Temperature-sensitive Materials Research Articles

Preparation and Experimental Research of Temperature Sensitive Expansion Gel Material for Fire Prevention and Extinguishing in Coal Mines

ABSTRACT In order to solve the problems of high viscosity at room temperature, easy dehydration and shrinkage of phase change gel, and poor plugging effect of traditional mine gel, a new type of temperature-sensitive expansion gel was developed by using hydroxypropyl methyl cellulose, chitosan, guar gum and sodium bicarbonate as raw materials, using orthogonal test and response surface analysis. The structural characterization, characteristics, fire prevention, and extinguishing performance of the temperature-sensitive expansion gel were tested. The experimental results show that the optimal ratio of temperature-sensitive swelling gel is 0.75 wt % chitosan, 0.5 wt % acetic acid, 2.5 wt % hydroxypropyl methyl cellulose, 0.4 wt % sodium bicarbonate, and 0.15 wt % guar gum. The phase transition temperature (LCST) of this ratio is 67°C. After standing at room temperature for 6 h, the gel viscosity is 5852 mpa·s, the expansion ratio is 0.846, and the strength is 319.525 N/m2. During the heating process of the coal sample after adding the temperature-sensitive expansion gel, the gel will undergo phase change and expansion in the high-temperature area of the coal, and the viscosity will increase. It can stay in the high-temperature area, wrap the coal block, and isolate the oxygen from entering, thus effectively inhibiting the coal spontaneous combustion process. In addition, the gel also produces inert gas carbon dioxide, which effectively suffocates the flame. Therefore, compared with the conventional inhibitor solution, the temperature-sensitive expansion gel has better fire extinguishing effect.

Low-temperature strain-free encapsulation for perovskite solar cells and modules passing multifaceted accelerated ageing tests

Perovskite solar cells promise to be part of the future portfolio of photovoltaic technologies, but their instability is slow down their commercialization. Major stability assessments have been recently achieved but reliable accelerated ageing tests on beyond small-area cells are still poor. Here, we report an industrial encapsulation process based on the lamination of highly viscoelastic semi-solid/highly viscous liquid adhesive atop the perovskite solar cells and modules. Our encapsulant reduces the thermomechanical stresses at the encapsulant/rear electrode interface. The addition of thermally conductive two-dimensional hexagonal boron nitride into the polymeric matrix improves the barrier and thermal management properties of the encapsulant. Without any edge sealant, encapsulated devices withstood multifaceted accelerated ageing tests, retaining >80% of their initial efficiency. Our encapsulation is applicable to the most established cell configurations (direct/inverted, mesoscopic/planar), even with temperature-sensitive materials, and extended to semi-transparent cells for building-integrated photovoltaics and Internet of Things systems.

Stabilizing a low temperature phase change material based on Glaubers salt

The aim of this research is to enhance the performance of Glauber's salt (sodium sulfate decahydrate, SSD) as a phase change material (PCM) for thermal energy storage applications, as well as for shipping of temperature-sensitive materials. The study investigates the effects of modifying SSD with potassium chloride (KCl) and ammonium chloride (NH4Cl) to achieve lower phase transition temperatures of between +6 °C and + 13 °C. Sodium polyacrylate (PAAS) is employed as a thickening agent to prevent phase separation, and borax is used as a nucleating agent to suppress supercooling. Various ratios of KCl:NH4Cl are tested, and the impact of PAAS concentration on phase segregation is explored. The results show that a 2 wt% concentration of PAAS effectively prevents phase separation. Samples with a KCl:NH4Cl ratio of 1:1.83 exhibit stable phase transition behavior and maintain latent heat values within the range of 130–140 J/g after 30 thermal cycles. Maintaining a total KCl and NH4Cl proportion of 10 wt% is crucial to achieve the desired lower melting temperature. The study highlights the significance of thermal cycling in improving the stability of the PCM. The optimized SSD-based eutectic PCM formulations hold promise for applications in the cold chain industry.

