Temperature-sensitive Materials Research Articles

Thermal energy storage composites with preformed expanded graphite matrix and paraffin wax for long-term cycling stability and tailored thermal properties

Harvesting solar energy, preventing hot spots in electronics, transport of temperature-sensitive materials, and capture and repurposing of thermal energy require a latent heat thermal energy storage (TES) system to store/discharge heat repeatedly. For the practical application of phase change material (PCM) composites within TES systems, reliable thermal performance throughout its operational lifetime is essential. Nevertheless, the reliability of thermal conductivity in multi-phase composites over relevant numbers (>103) of melt/freeze cycles has barely been studied, particularly for composites containing fillers for thermal conductivity enhancement. Here, we introduce a preform-type expanded graphite (EG)/paraffin wax composite possessing highly robust heat transfer and storage properties even after 10,000 melt/freeze cycles. To achieve such excellent reliability, comparative studies on the combined influence of fabrication process, particle size, EG vol%, binder amount, and compaction on both magnitude and robustness of thermal conductivity were undertaken. Our parametric study has yielded a trade-off between thermal conductivity and latent heat. Based on our modeling, 20 vol% EG approaches the case where all EG particles are well-connected thermally while 10 vol% EG is close to loosely connected fillers in the matrix. Thermal conductivity of our paraffin composites containing 20 vol% EG (25.1 W·m−1·K−1) is highest among other EG/paraffin composites without aligned EG in the literature. After 10,000 thermal cycling, negligible conductivity fading was observed for the 10 vol% EG composite, while reduction in latent heat remained within 10% for all 10, 14, 17 and 20 vol% EG samples. We anticipate this work provides insight on suitable recipe for desirable magnitude and robustness of thermal conductivity of EG/paraffin composites.

Double-sided photonic crystal fiber (PCF) temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR)

A double-sided photonic crystal fiber (PCF) temperature and refractive index (RI) sensor based on surface plasmon resonance (SPR) is reported to simultaneously measure temperature and RI. An arc groove covered with gold is filled with chloroform for temperature detection. The D-shaped plane coated with silver is in direct contact with the analyte to provide the RI. Two independent channels distinguish temperature and RI changes, thus completely solving the cross-sensitivity problem. The sensing characteristics of the plane coating, arc coating, and inner ring coating are discussed. The influence of gold film closure on the optimum RI measurement range was identified, and the best sensing structure of chloroform as a temperature-sensitive material is obtained. The sensing characteristics of different types of metal films are investigated. It is concluded that the band separation may be achieved by plating gold film and silver film in the arc groove and D-plane, respectively. The influence of the central angle of the arc groove on the sensor characteristics was investigated. High-order resonance may be avoided at a 180° center angle. The influence of the thickness of the metal film on the sensitivity of the sensor is studied numerically, and the optimal coating thickness is 50 nm. This work simplifies the selection of the RI range of sensing materials and provides a new approach to solve the high-order resonance and band interference in SPR multi-parameter sensors.

Evaluation of the High- and Low-Temperature Performance of Asphalt Mortar Based on the DMA Method

Asphalt mortar is a typical temperature-sensitive material that plays a crucial role in the performance of asphalt mixture. This study evaluates the high- and low-temperature performance of asphalt mortar based on the dynamic mechanical analysis (DMA) method. Temperature-sweep tests of asphalt mortars were conducted using the DMA method under fixed strain level, frequency, and heating rate conditions. The dynamic mechanical response curves, characteristic temperature, and other indices were obtained and used to investigate the high- and low-temperature performance of asphalt mortar. The results showed that the phase transition temperatures T1, T0, and Tg can be used to evaluate the low-temperature performance of asphalt mortar. Additionally, they had a good linear relationship, and the evaluation results were consistent. Meanwhile, T2, E60, and tan(δ)max indicators can effectively evaluate the high-temperature performance of asphalt mortar. Asphalt plays a key role in the performance of asphalt mortar. Mortars with neat asphalt A70 and modified asphalt AR had the worst and best high- and low-temperature performances, respectively. Furthermore, the finer gradation improved the low-temperature performance of asphalt mortar, while the coarser gradation improved the high-temperature properties of modified asphalt mortars but had the opposite effect on neat asphalt A70.

