Temperature-sensitive Materials Research Articles

Temperature depended resistive property of fermented soybeans (Japanese natto) as a temperature sensor material

Carbon-based temperature-sensitive materials have become recent topics of interest due to high demands of human sensing. To enable the practical use of these temperature sensing devices, high sensitivity, easy fabrication and disposal, and low cost are essential characteristics that should be considered. However, all these characteristics do not appear simultaneously in existing sensors. In this study, we propose and fabricate a sensitive temperature sensor using fermented soybeans (Japanese natto) as the sensing element. Natto is a naturally derived material with temperature-dependent resistance and low environmental load. Moreover, its fabrication and disposal costs are low. The changes in the resistance of the natto sheet are shown to be dependent on its water content, and a temperature coefficient of resistance of 1.15% °C−1 is achieved. The fabricated sensor shows an experimental temperature sensitivity of at least 0.1 °C. These results indicate the promising potential of using the natto sheet as a temperature sensing element.

Promotion of wound healing by a thermosensitive and sprayable hydrogel with nanozyme activity and anti-inflammatory properties

The rapid healing of wounds requires strategies that relieve oxidative stress resulting from overloaded free radicals and which promote angiogenesis, collagen deposition, and re-epithelialization of the wound. Nickel ions have been reported to be correlated with angiogenesis. However, several applications of metal salts or oxides to wounds lead to increased toxicity. The nickel metal-organic framework (Ni MOF) nanorods described herein can slowly release nickel ions, resulting in reduced toxicity and improved wound healing rates. More importantly, the Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) nanorods with well-defined structures, superior conductivity and many catalytic sites showed superoxide dismutase (SOD)-like enzyme activity and scavenged various free radicals. In addition, the Ni3(HITP)2 nanomaterials contributed to promotion of the migration of fibroblasts, angiogenesis and macrophage polarization from M1 to M2. The aqueous solution of Pluronic F127, a temperature-sensitive, nontoxic and phase-changing hydrogel material, was shown to be an effective choice for injectable and sprayable medical dressings. The Ni3(HITP)2 MOF nanomaterials can be effectively encapsulated with the F127 hydrogel to achieve continuous long-term therapeutic effects. The toxicity test results suggested that the Ni3(HITP)2 MOF nanomaterials exhibited excellent biosafety and no observable toxicity or side effects in mice. Therefore, the Ni3(HITP)2 MOF nanorods hold promising potential in the biomedical field, and this work provides an effective solution to wound therapy.

Low-Temperature Route to Direct Amorphous to Rutile Crystallization of TiO2 Thin Films Grown by Atomic Layer Deposition

The physicochemical properties of titanium dioxide (TiO2) depend strongly on the crystal structure. Compared to anatase, rutile TiO2 has a smaller bandgap, a higher dielectric constant, and a higher refractive index, which are desired properties for TiO2 thin films in many photonic applications. Unfortunately, the fabrication of rutile thin films usually requires temperatures that are too high (>400 °C, often even 600–800 °C) for applications involving, e.g., temperature-sensitive substrate materials. Here, we demonstrate atomic layer deposition (ALD)-based fabrication of anatase and rutile TiO2 thin films mediated by precursor traces and oxide defects, which are controlled by the ALD growth temperature when using tetrakis(dimethylamido)titanium(IV) (TDMAT) and water as precursors. Nitrogen traces within amorphous titania grown at 100 °C inhibit the crystal nucleation until 375 °C and stabilize the anatase phase. In contrast, a higher growth temperature (200 °C) leads to a low nitrogen concentration, a high degree of oxide defects, and high mass density facilitating direct amorphous to rutile crystal nucleation at an exceptionally low post deposition annealing (PDA) temperature of 250 °C. The mixed-phase (rutile–brookite) TiO2 thin film with rutile as the primary phase forms upon the PDA at 250–500 °C that allows utilization in broad range of TiO2 thin film applications.