3D nonlinear finite element investigation of laminated bamboo plate strengthened prestressed concrete slab

Due to environment and recycling concerns, interest in applying natural fiber reinforced polymer (NFRP) as an alternative for glass/carbon FRP to strengthen concrete structures has been increasing. This study developed a 3D nonlinear finite element (FE) model for laminated bamboo (LB) plate strengthened prestressed concrete slab. By involving temperature load on defined temperature sensitive material, the proposed model provided good simulation of prestressing process. The accuracy of the developed model was confirmed through comparisons with experimental data, representing peak load discrepancies of only 6.5% and 8.2% for un-strengthened and strengthened slabs, respectively. The parametric study examined the impact of LB plate dimensions and tensile strength, alongside the use of FRP wraps, on concrete slab performance. The results show that the 15 mm thick LB plate can enhance the slab’s peak load by 83.2%. Variations in LB plate tensile strength by up to 10% do not significantly affect the performance of the strengthened prestressed concrete. The increases of the peak load for strengthened cases with LB plate width of 150 mm, 300 mm and 460 mm were 29.4%, 41.9% and 50.2%, respectively. It also shows that FRP end wraps can increase the performance of thick LB plate strengthened prestressed concrete slab.

Morphology changes of polymer solid-solid phase change material in high-viscosity modified asphalt (HVMA) and its influence on the properties of HVMA

Asphalt pavement has excellent performance, but the asphalt binder is a temperature-sensitive material, which not only easily causes high-temperature distress, but also exacerbates the “urban heat island effect”. One possible method to solve this problem is to use phase change material (PCM) in the asphalt mixture, in which polymer solid-solid phase change material (PSSPCM) is one of widely used PCM. If the PSSPCM can be used in high-viscosity modified asphalt (HVMA), the high-performance modified asphalt with temperature regulation function can be obtained. However, the morphology of PSSPCM may change under the high mixing temperature of HVMA, which may also influence the properties of PSSPCM/HVMA composite. This paper selected one typical PSSPCM to investigate the morphology changes of solid-solid phase change material in HVMA and its influence on the properties of HVMA. The change of morphological and thermal property of PSSPCM in the high-temperature preparation were characterized by scanning calorimeter tests, thermogravimetric tests and heating tests, the physical, rheological and temperature regulation properties of PSSPCM/HVMA were also investigated. Test result shows that, the PSSPCM melted in HVMA at high mixing temperatures condition. However, when added in smaller contents of PSSPCM, the melted PSSPCM could uniformly distribute in the HVMA and the polymer network structure was formed. The melted and distributed PSSPCM in HVMA still had favorable temperature regulation function. The temperature regulation range of PSSPCM during the heating process and cooling process is maximum 3.8°C and 2.9°C respectively. Notably, the PSSPCM/HVMA has great high-temperature properties and favorable low-temperature properties. This study has reference value for developing the high-performance modified asphalt with temperature regulation function.

Temperature-assisted electromagnetic surface modes in graphene-based temperature sensitive metafilms

Graphene has the potential to manipulate surface modes in frequency bands from THz to mid-IR regions. Typically, due to single-atom thickness and low charge-carrier density, the thermal response of graphene is ineffective. Temperature-sensitive materials (TSMs) can play an active role in enhancing the thermal response of graphene-based devices. In the present work, graphene-based temperature-sensitive metafilms have been proposed for thermally tunable propagation of electromagnetic surface modes. A detailed analytical and numerical solution for temperature-dependent electromagnetic surface (even and odd) modes supported by the graphene-based temperature-sensitive metafilm has been studied. The Kubo’s formulation has been used to model optical conductivity (σ g ) while the hybrid Drude’s model is implemented to realize the indium antimonide (InSb) as temperature-sensitive material. To simulate the metafilm, the waveguide modal analysis approach was implemented, while the realization of the graphene sheets was achieved by the use of impedance boundary conditions (IBCs). The propagation characteristics for even/odd surface modes were analyzed under different values of temperature (T), chemical potential (µ c ), and thickness of metafilm (d). Further, the numerical results for even and odd surface modes under two phases of InSb [Insulator phase (T = 200 K) and metallic phase (T = 300 K)] were compared under different values of chemical potential (µ c ) and TSM film thickness (d). It is concluded that the propagation characteristics of surface modes are sensitive to the external temperature and can be tailored by tuning the temperature, chemical potential (µ c ), and TSM film thickness (d). Moreover, the degeneracy of the even and odd modes can be controlled by varying the temperature and TSM film thickness. The work is suitable for designing temperature-assisted dual channel waveguides, THz optical switches, THz optical logic designs, and flexible thermal-optical sensors.

