conductive layer, where the phase change and conductive layers are constructed by confining island-like MXene-enhanced phase change particles and dispersing multiwalled carbon nanotubes (MWCNTs) in a continuous elastic supporting network, respectively. The resulted SPCCs exhibit excellent flexibility with an elongation at break of 334% and realize sensing performance and efficient photo-/electro-thermal energy conversion. These enticing properties enable SPCCs to simultaneously monitor the motions of human body and implement thermal therapy for the rapid recovery of muscle injury in SD rats, offering possible guidance for the rational designs of next-generation wearable electronic devices for individual health management.

Parameter optimization of hollow-core optical fiber phase modulators.

We studied the effect of varying gas concentration, buffer gas, length, and type of fibers on the performance of optical fiber photothermal phase modulators based on C2H2-filled hollow-core fibers. For the same control power level, the phase modulator with Ar as the buffer gas achieves the largest phase modulation. For a fixed length of hollow-core fiber, there exists an optimal C2H2 concentration that achieves the largest phase modulation. With a 23-cm-long anti-resonant hollow-core fiber filled with 12.5% C2H2 balanced with Ar, phase modulation of π-rad at 100 kHz is achieved with a control power of 200 mW. The modulation bandwidth of the phase modulator is 150 kHz. The modulation bandwidth is extended to ∼1.1 MHz with a photonic bandgap hollow-core fiber of the same length filled with the same gas mixture. The measured rise and fall time of the photonic bandgap hollow-core fiber phase modulator are 0.57 µs and 0.55 µs, respectively.

Reprocessable, Photothermal Phase Change Material-Based Hybrid Polymeric Networks for Solar-to-Thermal Energy Storage

Polymeric photothermal phase change material composite (PPCMC) networks with excellent reprocessability, high latent heat, and intrinsic network stability have the great advantages of solar energy storage and conservation and environmental protection resulting from the covalent crosslinking network structure and long-life inorganic photothermal agents. Herein, the reprocessable PPCMCs were successfully prepared by introducing the reactive diisocyanate-terminated poly(ethylene glycol) (PEG) and multiple amino-functionalized carbon black (CB)that serve as the phase change component and the photothermal curing agent, respectively. The phase change properties, mechanical strength, and photothermal efficiency of PPCMCs can be tuned by the chain length of PEG and the loading content of CB and the catalyst. PPCMCs possess the largest latent heat of 126.7 J/g, the highest photothermal conversion efficiency of 89.0%, superior shape stability even at 140 °C, high thermal stability beyond 300 °C, and reprocessing ability by introducing the catalyst of the transcarbamoylation reaction. Also, the PPCMCs exhibit high thermal reliability after accelerated thermal cycling and reprocessing, featuring nearly consistent chemical and crystalline structures, latent heat, phase change temperature, and photothermal properties. This synthetic strategy provides an alternative to obtain multi-functional PPCMCs due to the enhanced interfacial interaction between inorganic particles and the polymer matrix via covalent linkages.

Precise Preparation of a Multilayer Tubular Cell Sheet with Well-Aligned Cells in Different Layers to Simulate Native Arteries

Compared with artificial vascular grafts, bottom-up tubular cell sheets (TCSs) without scaffolds have shown promise for patients with cardiovascular disease. However, TCS therapy also faces the challenges of lengthy maturation time, elaborate operation, and weak mechanical strength. In this work, a structured small-diameter vascular graft (SDVG), consisting of three layers of TCSs, with different cell types and arrangements, was fabricated using layer-by-layer assembly of naturally formed TCSs and further cell culture. To this end, a surface-patterned collagen-coated cylindrical substrate was designed for the efficient harvesting of naturally formed and well-aligned TCSs. The patterned collagen (type I) layer facilitated the adhesion and orientation of cells, and a continuous tubular cell monolayer was naturally formed after approximately 4 days in cell culture. Biocompatible near-infrared (NIR) light was used to trigger the photothermal phase transition of the collagen coated on the cylindrical substrate to dissociate the collagen layer. As a result, an intact TCS could be harvested within a few minutes. These naturally formed and well-aligned TCSs exhibited outstanding free-standing performance without rugosity, facilitating their operability and practical application. A ring tensile test showed that orientation was critical for improving the mechanical properties of TCSs. The layer-by-layer assembly of SDVGs not only is easy to manipulate and has a short preparation time but also overcomes the bottleneck of forming a hierarchically structured vascular graft. This approach shows promise for repairing damaged blood vessels.