Aging processes in the nanostructured temperature-sensitive ceramic materials

Aging processes in the two types of temperature-sensitive Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics (two-phase and with different amount of NiO phase) as well as thick films base on Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics were investigated. It is shown for Cu0.1Ni0.8Co0.2Mn1.9O4 ceramics prepared at 1170 °C with addition treatment at 850 °C that the post-separation process of the second phase continue under heat at temperatures of 125 and 170 °C. It has been found that higher thermal aging leads to more pronounced changes in electrical resistance. Addition temperature influences contribute to the stabilization of ceramic parameters. The aging test at 170 °C results in a 7.5% reduction in electrical resistance, while at 125 °C this value is only 6%. It is shown that NiO phase additives formed during sintering of Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics and located near the grain boundaries of ceramics inhibit the aging process in these materials. This effect is characteristic of fine-grained ceramics obtained by thermal energy converted during sintering. It is established that the kinetics of aging in Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics is described by the relaxation function of DeBast-Gillard or Williams-Watts, regardless of the composition of the ceramics. The aging kinetics in thick films based on Cu0.1Ni0.1Co1.6Mn1.2O4 ceramics at 170 °C is also adequately described by the compression-exponential relaxation function.

Highly sensitive temperature sensor based on a liquid crystal selectively infiltrated two-core photonic crystal fiber

This article proposes a temperature sensor based on liquid crystal selectively filled two-core photonic crystal fiber featuring high sensitivity and compact structure. In order to achieve the purpose of compact structure and temperature sensing, we consider to combine the temperature-sensitive material liquid crystal (LC) E7 and photonic crystal fiber to study the performance of temperature sensing. Since the applied electric field and temperature have great influence on the arrangement of liquid crystal molecules, LC as a temperature sensitive material can improve the sensing performance. An air hole filled with LC isolates the two horizontal cores, where the two horizontal cores act as two separate waveguides and the LC core is used to regulate the mode coupling of the two horizontal cores. In the process of transferring light energy from one core to another, the position of the transmission spectrum of the sensor is changed by optimizing the diameter of LC core and horizontal two-core, and then a sensor with high sensitivity and stable performance is designed. The coupling length and transmission spectrum of the sensor are analyzed by using full vector finite element method. By analyzing the wavelength dips of the transmission spectrum, the maximum sensitivity of the proposed temperature sensor can be reached −6.69 nm/℃ at 30 ℃ for Y-polarized (Y-Pol) direction. The main advantages of the sensor proposed in this paper are simple structure and easy to manufacture, high sensitivity and high fitting coefficient.

Influence of Al2O3 content on microstructure, electrical conductivity and adhesion strength of cold sprayed Al-Al2O3 coatings on PEEK substrate

Due to its low process temperature, cold spray (CS) is considered an excellent metallization method to deposit thick coatings on temperature-sensitive polymeric materials. However, in previous studies, the properties (such as electrical conductivity and adhesion strength) of the cold sprayed metallic coating on the polymeric substrate are relatively low. To address this issue, large-sized spherical Al2O3 particles were added into Al powder in different proportions (i.e. 0, 10, 20, 30, 40 wt%) to prepare dense Al-Al2O3 coatings on PEEK by CS. The effect of Al2O3 content on microstructure, deposition efficiency (DE), microhardness, electrical conductivity, and adhesion strength of Al-Al2O3 coatings was systematically studied. Results show that adding an appropriate amount of Al2O3 to the feedstock can effectively improve the Al-Al splat bonding, electrical conductivity, and adhesion strength of the prepared coating on PEEK substrate, which is attributed to the ‘in-situ tamping effect’ of spherical Al2O3 particles. Moreover, the molecular structure of the substrate was not damaged or affected after the impact of Al and Al2O3 particles during the CS process. The prepared Al-Al2O3 coating exhibits better performance and provides a novel approach for polymer metallization.