Ultra-sensitive fiber-optic temperature sensor based on UV glue-based FPI and Vernier effect

In this paper, compact cascaded Fabry-Perot interferometers (FPI) for fiber-optic temperature sensors are proposed and verified. The sensors are prepared by combining the properties of temperature-sensitive material ultraviolet glue (UV glue) and the basic principle of the traditional Vernier effect (TVE), first-order harmonic Vernier effect (HVE), and second-order HVE. The sensing cavity FPIs is made up of UV glue filling the gap between two single-mode fibers (SMF) with flat cut ends. The reference cavity FPIr is composed of SMF-capillary-SMF structure. The temperature sensitivity of the FPIs is up to 1.01 nm/°C by the high thermal expansion coefficient of the UV glue. By changing the free spectral range (FSR) of the FPIr, high detection sensitivities achieved are −10.14 nm/°C, 15.22 nm/°C, and 22.24 nm/°C, corresponding the situation of TVE, first-order HVE, and second-order HVE, respectively. The experimental results indicate that temperature sensors based on UV glue possess a simple and compact structure and strong resistance to electromagnetic interference, making them suitable for temperature measurement in various environments.

Temperature-Sensitive Materials for Oil and Gas Drilling Applications.

With the vigorous development of the petroleum industry, improving the efficiency of oil and gas exploitation has become an important issue. Temperature-sensitive materials show great potential for application in the development and production of oil and gas fields due to their unique temperature-responsive properties. This paper reviews the application of temperature-sensitive materials in oil and gas drilling and introduces the characteristics of three types of temperature-sensitive materials: N-substituted acrylamide polymers, amphiphilic block copolymers, and peptides. Because these materials can change their physical state at specific temperatures, this paper discusses in detail the role of various temperature-sensitive materials as plugging agent, thickener, oil displacing agent, flocculant, and tackifier in oil and gas field operations, as well as the mechanism of action and performance of temperature-sensitive materials in practical oil and gas drilling operations. As we have not yet seen relevant similar literature, this paper aims to discuss the innovative application of temperature-sensitive materials in the oil and gas drilling process, and at the same time points out the problems in the current research and applications as well as future development directions. Through analysis and comparison, we provide an efficient and environmentally friendly materials selection option for the petroleum industry in order to promote the progress and sustainable development of oil and gas extraction processes.

On-line temperature-responsive restricted access material of sample preparation technique coupling with liquid chromatography for detection of tetracycline residues in milk

Effort of sample preparation has been working towards the automation and improvement of accuracy. Development of on-line sample preparation coupled with liquid chromatography (LC) is a promising way. In this study, an on-line extraction-LC automated analysis was proposed based on a temperature-sensitive restricted access material (RAM) for the determination of tetracycline residues (TCs) in milk. The RAM was synthesized using silica as substrate by the two-step surface initiated-atom transfer polymerization (SI-ATRP), styrene (St), sodium 4-vinylbenzenesulfonate (Nass) and a lower critical solution temperature (LCST)-responsive n-vinylcaprolactam (VCl) were conjugated to fabricate multiple interaction-adsorption sites of P(St-co-Nass-co-VCl) on silica interior, while an upper critical solution temperature (UCST)-responsive sulfobetaine methacrylate (SBMA) was then block polymerized to form zwitterionic exclusion sites on exterior. Thereafter, the RAM was packed as extraction column to be fixed into LC ahead of C18 analytical column, establishing automatic analysis by rotation of switching valve. In conjunction with LCST and UCST dual-responsive properties to adjust the hydrophobic-hydrophilic transition of the grafted P(St-co-Nass-co-VCl)-b-PSBMA chains, the RAM column acquires the best extraction of TCs and meanwhile the furthest removal of proteins at about 30 ℃ of column temperature. And using the proposed automatic analysis for monitoring of TCs in milk, a wide linearity (20–900 ng mL−1), low limit of detection (1.0 ng mL−1) and limit of quantification (2.5 ng mL−1) as well as good inter-day (<3.9 % RSD) and intra-day precision (<4.8 % RSD) with satisfactory recoveries (97.2–101.9 %) show the superior efficiency. It is believed that the introduction of temperature-sensitive RAM to construct on-line extraction is a powerful tool for detecting trace substances in scientific analyses.