Synthesized acrylate monomers to improve photothermal conversion efficiency and fire safety of PEG/black phosphorus (BP) phase change composites

The combination of photothermal components and phase change materials (PCMs) has received extensive attention. However, the incorporation of photothermal functionality into PCMs confronts the fatal problems of low utilization efficiency and performance compromise during processing. In this work, an acrylate monomer-passivation strategy was proposed to wrap photosensitive black phosphorus nanosheets (CG-BPs) to retain their intrinsic properties for high photothermal conversion efficiency. In addition, a flame-retardant acrylate (MCBDB) was further synthesized to crosslink with CG-BPs and build a framework for PEG1000 encapsulation. The resulting composite (cPCMs-1.2) was able to achieve a photothermal conversion efficiency of 85.3% even with a low content of CG-BPs (1.2 wt%) and unconcentrated irradiation. And benefiting from the synergistic flame-retardancy of CG-BPs and poly(MCBDB), the PCM composites displayed a reduced peak heat release rate of 38.7% compared with that of pristine PEG1000, indicating improved fire resistance. Considering its appropriate phase-change temperature, the application demonstration of the fabricated cPCMs-1.2 for human body hot compress was conducted, in which the promoting effect on blood circulation was observed. This work provides us with a new idea for the simple fabrication and new application of photothermal PCM with high photothermal conversion efficiency and application safety.

Thermally induced flexible phase change hydrogels for solar thermal storage and human thermal management

Hydrated salt is widely used for solar energy utilization and thermal management due to its phase change properties. However, its practical application is limited by issues such as leakage, phase separation, and supercooling, which require urgent attention. To address these challenges, a novel approach was proposed by synthesizing a photothermal phase change hydrogel using sodium acetate trihydrate as the phase change material, graphene oxide as the photothermal agent, and acrylamide and konjac glucomannan as the support structure. The hydrogel's three-dimensional network effectively reduces the likelihood of salt leakage and suppresses supercooling to a range of 1.2–3.1℃. The photothermal conversion efficiency of the phase change hydrogel can reach 89.7% due to high light absorption performance of graphene oxide. Hydrogels with phase change properties have an energy storage density of 179.2 J/g. As hydrated salts undergo a solid–liquid transition, phase change hydrogels experience a dramatic change in stiffness due to the temperature shift. Due to the existence of a three-dimensional network structure, a continuous and effective heat transfer path is formed inside the hydrogel, which presents thermal conductivity of 0.868 W/(m·k). The unique properties of phase change hydrogels pave a new avenue for personal thermal management and solar energy utilization.

Photothermal Effect and Phase Transition in VO2 Enhanced by Plasmonic Particles

Phase change metasurfaces based on VO2, which are pre-heated with electric current and optically addressed by projected structured light hologram, are considered to become a new paradigm in programmed THz/middle IR flat optics. Macroscopic quasi-homogeneous arrays of Au nanoparticles show large near IR absorption and a significant photothermal effect capable of boosting a light-triggered switching of VO2 and are to be carefully examined. We propose a new approach to simultaneously probe the altered temperature and electric conductivity of a hybrid Au particle-VO2 film composite by monitoring a phase shift and attenuating a surface acoustic wave in a YX128° cut LiNbO3 substrate. The method shows a temperature resolution of 0.1 °C comparable with the best existing techniques for studying nanoobjects and surfaces. The laser-induced photothermal effects were characterized in a macroscopic array of Au nanostars (AuNSts) with different surface coverage. In a monolayer of 10 nm Au, coupled plasmonic nanoparticles were deposited on the LiNbO3 substrate. An optically triggered insulator-metal transition assisted by photothermal effect in AuNSts/VO2/TiO2/LiNbO3 composites was studied at varied light power. We believe that the proposed SAW-based method is of significant importance for the characterization and optimization of radiation absorbing or/and electrically heated elements of metasurfaces and other devices for lab-on-chip and optical communication/processor technology.

