Wet Interface Research Articles

Surface modification of sepiolite and its application in one-component silicone potting adhesive

Abstract In this study, the utilization of sepiolite (SEP), renowned for its remarkable water absorption capacity, in a one-component silicone potting adhesive was explored to evaluate its impact on the efficacy of tunnel crack injection adhesive. Initially, SEP underwent high-temperature calcination, and X-ray diffraction and thermogravimetric tests were conducted to analyze the influence of calcination on its crystal structure and water-absorption capacity, respectively. Following this, various coupling agents were employed to modify the SEP, and their respective impacts on the performance of the tunnel crack-filling adhesive were investigated. The outcomes revealed that KH550 exhibited the most effective modification. Subsequent analysis delved into the effect of varying the dosage of KH550 on adhesive performance, demonstrating optimal cost-effectiveness at a dosage of 2 phr. Furthermore, a comparative assessment of the adhesive’s performance in wet and dry interfaces revealed that the addition of SEP resulted in comparable bond strength between wet and dry interfaces, indicating minimal influence from the wet interface.

In situ assembly enabling adhesive-free bonding of large area electronic sensors to concrete for structural health monitoring

Abstract Cracks developed in concrete infrastructure are one of the primary mechanisms that degrade their structural integrity, which may result in structural failures. Previous research on soft elastomeric capacitors (SEC) has shown their viability for structural health monitoring of structural materials, including concrete, steel, and fiberglass composites. The SEC, or its derivative version with a corrugated geometry termed corrugated SEC or cSEC, is a parallel plate capacitor. Prior work demonstrated that it was possible to directly paint the electrode interfacing with the structural material onto the structure and adhere the rest of the pre-fabricated sensor onto the wet interface, thereby eliminating the need for a joining epoxy. This demonstration was conducted on steel and fiberglass. The study on concrete was left to future work as concrete exhibits a much rougher surface and structure/sensor capacitive coupling, causing a significant amplification in signal noise. This study advances structural health monitoring in concrete applications by investigating the in situ assembly of the SEC on concrete where the carbon black (CB)-based electrode plate of the cSEC is directly painted onto the concrete surface and serves as both the adhesive and electrode for the sensor. A series of free-vibration and compression tests were designed and conducted to evaluate the sensing performance of in situ assembled cSEC compared to that of an epoxy-bonded cSEC. Additionally, the bonding strength of the in situ assembled and epoxy-bonded cSEC is evaluated through a peel test. Results show good strain sensing capabilities of the in situ assembled SEC with an R 2 value of 0.986 and a resolution of 45 ± μ ε . Even though the epoxied cSEC demonstrated a higher bonding strength than the in situ assembled cSEC, the in situ assembled cSEC demonstrated adequate bonding strength for the application. This research contributes to the scientific understanding of sensor adhesion and opens avenues for practical applications in infrastructure monitoring, potentially leading to more resilient and sustainable urban environments.

Hagfish-inspired hydrogel for root caries: A multifunctional approach including immediate protection, antimicrobial phototherapy, and remineralization

Root caries is the main cause of oral pain and tooth loss in the elderly. Protecting root lesions from environmental disturbances, resisting pathogens, and facilitating remineralization over time are essential for addressing root caries, but are challenging due to the irregular root surface and the complex oral environment. Hagfish secretes slime when facing danger, which converts into gels upon contact with seawater, suffocating the predators. Inspired by hagfish's defense mechanism, a fluid-hydrogel conversion strategy is proposed to establish a mechanical self-regulating multifunctional platform for root caries treatment. The fluid system (silk fibroin-tannic acid-black phosphorene-urea, ST-BP-U), in which urea disrupts the hydrogen bonds between silk fibroin and tannic acid, can easily spread on the irregular root surface and permeate into dentinal tubules. Upon contact with the surrounding water, urea diffuses, prompting the hydrogel re-formation and creating intimate attachments with micromechanical inlay locks. Meanwhile, BP increases the crosslinking of the re-formed hydrogel network, resulting in reinforced cohesion for robust wet adhesion to the tooth root. This process establishes a structured platform for effective antimicrobial phototherapy and dentin remineralization promotion. This water-responsive fluid-hydrogel conversion system adapts to the irregular root surface in the dynamic wet environment, holding promise for addressing root caries. Statement of significanceRoot caries bring a heavy burden to the aging society, but the irregular root surface and dynamic moist oral environment always hinder non-surgical therapeutic effects. Here, we propose a water-responsive fluid-hydrogel conversion strategy aimed at mechanical self-regulation on the irregular and wet root interface to construct a functional structural platform. The liquid system (ST-BP-U) that prebreak intermolecular hydrogen bonds can easily spread on irregular surfaces and dentin tubules. When encountering water, hydrogen bonds re-form, and BP increases the crosslinking of the hydrogel formed in situ. Based on this firm wet-adhesion platform, it provides powerful phototherapy effects and promotes dentin remineralization. This fluid-hydrogel conversion system turns the disadvantages of wet environment into advantages, offering a promising strategy for root caries.

Characterization of leakage signatures in buried water pipes by ground penetrating radar(GPR) and instantaneous frequency analysis

The aging and complexity of underground water pipes pose significant challenges to modern society, necessitating long-term monitoring and maintenance to prevent the socioeconomic costs. So, effective nondestructive and geophysical methods are needed to localize the possible leakage areas before any rational opening up is conducted. In this study, we propose a workflow to generate instantaneous frequency slices (IFS) from raw ground penetrating radar (GPR) data. Characterizing the horizontal and vertical patterns of water leakage using IFS revealed two key mechanisms—reflections due to the dry and wet interface and absorption due to water distributed in soil—that significantly influence instantaneous frequency. A well-designed real site (Q-Leak), in collaboration with the Water Supplies Department (WSD) of the government, was conducted to replicate typical leakage scenarios, validating the effectiveness of our IFS-based approach. The results of proposed method demonstrate that IFS is a reliable approach for characterizing leakages in buried water pipes, effectively addressing several challenges associated with amplitude slice analysis. Our proposed methodology enriches the toolkit available for large-scale, future-oriented water leakage detection.