Benchtop Nickel Catalysis Invigorated by Electron-Deficient Diene Ligands.

ConspectusDue to the rarity of precious metals like palladium, nickel catalysis is becoming an increasingly important player in organic synthesis, especially for the formation of bonds with sp3-hybridized carbon centers. Traditionally, catalytic processes involving active Ni(0) species have relied on Ni(COD)2 or in situ reduction of Ni(II) salts. However, Ni(COD)2 is an air- and temperature-sensitive material that requires use in an inert-atmosphere glovebox, and in situ reduction protocols of Ni(II) salts using metallic or organometallic reductants add additional complications to reaction development.This Account chronicles the development of air-stable Ni(0) precursors as replacements for Ni(COD)2 or in situ reduction. Based on Schrauzer's seminal discovery of Ni(COD)(DQ) as an air-stable zerovalent organonickel complex, our research laboratories at Scripps Research and Bristol Myers Squibb have developed a class of precatalysts based on the Ni(COD)(EDD) (EDD = electron-deficient diene) framework, relying on the steric and electronic properties of the supporting diene to render the metal center stable to air, moisture, and even silica gel but reactive to ligand substitution and redox changes.The stable Ni(0) complexes can be accessed through ligand exchange with Ni(COD)2, through reduction of Ni(acac)2 using DIBAL-H, or electrochemically via cathodic reduction of Ni(acac)2 to Ni(COD)2, followed by addition of an EDD ligand in one pot. As a toolkit, the complexes demonstrate reactivity that is equivalent or enhanced compared to Ni(COD)2, catalyzing C-C and C-N cross-couplings, Miyaura borylations, C-H activations, and other transformations. Since the initial report on Ni(COD)(DQ), its reactivity in C(sp2)-CN activation, metallophotoredox, and electric field-induced cross-coupling have also been demonstrated.By incorporating the precatalyst toolkit into reaction discovery campaigns, our laboratories have been able to perform C(sp3)-S(alkyl) couplings and metallonitrenoid carboamination, both of which represent challenging transformations that were inaccessible with traditional phosphine, nitrogen, or electron-deficient olefin ligands. Computational and experimental studies demonstrate how the quinone ligands are hemilabile, adopting η1(O)-bound geometries to relieve steric strain or stabilize transition states and intermediates; redox-active, able to transiently oxidize the metal center; and electron-withdrawing or -donating, depending on metal oxidation state and coordination geometry. These studies show how the ligands enable key steps in catalysis beyond imparting air-stability.Since our report documenting the catalytic activity of Ni(COD)(DQ), many other laboratories have also observed unique reactivity with this precatalyst. Ni(COD)(DQ) was found to offer superior reactivity to Ni(COD)2 in C-N cross coupling to form N,N-diaryl sulfonamides and in preparation of biaryls from aryl halides and benzene through a Ni-mediated, base-assisted homolytic aromatic substitution.

Boosted hydrophobic properties of leather surfaces by atmospheric pressure plasma brush reactor

In this article, we demonstrate the application of an atmospheric pressure plasma brush (APPB) reactor for improving the hydrophobic properties of leather surfaces treated with organo-silane precursors for the first time. A comprehensive investigation was conducted to analyze the influence of various process parameters, including plasma access current, treatment duration, nozzle height, and gas flow rate, on the observed outcomes effects. The dispersion of active particles in the APPB was scrutinized using an Optical Emission Spectrometer (OES), while the underlying reaction mechanism was elucidated through the integration of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), cross-sectional Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM) analysis. The findings unveiled that the resultant polysiloxane polymers bestowed a remarkable degree of hydrophobicity upon the leather, persisting steadfastly even following a 90-day aging period (WCA >140°). This APPB treatment combined with organosilane strategy may open a new design avenue for the development of surface treatments for intricate and temperature-sensitive substrates materials.