Synthesis of polymeric nitrogen with non-thermal radio frequency plasma

Polymeric nitrogen (PN) is potentially a green catalytic material due to its Lewis base property, and a high-energy density material (HEDM) due to its considerable energy storage and the environment-friendly decomposition product, nitrogen gas. Most research has focused on theoretical studies and various structures were proposed, while a few successful experiments were carried out. Plasma technology, as a viable synthesis technique for materials, may provide new possibilities for polymeric nitrogen. In this review, the polymeric nitrogen study, the plasma technology, and its potential catalytic applications for polymeric nitrogen synthesis are reviewed and summarized. Polymeric nitrogen synthesis requires extremely high temperature and high pressure with traditional thermal method and is thermodynamically unstable, while some PNs exhibit excellent catalytic activity. High pressure, cations and substrates are important for polymeric nitrogen synthesis and stabilization. Plasma processes, full of energetically active particles, can operate under mild conditions and is very good for temperature-sensitive materials. Thus, plasma has a promising potential application for polymeric nitrogen synthesis. Proper precursors and substrates are important in order to increase products, which are necessary for further exploitation of polymeric nitrogen. With better understanding of the mechanism of plasma treatment, it will have wider applications.

Mild Sol–Gel Conditions and High Dielectric Contrast: A Facile Processing toward Large-Scale Hybrid Photonic Crystals for Sensing and Photocatalysis

Solution processing of highly performing photonic crystals has been a towering ambition for making them technologically relevant in applications requiring mass and large-area production. It would indeed represent a paradigm changer for the fabrication of sensors and for light management nanostructures meant for photonics and advanced photocatalytic systems. On the other hand, solution-processed structures often suffer from low dielectric contrast and poor optical quality or require complex deposition procedures due to the intrinsic properties of components treatable from solution. This work reports on a low-temperature sol–gel route between the alkoxides of Si and Ti and poly(acrylic acid), leading to stable polymer–inorganic hybrid materials with tunable refractive index and, in the case of titania hybrid, photoactive properties. Alternating thin films of the two hybrids allows planar photonic crystals with high optical quality and dielectric contrast as large as 0.64. Moreover, low-temperature treatments also allow coupling the titania hybrids with several temperature-sensitive materials including dielectric and semiconducting polymers to fabricate photonic structures. These findings open new perspectives in several fields; preliminary results demonstrate that the hybrid structures are suitable for sensing and the enhancement of the catalytic activity of photoactive media and light emission control.

Simultaneous measurement of magnetic field and temperature based on photonic crystal fiber plasmonic sensor with dual-polarized modes

A photonic crystal fiber (PCF) based on surface plasmon resonance (SPR) sensor with two orthogonally polarized core modes is designed to achieve simultaneous measurement of magnetic field and temperature. According to the sensing principle, four large ring microfluidic detection channels coated with silver-tantalum pentoxide (Ag-Ta2O5) composite films are symmetrically distributed in the PCF cladding, where the upper and lower channels are filled with magnetic fluids (MFs), and the temperature-sensitive material is infiltrated into the left and right channels. The refractive index (RI) of the MFs has strong dependence on the magnetic field and temperature, while the RI of the temperature-sensitive material is merely affected by the temperature. Therefore, the information on the magnetic field and temperature carried by two orthogonally polarized core modes can be separated. The effect of the structure parameters of the proposed sensor on the sensing performance are evaluated through the optical loss spectrum based on finite element method (FEM). The numerical results show that a dual-parameter sensing matrix on simultaneous measurement of the magnetic field and temperature is established, revealing a magnetic field sensitivity of 265 pm/Oe in the range of 20–300 Oe and a temperature sensitivity of − 1410.7 pm/°C in the range 20–80 °C. The designed sensor overcomes the cross-sensitivity problem when the magnetic field and temperature are measured at the same time, which has a potential application in the fields of dual-parameter sensing.