Synthesis, and characterization of metallic glassy Cu–Zr–Ni powders decorated with big cube Zr2Ni nanoparticles for potential antibiofilm coating applications

Biofilms, are significant component that contributes to the development of chronic infections, especially when medical devices are involved. This issue offers a huge challenge for the medical community since standard antibiotics are only capable of eradicating biofilms to a very limited degree. The prevention of biofilm formation have led to the development of a variety of coating methods and new materials. These methods are intended to coat surfaces in such a way as to inhibit the formation of biofilm. Metallic glassy alloys, in particular, alloys that include copper and titanium metals have gained popularity as desirable antibacterial coating. Meanwhile, there has been a rise in the use of the cold spray coating technique due to the fact that it is a proper approach for processing temperature-sensitive materials. The present study was carried out in part with the intention of developing a new antibiofilm metallic glassy consisting of ternary Cu–Zr–Ni using mechanical alloying technique. The spherical powders that comprised the end-product were utilized as feedstock materials for cold spray coatings to stainless steel surfaces at low temperature. When compared to stainless steel, substrates coated with metallic glassy were able to significantly reduce the formation of biofilm by at least one log.

Study of Bonding Mechanisms in Cold Spray of Metal-to-Polymer through a Numerical Approach

Cold spray (CS) is a low-temperature process that can be used for the metallization of temperature-sensitive materials, such as polymers or polymer matrix composites, so coupling the lightweight of polymers with the wear resistance, physical properties and hardness of metals. The study of the cold spray of metal particles applied to polymers is still in its early stage and the deposition mechanisms underlying the process are not thoroughly understood yet. Moreover, numerical studies of cold spray of metal-to-polymer are almost completely absent in literature. Therefore, aiming to fulfill this gap of knowledge, the scope of this work is to develop a numerical FE model capable of predicting the impact and the adhesion of a micron size metallic particle onto a polymeric substrate. The results from the model were compared with the experimental outcomes found in literature to establish the effectiveness of the model that was used as a powerful tool to better understand the bonding mechanisms and all the related phenomena ruling the CS process of metal-to-polymer.

Low-Temperature Atomic Layer Deposition of Hafnium Oxide for Gating Applications.

We present a novel low-temperature (30 °C) atomic layer deposition process for hafnium oxide and apply the layers as gate dielectric to fabricate devices out of the thermally sensitive topological insulator HgTe. The key to achieving self-limiting growth at these low temperatures is the incorporation of sufficiently long purge times ( ≥150 s) in the deposition cycles. We investigate the structural and compositional properties of these thin films using X-ray reflectometry and photoelectron spectroscopy, finding a growth rate of 1.6 Å per cycle and an atomic ratio of Hf/O of 1:1.85. In addition, we report on the transport properties of the microstructured devices, which are much enhanced compared to previous device generations. We determine a relative permittivity of ∼15 for our HfO2 layers. Our process considerably reduces the thermal load of the samples during microfabrication and can be adapted to a broad range of materials, enabling the fabrication of high-quality gate insulators on various temperature-sensitive materials.

High conductive rGO sheets fabricated by mild, low-cost and scalable plasma-triggered reduction-exfoliation of 3D aerogel-like graphene oxide

The costs associated with the reduced graphene oxide (rGO) reduction process still limit its large-scale production from starting graphene oxide (GO) precursors. As a solution to these problems, we demonstrate a low-cost, chemical-free, fast (∼1 s), and low-temperature (∼140 °C) fabrication of 3D free-standing pure rGO aerogel structure using an electrical plasma-triggered reduction of a casted GO aerogel without destroying of its original 3D physical form. The reduction-exfoliation realized using a Diffuse Coplanar Surface Dielectric Barrier Discharge (DCSBD) plasma source in atmospheric-pressure N2 results in an approximately 105 fold decrease in the GO aerogel resistivity and more than two orders increase of its specific surface area. The basic properties of the rGO thus produced were examined using XPS and SEM and compared with those obtained using a standard thermal reduction method. We believe that the method presented opens new opportunities for low-cost industrial-scale production of porous 3D and 2D rGO structures including their composites and hybrids with temperature-sensitive materials.