Color-tunable luminescence and temperature sensing properties of Bi3+/Sm3+ or Bi3+/Eu3+ codoped Ba2Gd2Ge4O13 phosphors.

Novel temperature-sensitive luminescent materials, Ba2Gd2Ge4O13 doped with Bi3+, Bi3+/Sm3+ or Bi3+/Eu3+ ions, have been prepared using a conventional solid-state reaction technique. The XRPD study has verified that all the synthesized germanates crystallize in the monoclinic system (space group C2/c, Z = 4). The crystal lattice of the compounds consists of zigzag chains of edge-sharing Me2O7 (Me = Bi3+, Eu3+ or Sm3+) dimers, [Ge4O13] units, and ten-coordinated Ba atoms. Under UV excitation the powders exhibit the luminescence corresponding to the 3P1 → 1S0 (310-550 nm) transition in Bi3+ and 4G5/2 → 6HJ (550-730 nm) in Sm3+ or 5D0 → 7FJ (570-720 nm) transitions in Eu3+ ions. Heating of Ba2Gd1.94Bi0.01Sm0.05Ge4O13 and Ba2Gd1.89Bi0.01Eu0.1Ge4O13 phosphors leads to an irregular decrease in the intensity of the main emission lines. It has been found that the fluorescence intensity ratio between a wide band in the 310-530 nm region and peaks at longer wavelengths may be successfully used as a temperature-dependent characteristic. Absolute/relative sensitivity values for Ba2Gd1.94Bi0.01Sm0.05Ge4O13 and Ba2Gd1.89Bi0.01Eu0.1Ge4O13 germanates reach 0.19% K-1/0.80% K-1 and 2.21% K-1/0.58% K-1, respectively. The above parameters indicate that Ba2Gd2Ge4O13:Bi3+/Sm3+ or Bi3+/Eu3+ samples can be used as potential luminescent materials for non-contact temperature measurement.

Photonic post-processing of a multi-material transparent conductive electrode architecture for optoelectronic device integration.

Emerging flexible optoelectronic devices require multi-material processing capabilities to fully enable the use of temperature-sensitive substrates and materials. This report demonstrates how photonic sintering enables the processing of materials with very different properties. For example, charge carrier transport/blocking metal-oxides, and transparent conductive silver nanowire-based electrodes ought to be compatible with low-energy and high-throughput processing for integration onto flexible low-temperature substrates. Compared to traditional post-processing methods, we show a rapid fabrication route yielding highly-stable hybrid electrode architectures on polyethylene terephthalate (PET). This architecture consists of an interconnected silver nanowire network encapsulated with a thin crystalline photo-sensitive titanium dioxide (TiO2) coating, allowing both layers to be treated using independent photonic post-processing sintering steps. The first step sinters the nanowires, while the second completes the conversion of the top metal-oxide layer from amorphous to crystalline TiO2. This approach improves on the fabrication speed compared to oven processing, while delivering optical and electrical characteristics comparable to the state of the art. Optimized transparency values reach 85% with haze values down-to 7% at 550 nm, while maintaining a sheet resistance of 18.1 Ω sq.-1. However, this hybrid architecture provides a much stronger resilience to degradation, which we demonstrate through exposure to harsh plasma conditions. In summary, this study shows how carefully-optimized photonic curing post-processing can provide more-stable hybrid architectures while using a multi-material processing technique suitable for high-volume manufacturing on low-temperature substrates.

Recent Developments in Low Temperature Wafer Level Metal Bonding for Heterogenous Integration