Switched electrochemical sensor for hydroquinone based on rGO@Au, monoclinic BiVO4 and temperature-sensitive polymer composite material

In this paper, a temperature-controlled “On-Off” electrochemical sensor for the detection of hydroquinone (HQ) is constructed by using a composite film of temperature-sensitive polymer poly (N-vinylcaprolactam) (PNVCL), the nanomaterial rGO@Au and the monoclinic bismuth metavanadate (m-BiVO4). The sensor exhibits good temperature sensitivity and reversibility. When the temperature drops below the Lowest Critical Solution Temperature (LCST) of the PNVCL, the PNVCL will be in a “stretched” state, which hinders the electron exchange between hydroquinone and the surface of the electrode, presenting an “Off” state for the sensor. On the contrary, when the temperature exceeds the LCST, the PNVCL will be in a “contracted” state, which hydroquinone can perform an effective redox process and generate a response current, showing an “On” status. Due to the good electroconductivity and electrocatalytic ability of rGO@Au and m-BiVO4, the proposed sensor showed excellent detection performances. Hence, the sensor shows wide linear ranges (2.0 to 30.0 μM and 30.0 to 152.0 μM) and low limit of detection (0.6 μM). In addition, the “On-Off” electrochemical sensor may provide new ideas for the application of intelligent polymers.

Fiber optic high temperature sensor based on ZnO composite graphene temperature sensitive material

The working temperature of the cable is particularly important for the safe operation of the power system, which requires high temperature detection for its working environment, but the sensitivity of the ordinary optical fiber temperature sensor in the high temperature state cannot meet this demand. For this purpose, an optical fiber high temperature sensor based on ZnO composite graphene temperature sensitive material is developed in this paper. MMF-TSCF-MMF temperature sensing unit is composed of two sections of multimode fiber (MMF) and a tapered seven core fiber (TSCF). Three different shapes of ZnO@Gr (ZnO composite graphene) temperature-sensitive materials were prepared by hydrothermal method. The experimental results show that the sensor has high stability and good interference effect. Meanwhile, the wavelength sensitivity reached 0.33268 nm/°C in a temperature measurement range of 89–98 °C. The fiber sensor is used for precision temperature measurement of cable temperature in fields such as electrical engineering due to its high temperature sensitivity, small size and low cost.

CFD analysis of environmental impacts on a thermochromic smart window

Thermochromic (TC) glazing is an advanced smart window technology that can help to achieve nearly zero-energy buildings. The glazing temperature that affects TC thermo-optical properties directly impacts its energy-saving performance. However, the impacts of solar radiation and natural convection occurring on this temperature-sensitive material are not yet fully understood. Compared to previous focuses on material properties and energy evaluation, this study aimed to provide a different view from thermo-fluid dynamics on the heat transfer characteristics of a TC window, with impacts of environmental factors addressed. A validated Computational Fluid Dynamics (CFD) model identifies the environmental impacts on the TC glazing temperatures under the coupled radiative and convective heat transfer. Furthermore, a theoretical model was developed with an empirical factor obtained from CFD results. It enables a simple calculation to obtain the TC glazing’s temperature by using solar factors, outdoor temperatures and optical properties. The model suggests that the temperature difference between the TC glazing and the ambient is a function of absorbed solar irradiation (∝q̇total0.75). The predictive model is then tested using typical climate conditions in three cities in China with different solar angles, which demonstrates good agreement with an average absolute error of 5% compared to simulated glazing temperature. This estimation method can further assist in material design, product selection and Building Energy Simulations to achieve a TC window design that is ‘smart’ on seasonal change requirements for different regions.

Microstructure and Thermal Deformation Behavior of Hot-Pressing Sintered Zr-6Al-0.1B Alloy.

Zr-6Al-0.1B alloy rich in Zr3Al phase is prepared by hot-pressing sintering. The thermal deformation behavior of sintered Zr-6Al-0.1B is analyzed by isothermal compression tests at deformation temperatures of 950, 1050, and 1150 °C with strain rates of 0.01, 0.1, and 1 s−1. The results indicate that at the early stage of thermal deformation, the stress increases rapidly with the increase of strain and then reaches the peak value. Subsequently, the stress decreases with the increase of strain under the softening effect. On the whole, the true stress-strain curve shifts to the high stress area with the increase of strain rate or the decrease of deformation temperature, so the sintered Zr-6Al-0.1B alloy belongs to the temperature and strain rate sensitive material. For the microstructure evolution of sintered Zr-6Al-0.1B during the isothermal compression, the high strain rate can improve the grain refinement. However, because sintered Zr-6Al-0.1B is a low plastic material, too high strain rate will exceed the deformation capacity of the material, resulting in an increase in defects. The increase of deformation temperature also contributes to grain refinement, but when the temperature is too high, due to the decomposition of Zr3Al phase, the deformation coordination of the material decreases, leading to the increase of the probability of the occurrence of defects. This study verified the feasibility of hot-pressing sintering to prepare Zr-6Al-0.1B alloy rich in Zr3Al phase and laid the foundation of “hot-pressing sintering + canning hot-extrusion” process of Zr-6Al-0.1B alloy components.