Effects of flow fluctuations and buoyancy on heat transfer from a sphere in non-Newtonian nano fluids: Potential for intensification

This work numerically explores the combined effects of buoyancy-induced flow and pulsating velocity for nanofluids (power-law type fluids) over a sphere to ascertain the potential of this approach for process intensification. The pertinent field equations are solved numerically for a range of dimensionless variables as, Richardson number (0 ≤ Ri ≤ 5), amplitude of fluctuations (0 ≤ A ≤ 0.8), frequency of pulsation (π/4 ≤ ω* ≤ π), Reynolds number (5 ≤ Re ≤ 100), power-law index (0.3 ≤ n ≤ 1.5) and Prandtl number (1 ≤ Pr ≤ 100). The aiding-buoyancy flow suppresses the transient effects of the flow pulsations. The recirculation length (wake) is considerably shortened as the buoyancy-driven flow strengthens. Even a weak buoyancy-induced flow (for instance, Ri = 1) is sufficient to mar the influence of pulsatile velocity. The Richardson and Prandtl numbers do not influence the phase difference in the growth of the momentum boundary layer. Overall, the improvement in the Nusselt number is significantly lowered by the aiding-buoyancy mixed convection than that in the forced convection regime. While this may seem like a detrimental effect on the overall heat transfer, this offers a potential tool for modulating the rate of heat transfer for the processing of temperature-sensitive materials wherein the main consideration is to limit the maximum temperature in the system. The present results can be used to devise an operating envelope of conditions depending upon the envisaged application. Finally, the mean Nusselt number is correlated by using the modified velocity and viscosity scales accounting for the contribution of the mean flow and the buoyancy-induced flow.

D-Shaped Surface Plasmon Photonic Crystal Fiber Temperature Sensor

A D-shaped photonic crystal fiber (PCF) temperature sensor based on surface plasmon resonance (SPR) with high sensitivity and high figure of merit is presented in this paper. To enhance surface plasmon resonance, the gold film is deposited on the polished flat of D-shaped photonic crystal fiber. Ethanol and chloroform are employed as temperature-sensitive materials, which are placed on the outside of the fiber to detect temperature changes. When the phase-matching condition is met, the core mode couples with the surface plasma mode. The finite element method is used to perform all numerical simulations of sensor characteristics in the COMSOL software. The results show that the highest sensitivity of the sensor can reach 6.36 nm/°C and the maximum figure of merit (FOM) is 0.3440/°C in the range of −5 ~ 60 °C. To our knowledge, the achieved sensing characteristics are significantly better than those of the current PCF temperature sensors. Furthermore, excellent linearity with a polynomial fit R2 as high as 0.9981. The proposed sensor has exceptional performance in terms of temperature detection range, sensitivity, FOM, and fabrication, making it suitable for a wide variety of biochemical and medical applications.

The Cracking Resistance Behavior of Geosynthetics-Reinforced Asphalt Concrete under Lower Temperatures Using Bending Test

Asphalt is a kind of temperature-sensitive material. With the decrease of temperature, the deformation capacity of an asphalt mixture will be significantly reduced. When the temperature is greatly reduced, the asphalt layer will produce large shrinkage tensile stress and strain, resulting in cracking. Therefore, the cracking resistance behavior is essential for the asphalt. In order to study the cracking resistance behavior of geosynthetics-reinforced asphalt under lower temperatures, the bending tests were carried out indoors at a temperature of −10 °C. The results showed that compared with the unreinforced asphalt sample, the flexural tensile strength at failure of the geogrid-reinforced sample was increased by 14.1% and 12.3%, corresponding to AC-13C and AC-20C. Additionally, the geotextile-reinforced sample was reduced by 2.5% and 3.6%, corresponding to AC-13C and AC-20C. The values of the bending stiffness modulus of the geogrid- and geotextile-reinforced samples were reduced by 6% and 1%. The cracking energy of the geogrid-reinforced asphalt provides by 45.2% and 30.8% more than unreinforced asphalt, corresponding to AC-13C and AC-20C. The cracking energy of the geotextile-reinforced asphalt is increased by 4.5% and 0.6% compared with unreinforced asphalt, corresponding to AC-13C and AC-20C. The cracking resistance behavior of geogrid-reinforced asphalt is better than unreinforced and geotextile-reinforced asphalt. The asphalt shows obvious brittleness at a temperature of −10 °C, and the existence of the geosynthetics does not change the shape of the load–deflection curves.