The low temperature metal bonding processes (<200°C) are attractive methods for novel applications in 3D packaging with simultaneous formation of electrical interconnections and hermetic encapsulation for microelectromechanical systems.Metal wafer bonding is a generic category of processes consisting of various sub-categories, each one defined by the different principles governing the process. One can differentiate between eutectic wafer bonding (a eutectic bonding layer is formed during process by liquid-solid interdiffusion), intermetallic bonding (an intermetallic alloy is formed as bonding layer during the process by solid-liquid interdiffusion, process known also as Solid Liquid Intermetallic Diffusion – SLID or Transient Liquid Phase – TLP), and metal thermo-compression (TC) wafer bonding.The bonding temperature range for the two types of processes showing liquid interface is relatively narrow (<10-20°C) while for metal TC the bonding temperature range is quite broad (~200°). This important parameter is differentiating the focus in studying the processes: for the low temperature eutectic and SLID/TLP the focus is primarily on the development of new materials systems and secondary on process optimization, while for metal TC the focus is equally shared between metal layers optimization (e.g. fabrication method, oxide management) and process optimization.The SLID bonding process studies were focusing on the Cu–In–Sn, Au–In and Bi–In material systems. It was demonstrated that electrical interconnections can be fabricated at bonding temperatures as low as 150°C by taking advantage of the Cu–In–Sn ternary system. The low processing temperatures allow for bonding of temperature sensitive materials and of materials with dissimilar thermo-mechanical properties by thermally induced stress management. Microstructural characterization confirmed the high bonding quality with low amount of defects in interconnections composed of a layered Cu / intermetallic / Cu structure, with a single-phase intermetallic Cu6(Sn,In)5 phase. Moreover, the mechanical testing shows that the bonds have tensile strength above 30 MPa.Au–In SLID bonding can be performed at temperatures slightly higher than the In melting temperature of 156°C. Successful bonds were demonstrated at 180°C. The resulting intermetallic bonding layer has a remelting temperature >450°C and a high shear strength above 30 MPa both at room temperature and 300°C.Another system studied was Au–In–Bi, utilizing the low eutectic point of In–Bi (72oC). Bonds at temperatures of 90 °C were proven. However, in order to consume the various In–Bi intermetallics with low melting temperatures (T< 110 oC), a bonding temperature higher than 110 oC should be used for a reliable result. We have demonstrated such SLID bonds at 115 oC, with a bond line consisting of Au / Au–In IMCs / Au, with Bi inclusions. All these materials have melting temperatures > 271 oC, with the bonding layer being stable at 450 oC if Bi does not form continuous structures.The study of metal TC bonding is reporting recent developments on the optimization of Cu-Cu and Al-Al wafer bonding. To decrease the bonding temperature of Cu-Cu TC bonding, Cu layers fabrication and oxide management are essential. By using certain surface pre-treatment methods such as plasma and self-assembled monolayer (SAM), Cu-Cu low temperature bonding was investigated. Various plasma concentrations were used to investigate the influence of plasma composition on bond strength.Further investigations were performed on the impact of different morphological Cu-properties and their effects on the bonding yield. The comparison of the interdiffusion behavior of layers deposited using different methods (e.g. physical vapor deposition - PVD Cu vs. electroplated - ECD Cu), as well as different surface preparation methods is being reported here. Different surface treatments like in-situ and ex-situ oxide management, as well as pre-bond CMP processes were tested in combination with the respective deposition methods. By combining the most effective sample and process parameters, the necessary bonding temperature for a successful Cu-Cu TC bonding could be reduced to temperatures of 175°C. The successful interdiffusion behavior at such low temperatures was confirmed by cross section TEM measurements.Apart from Cu, Aluminum is widely used material, due to its good electrical conductivity and compatibility with CMOS processes. Aluminum has a very stable native oxide and therefore high temperature and pressure are necessary to generate a successful Al-Al bond at wafer-level. The low temperature Al-Al TC bonding using a thin Palladium passivation layer at 350°C is reported here. The thermo-compression bonding was performed on both blank and patterned wafers.This work is reviewing recent achievements in the reduction of metal wafer bonding process temperature to less than 200°C based on the mechanical, structural and electrical characterization of the metal bonding layers.