Experiment and Analysis of Temperature Sensing of Microstructured Fiber with Silver and PDMS Films.

In this study, the silver mirror reaction was used to coat the silver film on the surface of self-made microstructured fiber (MSF) to stimulate the surface plasmon resonance effect, and Polydimethylsiloxane (PDMS) with a high thermal-optical coefficient was coated on the silver film as temperature-sensitive material. The MSF with silver and PDMS films was coupled with multi-mode fiber on both sides to form the temperature sensor. In this sensor system, the energy is coupled into the cladding of the microstructure fiber by multi-mode fiber, and the surface plasmon resonance can be further excitated in the MSF. When the temperature of the external environment changes, the refractive index of PDMS will also change. At this time, combined with the surface plasmon resonance effect, a resonant absorption peak corresponding to the temperature appears in the transmission spectrum so that the temperature can be measured quickly and accurately. We found that, in the temperature range of 35 °C to 95 °C, the average temperature sensitivity of the sensor during heating and cooling was −0.83 nm/°C and −0.84 nm/°C, respectively. The advantages of this sensor are the simple structure, convenient operation and good reversibility. The relative sensitivity deviation value (RSD = 0.0059) showed that the sensor has high stability. The temperature sensor based on MSF has favorable prospects for use in fields such as medical treatment, biochemical detection and intelligent monitoring.

The effects of interfacial dipole caused by annealing-free Al-doped NiOx in efficient perovskite solar cells

Recent researches show that nickel oxide (NiOx) thin films can be utilized as an efficient and stable hole transport layer (HTL) in inverted planar perovskite solar cells (PSCs) replacing costly and chemically unstable organic materials. Nevertheless, thermal annealing process is necessary for NiOx made by conventional methods with metallic dopants, which is not applicable to flexible substrates with low melting points or temperature-sensitive materials. In this work, annealing-free Al-doped NiOx nano-particles (NPs) were synthesized and employed as a HTL in PSCs. Without using any Dimethyl sulfoxide (DMSO) additive in devices, the electrical conductivity, morphology, external quantum efficiency, and power conversion efficiency were all significantly enhanced after 2% Al doping in NiOx. The Ultraviolet Photoemission Spectroscopy (UPS) was conducted to explore the mechanisms behind the device improvements. An interfacial dipole of 0.3 eV was found between the ITO electrode and the NiOx layer directing away from the active layer, boosting the hole extraction efficiency at ITO/MAPbI3 (MA = methylamine) interface. This work not only provides a deep insight of the ITO/NiOx NPs/perovskite interface but also proposes a new strategy for further development of highly efficient and reliable PSCs.

A real-time temperature responsive material based on partial inverse opal photonic crystals and cholesteric liquid crystals

In this paper, we fabricated a temperature-sensitive material with a partial inverse opal structure, which can reversibly and quickly identify small temperature changes at room temperature and show significant color differences. First, we synthesized silica microsphere and prepared silica photonic crystals (PCs), then we composited PCs with polymer. After covering the mask, we prepared partial inverse opal silica PCs template by using selective etching. The temperature-sensitive liquid crystals (LCs) composed of cholesterol oleyl carbonate (COC), cholesterol nonanoate (CPE) and cholesterol benzoate (CBZ) were filled in partial inverse opal silica PCs template. In the end, we sealed the film by methyl methacrylate (MMA) and polyethylene glycol diacrylate (PEGDA). In this way, we prepared the fast temperature-sensitive dual-opal PCs/LCs composite film, and studied the mechanism of temperature regulation on material display mode. As the temperature gone from 26 °C to 30 °C, the material changed colors rapidly from red to blue. The result showed that this PCs/LCs composite film had well temperature response performance, which can monitor slight environmental temperature change. By selective etching the material, we designed PCs film patterns. The different patterning states displayed and changed fast at different temperatures, showing that the material had a good application prospect in the fields of temperature sensor, anti-counterfeiting, and display device.