Cold Spray of Nickel-Based Alloy Coating on Cast Iron for Restoration and Surface Enhancement

Cold spray is an emerging additive manufacturing process that allows particles to be coated onto the surface of a base material without melting. It is suitable to repair components made from temperature-sensitive materials, such as grey cast iron, which cannot be easily restored using conventional methods like welding or thermal spray. In this study, the nickel-based alloy Inconel 625 was successfully coated onto a grey cast iron (GJL250) using a cold spray process, and extensive experiments were carried out to study the effects of diffusion between the coating and the substrate after heat treatment at 400, 600, 850 and 1050 °C for 3 and 6 hours durations. The coatings in all conditions were dense (0.25% to 3%) and had defect-free interfaces. Under heat treatment, the diffusion layer increased in thickness with increasing temperature and duration due to atomic diffusion. The Inconel 625 coating is also shown to be effective against oxide growth as compared to grey cast iron. The hardness of the coatings is also stable at high temperatures. The heat-treated coatings at 600 °C achieved a peak hardness of around 500 HV, which is 30% and 60% higher than the as-sprayed coating and grey cast iron substrate, respectively, because of the possible formation of recrystallized nanostructured grains and strengthening precipitates. These findings demonstrate the potential application of using cold spray on nickel-based alloy coatings for restoration and surface enhancement of grey cast iron components, such as engine blocks and pump housings.

Constitutive Model and Recrystallization Mechanism of Mg-8.7Gd-4.18Y-0.42Zr Magnesium Alloy during Hot Deformation.

The hot deformation behavior of Mg-8.7Gd-4.18Y-0.42Zr alloy was investigated by uniaxial hot compression tests at 300–475 °C with strain rates of 0.002–10 s−1. The average activation energy was calculated as 227.67 KJ/mol and a constitutive relation based on the Arrhenius equation was established in this study. The results show that Mg-8.7Gd-4.18Y-0.42Zr magnesium alloy is a strain rate and temperature-sensitive material. When the temperature is constant, the flow stress increases with the increase of strain rate, while when the strain rate is stable, the flow stress decreases with the increase of temperature. DRX is the main softening mechanism of the alloy, including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). Meanwhile, the DRX grains nucleate preferentially at the twin intersections in the parent grains under the deformation condition below 300 °C and gradually expand outward with the increase of strain. When the compression temperature is above 400 °C, DRX grains nucleate preferentially at the original grain boundary and then gradually expand inward with the increase of strain. The optimum deformation conditions of the studied alloy are performed at 400–450 °C and 0.002–0.02 s−1 by a comprehensive comparison of the hot processing map, microstructure refinement, and formability.

Conductive Layers on a Shrinkable PET Film by Flexographic Printing.

In this study, the extremely important and difficult topic of flexographic printing on a heat-shrinkable substrate was taken up. Six commercially available, electrically conductive inks based on silver, copper and graphite nanoparticles were selected and tested upon their applicability for printing on the temperature-sensitive PET material. As a printing substrate, the one-direction heat-shrinkable PET film, with a maximum shrinkage of 78%, was selected. All of the examined inks were subjected to the printing process throughout three different anilox line screens. The tested inks, along with the electric paths printed with them, were subjected to various tests. The main parameters were evaluated, such as printability combined with the rheology tests and ink adhesion to the examined PET substrate together with the electrical conductivity before and after the shrinkage.