Preparation of Temperature-Sensitive Colour-Changing Materials and Their Applications to Clothing Fabrics: Taking a Compound Composed of Crystal Violet Lactone, Bisphenol A, and Octadecanol as an Example

A compound was prepared using crystal violet lactone, bisphenol A, and octadecanol. An in-situ polymerization method was used to prepare temperature-sensitive colour-changing microcapsules. It was printed on fabrics using printing technology. The colour-changing performance of the composite material, thermal weight changes of the microcapsules, and properties of the fabric coated with microcapsules were analyzed using cases. Printed fabric properties of colour fastness to washing, rubbing, strength and colour strength (K/S) were measured in terms of binder (%), a crosslinking agent (%), and temperature variations. The results indicated that the compound gradually changed from purple to blue within the temperature range of 3 °C to 60 °C and eventually faded into a colourless state. The weight of the microcapsule powder decreased as the temperature rose, with no significant change in weight before reaching 100 °C. Between 100 °C and 200 °C, there was a rapid decrease in weight, followed by a slow decrease between 200 °C and 350 °C. After reaching 350 °C, the weight tended to stabilize. When the mass fraction of the cross-linker was 3%, the mass fraction of the binder was 25%, and the baking temperature was 120 °C, the colour fastness, fabric strength, and K/S value (colour intensity) of the cotton fabric coated with microcapsules were optimal.

A three-dimensional force/temperature composite flexible sensor

Flexible sensors that mimic human tactile perception are widely used in areas such as smart prosthetics and human-robot interaction, and play a key role in bridging the gap between humans, robots and the environment. The development of tactile sensors with versatile tactile sensing capabilities remains a challenge. In this paper, a three-dimensional force/temperature composite flexible sensor is proposed and developed. The upper part of the sensor is a temperature-sensitive unit completely covered with a hardened layer, which not only protects the temperature-sensitive material, but also reduces pressure interference. The lower part contains a truncated pyramid bump and four arrays of pressure-sensitive units to achieve three-dimensional force detection. When a three-dimensional force is applied on the sensor, four pressure-sensitive units undergo different resistance changes by which normal and shear components of the force can be decoupled. The temperature-sensitive unit is made of graphene/carbon nanotubes/silicone rubber (GR/CNT/SR) conductive nanocomposite and the pressure-sensitive units are made of graphene/silver nanoflakes/silicone rubber (GR/AgNF/SR) conductive nanocomposite. Experimental results show that force sensitivities of the sensor in x-, y- and z- directions are 1.694 N/V, 1.436 V/N and 0.435 N/V in the ranges of − 1.2–1.2 N, − 1.2–1.2 N and 0–7 N, respectively. The temperature sensitivity is 0.067 V/°C in the range of 25–90 °C. In addition, the sensor was mounted on a manipulator for daily grasping and results demonstrate good application potential.

An in-fiber sensor for simultaneous measurement of cholesterol concentration and temperature based on SPR and MMI

In this paper, we design an in-fiber two-parameter sensor with multimode fiber (MMF)-Au film coated hollow fiber (HCF)-MMF structure, which can simultaneously excite Surface Plasmon Resonance (SPR) effect and Multimode Interference (MMI) effect. A composite material of Au nanoparticles/β-cyclodextrin (AuNPs/β-CD) is deposited on the surface of the Au film coated HCF to realize highly-sensitive measurement of cholesterol concentration. Here, the AuNPs can not only enhance the measurement sensitivity of the SPR sensor, but also increase the numbers of combination sites of β-CD and cholesterol. Then, to solve the cross-sensitivity problem between temperature and cholesterol, the glycerin is selected as a temperature-sensitive material to fill into the inner channel of the HCF, making the MMI sensor sensitive to temperature, and finally realizing the simultaneous measurement of cholesterol concentration and temperature. The experimental results demonstrate that the wavelength shift of the SPR and the MMI are 12.7 nm and 7.9 nm, respectively, when the cholesterol concentration changes from 0 to 500 nM. The temperature sensitivity of the SPR and the MMI are −0.9 nm/°C and 2.64 nm/°C, respectively, in the temperature range of 30°C–46 °C. In addition, the sensor shows good recognition ability of cholesterol molecules in serum environment, with good stability, selectivity and repeatability, and has broad application prospects in the biomedical field.