Dispersion turning point-enhanced photothermal interferometry gas sensor with an optical microfiber interferometer

Photothermal interferometry (PTI) spectroscopy is a background-free and ultrasensitive gas or chemical sensing method. To date, most works have focused on applying different techniques to improve the sensitivity of PTI gas sensors via enhancing the photothermal (PT) phase modulation. Herein, we develop an all-fiber dispersion turning point (DTP)-enhanced PTI gas sensor with a taper-based mode interferometer in which the PT phase detection sensitivity of the interferometer is enhanced in a millimeter-long single fiber PTI configuration, which has not been studied yet. The design is demonstrated by conducting the measurement of acetylene with a 3-mm-long, 2.29-μm-diamter microfiber interferometer. A lower detection limit of 965 parts per billion (ppb) acetylene is achieved when the probe wavelength is operating near DTP, showing 16 times enhancement. Besides, theoretical analysis shows that the sensitivity of phase detection would be enormously enhanced when the dispersion factor approaching zero. By optimal design of the taper-based mode interferometer, together with thinner fiber diameter and longer fiber length, gas detection may be further improved by double enhancement of both PT phase generation and phase detection. With advantages of high sensitivity, compact size and low cost, the proposed all-fiber DTP-enhanced PTI gas sensor is potentially promising for ultra-sensitive trace chemical or biochemical sensing.

Amplified Photothermal Phase Modulation for Carbon Dioxide Detection by Operating a Dual-Mode Interferometer at Destructive Interference.

Photothermal interferometry is a highly sensitive spectroscopic technique for trace gas detection. However, the performance of the state-of-the-art laser spectroscopic sensors is still insufficient for some high-precision applications. Here, we demonstrate optical phase-modulation amplification by operating a dual-mode optical fiber interferometer at destructive interference for ultrasensitive carbon dioxide detection. With a 50 cm long dual-mode hollow-core fiber, amplification of photothermal phase modulation by a factor of nearly 20 is achieved, which enables carbon dioxide detection down to 1 parts-per-billion with a dynamic range of over 7 orders of magnitude. This technique could be readily used to improve the sensitivity of phase modulation-based sensors with a compact and simple configuration.

Soft Optomechanical Systems for Sensing, Modulation, and Actuation

AbstractSoft optomechanical systems have the ability to reversibly respond to optical and mechanical external stimuli by changing their own properties (e.g., shape, size, viscosity, stiffness, color or transmittance). These systems typically combine the optical properties of plasmonic, dielectric or carbon‐based nanomaterials with the high elasticity and deformability of soft polymers, thus opening the path for the development of new mechanically tunable optical systems, sensors, and actuators for a wide range of applications. This review focuses on the recent progresses in soft optomechanical systems, which are here classified according to their applications and mechanisms of optomechanical response. The first part summarizes the soft optomechanical systems for mechanical sensing and optical modulation based on the variation of their optical response under external mechanical stimuli, thereby inducing mechanochromic or intensity modulation effects. The second part describes the soft optomechanical systems for the development of light induced mechanical actuators based on different actuation mechanisms, such as photothermal effects and phase transitions, among others. The final section provides a critical analysis of the main limitations of current soft optomechanical systems and the progress that is required for future devices.