Characterization and tuning of anisotropy property of grating structure using electrical method

Anisotropy is an important property used for characterizing objects. It is always analyzed by the conventional optical method. However, the conventional optical method, which used parameters changes for enhancing and adjusting the signals, is ineffective and inconvenient. In this study, a new on-chip electrical approach to characterize the anisotropy of the object was proposed. This approach utilized the electrical signal, photocurrent, to characterize the anisotropy features of the material. This near-field sensing approach can easily tune/enhance the anisotropy signals compared to the conventional far-field optical technique. As a simple and good example, a metal-grating structure was used. To describe the anisotropy property of the object, an electrical anisotropy, η, was introduced. The simulated results demonstrated that the proposed method is as accurate as the conventional optical method. Moreover, the electrical method is also more effective and flexible in adjusting and tuning the anisotropy signals. The most significant enhanced η mode was improved from 26.08% to 92.48%. This work hopefully will inspire more research into the development/integration of the on-chip sensing devices that serve next-generation sensors for biomolecular, chemical, and temperature-sensitive anisotropy materials.

Dual-parameter sensor for simultaneously measuring refractive index and temperature based on no-core fiber and SPR effect

Refractive index and temperature are two basic properties of matter. Therefore, we propose a dual-parameter sensor based on no-core fiber and surface plasmon resonance (SPR). It can simultaneously measure temperature and refractive index. The sensor structure comprises no-core fiber, metal silver, and polydimethylsiloxane (PDMS). Metallic silver is used to excite the SPR effect, and PDMS is a suitable temperature-sensitive material. The silver film is deposited on the bottom of no-core fiber for refractive index measurement. Silver film and PDMS are deposited on the top of no-core fiber for temperature measurement. Numerical results show that refractive index and temperature can be reflected in the same spectrum, and the two parameters do not interfere with each other. This phenomenon improves the efficiency of measurement. In addition, the maximum spectral sensitivities of the sensors are 5200 nm/RIU and 7.2 nm/℃, respectively. The results also show that the sensor's performance is not sensitive to the change in structural parameters, which makes the sensor easy to prepare. Dual parameter measurement and simple structure make the sensor unique. It has good application prospects in biochemical detection, environmental monitoring, medical sensing, and other fields.

Thermal tuning of vibration band gaps in homogenous metamaterial plate

The acoustic metamaterial is a class of artificial structures designed to transmit, prohibit, or trap and amplify vibration waves at certain frequencies by periodically manipulating the physical parameters such as modulus, density and chirality. Compared to the traditional phononic crystals with the fixed configuration of periodic multi-materials or geometric structures, a novel design with homogenous temperature-sensitive material will probably embody the advantages in both fabricability and tunability. To concrete and validate this design concept, a thin plate merely adopting homogenous thermo-sensitive epoxy resin is presented as an illustration in this research. By periodically distributing the heating source in a particular shape, a periodic thermal field can be induced and further naturally elicits a periodic distribution of Young's modulus. The thermal diffusion effect and nearly power-law-decreasing modulus-temperature relation give rise to a concentric circular distribution of Young's modulus, which transforms the homogenous plate into a novel gradient metamaterial plate. The transmitting and prohibiting effect in wave propagation is validated for both longitudinal and bending vibration waves by theoretical modeling and finite element analysis (FEA). Further research shows that the vibration band gaps can be significantly tuned in both frequency and bandwidth by the power density and configuration of the heat source. The longitudinal vibration band gaps indicate attenuation with the larger high-temperature region; nevertheless, the widest bending vibration band gaps are not monotonically changing. Additionally, the frequencies in both vibration modes decrease with the increasing thermal field. This research explores a novel construction concept for the periodic metamaterial plate by homogenous smart material, which may present more possibilities with the development of multi stimulus responsive smart materials and the physical field application technologies in the future.

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.