Highly Sensitive Flexible Temperature Sensor Made Using PEDOT:PSS/PANI

This work proposes a design, fabrication, and characterization of flexible temperature sensors using temperature-sensitive materials, which are applied using a drop coating method. Temperature-sensitive materials were fabricated by mixing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) with polyaniline (PEDOT:PSS/PANI). The temperature coefficient of resistance reached −0.803%/°C. Moreover, the detection resolution reached 0.1 °C and had a fast response time of 200 ms. In addition, the sensor can sense spatial temperatures. The sensor has the advantages of low cost, a simple preparation process, and the potential to be used in medical rehabilitation and early disease prevention.

Dual-beam laser-based processing of tribological polymer coatings

Polyether ether ketone (PEEK) is a potential candidate to substitute state-of-the-art friction-reducing coatings due to its excellent properties in terms of temperature resistance and friction reduction. Conventionally, microparticulate PEEK is applied to a component and melted in an oven-based process where the entire component is heated above the melting temperature of PEEK (Tmelt = 340°C) for minutes to hours. Due to the high thermal load on the component, temperature-sensitive materials cannot be processed without a significant reduction in the hardness of the component. One approach to overcome this drawback is to melt the microparticulate PEEK layer with laser radiation. Due to the achievable high heating and cooling rates, laser treatment offers the possibility to obtain the necessary melting temperature within the coating while reducing the thermal load on the substrate material. Still, a pre-heating of the substrate surface is necessary to achieve a high PEEK layer adhesion to the substrate surface. In this study, a laser-based dual-beam approach is presented in which both the preheating of the substrate and the melting of the PEEK layer are implemented with laser radiation.

Luminescent composites by in-suit encapsulating dye in IRMOF-3 for ratiometric temperature sensing and tunable white light emission

Metal-organic frameworks (MOFs) as a promising scaffold for functional guests, are known for the adjustable structures and various porosity, which can improve the luminescence performance by encapsulating fluorophores. Herein, the organic fluorescent dyes of rhodamine B (RhB) and fluorescein (FL) are immobilized in luminescent IRMOF-3, named as Dye@IRMOF-3, by a simple in-suit encapsulation reaction. Dye@IRMOF-3 are characterized by X-ray diffraction (XRD), gas adsorption analysis, thermogravimetric (TG), Fourier transform infrared (FTIR) and luminescent experiments. Dye@IRMOF-3 composites overcome the intrinsic problem of dye quenching caused by aggregation in solids, and show the fluorescence of both IRMOF-3 and dye molecules. In luminescence temperature sensing experiments, the relative sensitivity range of RhB@IRMOF-3 and FL@IRMOF-3 are from 0.60 to 0.87%°C−1 (temperature range of 20–70 °C) and 0.47–0.66%°C−1 (temperature range of 20–80 °C), respectively, making them promising colorimetric thermometer for field temperature measurements. Meantime, the emission spectrum of RhB/FL@IRMOF-3 can cover the whole visible light, whose CIE coordinates (0.330,0.342) are quite close to those of the pure white light (0.333,0.333), showing potential applications in the field of white light emission. This work provides a promising method for the synthesis of Dye@MOF luminescent materials and provides a new way to develop temperature-sensitive and white-emitting MOF materials by encapsulating different dye molecules.

A safer organic cathode material with overheating self-protection function for lithium batteries