Broadband all-fiber optical phase modulator based on photo-thermal effect in a gas-filled hollow-core fiber

We report broadband all-fiber optical phase modulation based on the photo-thermal effect in a gas-filled hollow-core fiber. The phase modulation dynamics are studied by multi-physics simulation. A phase modulator is fabricated using a 5.6-cm-long anti-resonant hollow-core fiber with pure acetylene filling. It has a half-wave optical power of 289 mW at 100 kHz and an average insertion loss 0.6 dB over a broad wavelength range from 1450 to 1650 nm. The rise and fall time constants are 3.5 and 3.7 μs, respectively, 2–3 orders of magnitude better than the previously reported microfiber-based photo-thermal phase modulators. The gas-filled hollow-core waveguide configuration is promising for optical phase modulation from ultraviolet to mid-infrared which is challenging to achieve with solid optical fibers.

Study on the applicability of photoswitch molecules to optically-controlled thermal energy in different organic phase change materials

As a photoresponsive molecule, azobenzene molecule can realize optically-controlled phase change through the regulation of molecular structure, and store photothermal solar energy and phase change heat simultaneously, expected to achieve long-term heat storage and optically-controlled heat release of phase change materials (PCMs). In this paper, the photo-triggered controllable phase change behavior of two different grafting groups (AZO-A-14, AZO-O-14) photoswitch molecules mixed with straight-chain alkane, fatty alcohol and fatty acid PCMs at different ratios was investigated. The results show that the photoswitch molecules are more suitable for the phase change temperature control of fatty alcohol or fatty acid PCMs, and this is true for different concentrations. Using a photoswitch with similar polarity to the substrate, the trans-photoswitch that are not fully isomerized as well as cis-photoswitch can be well dispersed in PCMs, thus hindering their nucleation. In addition, the total enthalpies of the two photoswitch molecules are 233.45 J/g and 229.21 J/g, and the enthalpies of the optically-controlled PCMs ranged from 176.15 J/g to 229.06 J/g. For fatty acid, the doped photoswitch molecules can significantly improve the total energy storage density, and considering the energy storage density and temperature difference of the optically-controlled phase change, the combination of alcohol and ether-grafted optically-controlled PCMs is the best choice. This study provides ideas for the improvement, development and application of optically-controlled PCMs in the future.

High thermal storage ability and photothermal conversion capacity phase change capsule with graphene oxide covalently grafted silica shell

Preparation of phase change materials with energy collection, conversion and storage functions is considered to be an important way to solve the energy shortage problem. Hence, a novel phase change capsule (EP@MGO) with photothermal conversion function was innovatively designed. In the process of preparing EP@MGO, the modified graphene oxide (MGO) layer was covalently anchored on the surface of the phase change capsule encapsulated by silica shell (EP) through Si-O-Si bonds, in which MGO was obtained by modifying GO nanosheets with isocyanate propyl triethoxysilane. The as-prepared EP@MGO microcapsule presents favorable latent heat storage capacity, with enthalpy of 139.8 J/g and high encapsulation efficiency of 83.6%. Besides, the thermal stability, leakage-proof property, durability, and thermal reliability of EP@MGO were enhanced significantly due to the physical protection effect provided by the SiO2-MGO double-layer shell. Moreover, the covalently MGO-grafted silica shell endows EP@MGO with high thermal conductivity (1.603 W/m·K), which improves its thermal management efficiency. More importantly, EP@MGO exhibits the potential ability to effectively utilize ultraviolet and visible light. In detail, the absorbance of EP@MGO increased by ∼192% in the ultraviolet and visible light region (200–800 nm), and the photothermal conversion efficiency under near infrared (NIR) region as high as 64.4%, which has negligible change (64.2%) even after 50 times heating-cooling cycle. Therefore, the phase change capsule EP@MGO provides a new idea for realizing efficient utilization of solar energy, and exhibits the application potential in biomedical treatment, smart textiles, and solar thermal collector.