Layer combination design and effect evaluation of phase change cooling asphalt pavement

Asphalt mixture is a temperature sensitive material. With the change of external environment temperature, asphalt pavement is prone to temperature-related diseases. Adding phase change material (PCM) to asphalt pavement to adjust pavement temperature is one of the effective methods at present. At present, there are many types of research on PCMs, but the research on PCMs added to the pavement structure is very scarce. In this paper, through the temperature test of rutting plate specimens with different layer combinations, the cooling effect of pavement structure combinations with PCMs added to different layers (upper layer, middle layer, and bottom layer) in pavement structure under different illumination times are discussed. Through the self-designed environmental simulation box, the real-time monitoring of the temperature of different layers in the pavement structure is realized. The cooling effect between different layers in different phase change pavement structure combinations is analyzed, and compared with each layer of ordinary pavement structure, and the best addition method is obtained for phase change materials, which provides a certain reference for the construction and specific application of PCM asphalt pavement, and made important contributions to the development of asphalt cooling pavement. The results show that the PCM can effectively reduce the temperature of each layer of the pavement structure. Under different illumination durations, the cooling effect of the samples with PCM in the upper layer was the worst. The samples with phase change material in the middle layer had the best cooling effect in the upper and middle layers of the pavement. The addition of phase change material to both the upper and middle layers had the most obvious cooling effect on the lower layer of the pavement. Therefore, combined with the comprehensive consideration of economy and cooling effect, the comprehensive cooling effect of adding PCMs to the middle surface layer is the best. It is recommended to add phase change materials to the middle surface layer during asphalt cooling pavement construction.

Transparent core-sheath composite fibers as flexible temperature sensor based on liquid crystal color change for smart sportswear

The characteristic of color changes in response to external temperature stimuli has made thermochromic fibers a subject of widespread research interest. However, for practical applications, improvements are still needed in terms of color rendering and the prevention of temperature-sensitive material leakage. This study utilized an optimized thermally induced coaxial dry spinning process to prepare a transparent temperature sensing fiber (PCCF) with a core-sheath structure. The sheath layer and the core layer of the PCCF were polydimethylsiloxane (PDMS) and cholesteric liquid crystal (CLC), respectively. The high transmittance exhibited by PCCF was attributed to the pellucid PDMS, which quickly cured in oil bath to form a complete core-sheath structure. The research results indicated that PCCF displayed uniform morphology (average diameter ∼539 μm), excellent tensile properties (elongation at break up to 183 %), as well as good mechanical, thermal, and sweat resistance stability. In addition, the PCCF showed a colorful variation of hues including yellow, green, blue and purple at a very narrow temperature change from 34 °C to 38 °C, attributing to that the molecular pitch was altered to selectively reflect visible light when the CLC was stimulated by temperature. Meanwhile, high sensitivity and short response time were obtained. When the PCCF was directly integrated into sportswear, the remarkable color changes could be observed as the wearer's body temperature increases. PCCF demonstrates a great potential application in smart sportswear and healthcare area.

Temperature sensing technique across a wide range using phosphorescence intensity ratio of Dy3+-Doped YAG/YAP

To address the need for precise temperature measurement across an extended temperature range, we successfully synthesized a temperature-sensitive phosphorescent material using a high-temperature solid-state method. This material involves the incorporation of dysprosium dopant into the yttrium aluminum garnet/yttrium aluminum perovskite (YAG/YAP) phosphor matrix. Our primary objective was to leverage the phosphorescence intensity ratio of Dy3+ energy level transitions (4F9/2 → 6H15/2, 4I15/2 → 6H15/2) in response to temperature fluctuations, enabling temperature measurements within the 100–1300 °C range. Throughout our investigation, we observed shifts in the peak wavelengths “a” and “b” attributable to thermally coupled energy level transitions as temperature increased. Specifically, at 1000 °C, the peak wavelength “a” shifted from 457.4 nm to 457.8 nm, while at 750 °C, peak wavelength “b” shifted from 497.6 nm to 497.2 nm. Subsequently, we assessed the temperature sensitivity and measurement error of the sample. Impressively, the temperature sensitivity remained consistent across various single-pulse excitation powers and even after 50 h of continuous operation. The maximum absolute sensitivity exceeded 11.21 × 10−4 °C−1, and the relative sensitivity surpassed 2.78 × 10−2 %°C−1. The minimum temperature measurement error was approximately ±2 °C. As a result, the phosphorescent YAG/YAP: Dy3+ powder demonstrates significant potential for applications within the 100–1300 °C temperature range.