Rechargeable lithium batteries (LBs) have been widely applied in portable devices, electric vehicles (EVs) and grid energy storage systems due to their higher energy density, long cycle life and lack of memory effect. However, if operated improperly such as thermal impact, mechanical damage or short-circuiting, it will cause the vast heat accumulation of LBs, finally fires or explosions. Here, we report a novel concept that the temperature-sensitive conductive polymer-based materials (P3OT@CNT and P3BT@CNT nanocomposites) as cathode materials with intrinsic overheating self-protection function enabled by removing active anions can mitigate the safety concern of LBs. In normal operation conditions, both P3OT@CNT and P3BT@CNT display a better electrochemical performance compared with the reported anion-active cathode materials. More importantly, the thermal dedoping of electroactive PF6- from P3OT or P3BT matrix when the battery temperature reaches to a given high temperature can provide overheating self-protection for LBs, avoiding the occurrence of thermal runaway. During the charging process, the thermal dedoping of PF6- causes the battery voltage to not rise, namely the loss of charging function. This abnormal voltage signal can offer an early warning of battery overheating, allowing timely handling and preventing the occur of thermal runaway of battery. When discharged, the battery can be rapidly switched off with delivering little capacity, avoiding the continuous heat accumulation and preventing battery from thermal runaway. This work provides a new thermal protection strategy for safer LBs, utilizing the intrinsic overheating protection function of cathode materials without introducing extra thermal protection elements to battery.

Improving LCC Series-Based Wireless Power Transfer System Output Power at High Temperature

Adding a core to a coupling coil can improve transmission efficiency. However, the added core causes the self-inductance of the coupling coil to increase at a high temperature due to the temperature-sensitive property of the core material’s permeability. The self-inductance increases, causing the resonance frequency to shift down, thereby decreasing the output power. The 3 dB bandwidth of the system can learn of the correspondence between the output power and the resonance frequency. In order to make sure that the output power does not excessively decrease at a high temperature, this study employs a simulation for the LCC-S-based wireless power transfer system. Adding a minor resistance to shift down the lower cutoff frequency ensures that the resonance frequency yielded by the temperature rise can be higher than the lower cutoff frequency, making the output power higher than half of the maximum. Then, an adjustment on the compensation capacitances on the resonant circuit elevates the output power more. The outcomes are consistent with the prediction. Adding the core to the coupling coil improves transmission efficiency; increasing the bandwidth of the system excessively decreases the output power decline at a high temperature for the temperature-sensitive core material permeability.

PCF based surface plasmon resonance temperature sensor with ultrahigh sensitivity

A simple photonic crystal fiber (PCF) temperature sensor with high sensitivity based on the principle of surface plasmon resonance (SPR) is proposed. The cladding of the sensor is mainly composed of two layers of square arranged holes. The inner wall of the outer air holes is selectively plated with gold film, and the outer holes are filled with the temperature sensitive material chloroform to promote the coupling of the surface plasmon mode and the fundamental mode, thereby improving the sensitivity. The finite element method is used to analyze the effects of the temperature on the performance of the sensor. Through tailoring the structural parameters, it is shown that the maximum sensitivity of the sensor can reach up to − 10.4 nm/℃ in the range of 0–60 ℃ with high resolution and good linearity. Such appealing characteristics make the sensor be one of the important potential candidates in the field of temperature sensing.

Surface plasmon resonance (SPR) based temperature and magnetic field sensor in a dual-core D-shaped photonic crystal fiber (PCF)

A high sensitivity surface plasmon resonance (SPR) based temperature and magnetic field sensor in a dual-core D-shaped photonic crystal fiber (PCF) with two types of holes is reported. The flat surface of the dual-core D-shaped PCF is coated with ethanol as the temperature-sensitive material. A large diameter hole coated with a gold ring is filled with a magnetic fluid as a magnetic field-sensitive material. Using the finite element method (FEM), the electric field distribution mode is simulated, and the loss spectra of the temperature sensing channel (channel I) and magnetic field sensing channel (channel II) are calculated. The influence of the types of metal films and rings, large hole diameter, small hole diameter, and gold film and gold ring thicknesses on the sensor performance are discussed. The results showed that the reported sensor is able to measure temperature and magnetic field independently and simultaneously due to its dual channels. The influence of temperature on magnetic field measurements is reduced by reducing the hole diameter. The results show that the temperature sensitivity is 1.151 nm/°C and the correlation coefficient is 0.9954 from 20 to 70 °C. The magnetic field intensity sensitivity is 0.0779 nm/Oe from 25 to 200 Oe and 0.0212 nm/Oe from 200 to 275 Oe with correlation coefficients of 0.9937 and 0.9989 across these ranges. This high sensitivity D-shaped PCF sensor will promote the development of high-performance dual-parameter devices.