Correlation between amplitude and phase photothermal signals based on Kramers–Kronig relations: Application to the investigation of interfacial thermal resistance in multilayers

A general feature of frequency-domain photothermal (PT) experiments is that the signal phase follows the derivative of the log –log-amplitude. This is the consequence of the Kramers–Kronig (K–K) relations between real and imaginary parts of the thermal response of the system, represented by its thermal impedance. Simple expressions allow determining the phase from the amplitude, both theoretically and experimentally. They stem from the local Hilbert transform in differential form, instead of the traditional integral form which requires broadband information. These expressions are applied to the thermal impedance of a layered system. The measurements were performed in an earlier publication by photothermal radiometry (PTR) method to determine the interfacial thermal resistance between a 50 nm Ti layer and a steel or Si substrate. In this case, high frequency measurements are the most relevant, but they are also most prone to artifacts and background noise. It is concluded that the amplitude and phase results of Ti/steel samples are correctly linked to one another, but that the phase of Ti/Si samples violates the K–K relations at high frequency, probably due to a different signal generation mechanism than the PT one. The fact that PT phenomena are consistent with the K–K relations opens the possibility to check the self-consistency of the results obtained by PTR or by other related PT methods. It also reveals that the PT phase carries the same information as the signal amplitude, less a scaling factor that incorporates the thermal effusivity of a layer in the system.

Influences on Quantitative Nitriding Layer Thickness Measurements using Model-Based Photothermal Radiometry

Abstract In nitriding furnaces, the nitriding result is currently only controlled indirectly via the nitriding potential based on gas sensors. Detrimental properties such as soft spots, insufficient compound layer thickness or strongly porous zones, which might result from reduced surface reactivity, are thus only detected post-process. Therefore, in-process measurements of the layer formation promise a real benefit for energy efficiency and process quality enhancement. Photothermal radiometry is a promising contactless method for layer inspection that so far showed qualitative correlations of the photothermal phase signal with material parameters and layer thicknesses. In this article, thickness and thermal conductivity of the compound layer are quantitatively determined by using a physical signal model for a least-squares approximation of in-process measured photothermal phase signals. In addition, the influence of roughness and surface curvature is investigated, with the model-based photothermal layer thickness measurement showing robustness to different surface conditions and allowing quantification of the layer thickness with uncertainties &lt; 1 μm even during in-process measurement inside an industrial nitriding furnace.

Frequency-Division-Multiplexed Multicomponent Gas Sensing with Photothermal Spectroscopy and a Single NIR/MIR Fiber-Optic Gas Cell.

We report a multicomponent gas sensor based on hollow-core fiber (HCF) photothermal spectroscopy with frequency-division multiplexing (FDM). A single antiresonant HCF (AR-HCF) is used as the gas cell, which supports broadband transmission from near-infrared (NIR) to mid-infrared (MIR), covering the absorption lines of water vapor (H2O) at 1.39 μm, carbon dioxide (CO2) at 2.00 μm, and carbon monoxide (CO) at 4.60 μm. The NIR and MIR pump lasers at the above wavelengths are coupled into the AR-HCF from the opposite ends and modulated at 7.5, 8.0, and 8.5 kHz, respectively, to produce photothermal phase modulations at different frequencies. A common probe Fabry-Perot interferometer at 1.55 μm is adopted to detect the phase modulations, which are demodulated simultaneously using three lock-in amplifiers at the respective second harmonic frequencies. With a 13-cm-long AR-HCF, simultaneous detections of H2O, CO2, and CO are demonstrated with the limits of detection (LODs) of 2.7 ppm, 25 ppb, and 9 ppb for 1 s lock-in time constant, respectively. The LODs go down to 222, 1.5, and 0.6 ppb, respectively, for 1000 s averaging time. The photothermal signals of CO and CO2, which are humidity-level dependent, are well calibrated by use of the measured H2O signal. The multicomponent gas sensor is compact in configuration and shows good stability with signal fluctuation less than 1.7% over 2 h.