Identification of force chains in wet coal dust layer and the effect of porosity on three-body contact stiffness

Aiming at the three-body contact problem of mechanical rough surface containing wet coal dust interface, the three-body contact model of rough surface containing wet coal dust interface is constructed by comprehensively considering the contact deformation of rough surface and contact characteristics of wet coal dust, and based on the crushing theory. By analysing the contact force, load-bearing particle size and adjacent contact angle thresholds of the wet coal dust layer, the force chain identification criterion is formulated. Finally, quantitative calculations of the force chain characteristics are performed to reveal the effect of different initial porosities on the three-body contact stiffness, which is verified experimentally. The results of the study show that the average contact force of the wet coal dust layer can be used as the force chain contact force threshold, the average particle size can be used as the force chain particle size threshold, and the force chain angle threshold is determined by the particle coordination number. As the initial porosity decreases, the number, length and stiffness of force chains in the wet coal dust layer increase significantly, and the stiffness reaches a maximum value of 2.007 × 108 pa/m at the moment of downward pressure to stabilisation, while the trend of force chain bending varies in the opposite direction, and its minimum bending degree decreases to 20°. The maximum relative error between the simulation and experimental results of three-body contact stiffness is 9.64%, which proves the accuracy of the force chain identification criterion and the quantitative calculation of three-body contact stiffness by force chain.

Flexible ionic liquid aided “LAGP in PVDF” quasi-solid-state electrolyte for high performance and stable Li metal batteries

The NASICON-type ceramic Li1·5Al0.5Ge1.5(PO4)3 (LAGP) electrolyte has been proposed as the most competitive candidates of electrolyte materials toward solid-state Li metal batteries (LMBs) by reason of its high ionic conductivity, cyclic stability under extreme temperatures and wide voltage window. However, poor interface contact, high interfacial resistance and intractable mechanical properties greatly limit its practical applications. In this work, an inorganic-polymer “LAGP in PVDF” quasi-solid-state electrolyte (QSSE) is developed via solution casting method, in which pyr14TFSI ionic liquid (IL) and LiTFSI are combined as functional wetting interface. Benefiting from the coherent interaction of LAGP nanoparticles incorporated into the polymer matrix, and inherent protection of IL, the overall performance of the optimized QSSE include thermal stability, dense structure, flexibility and electrochemical properties. The XRD, SEM, XPS tests demonstrate that the IL using as a solid/electrolyte modified interlayer can enhance Li+ transport, interfacial infiltration and homogenize lithium deposition. The LiFePO4|PL-25LAGP|Li solid-state battery presents an excellent circulation performance under ambient temperature, which displayed an initial discharge specific capacity of 146.8 mAh g−1 at 0.5C and capacity retention of 96.25 % after 150 cycles. The flexibility PL-LAGP CSE shows superior safety and greater development potential for the “LAGP in PVDF” composite electrolyte in solid state LMBs.

Experimental Study on Flexural Resistance of UHPC Wet Joint Precast Reinforced Concrete Bridge Deck Slabs with Variable Cross-Section

With the convenient and fast requirements for construction in bridge engineering, prefabricated assembly technology is widely applied in engineering construction. Typically, prefabricated bridge decks are connected through cast-in-place wet joints. Wet joints, as the primary load-bearing parts of bridge decks, undergo complex stress and are prone to cracking and damage. Particularly in the negative bending moment region of bridges, the influence of tensile stress on wet joints is more severe, thus enhancing the mechanical performance and crack resistance of joints becomes crucial. This paper investigates the mechanical behavior of prefabricated reinforced concrete bridge deck panels with variable cross-sections under negative bending moments, focusing on the performance of Ultra High-Performance Concrete (UHPC) wet joints. Full-scale experimental tests were conducted on a 176 m steel truss composite continuous rigid bridge, employing C50 concrete panels with UHPC wet joints. Results show three distinct stages: elastic, crack initiation and propagation, and failure. The maximum failure load reached 822 kN, with a maximum displacement of 21.64 mm. Concrete strains indicate compressive stress near the wet joint and tensile stress near the loading positions. Cracks primarily develop at the wet joint interface and propagate under increasing load, ultimately leading to flexural–shear failure near the variable cross-section of the wet joint. Numerical simulations using ABAQUS/CAE (2020) corroborate experimental findings, closely matching load-displacement curves and identifying damage locations. The study demonstrates that UHPC wet joints significantly enhance crack resistance, meeting design requirements for improved mechanical performance in bridge structures subjected to negative bending moments.

A dry polymer nanocomposite transcutaneous electrode for functional electrical stimulation

BackgroundFunctional electrical stimulation (FES) can be used in rehabilitation to aid or improve function in people with paralysis. In clinical settings, it is common practice to use transcutaneous electrodes to apply the electrical stimulation, since they are non-invasive, and can be easily applied and repositioned as necessary. However, the current electrode options available for transcutaneous FES are limited and can have practical disadvantages, such as the need for a wet interface with the skin for better comfort and performance. Hence, we were motivated to develop a dry stimulation electrode which could perform equivalently or better than existing commercially available options.MethodsWe manufactured a thin-film dry polymer nanocomposite electrode, characterized it, and tested its performance for stimulation purposes with thirteen healthy individuals. We compared its functionality in terms of stimulation-induced muscle torque and comfort level against two other types of transcutaneous electrodes: self-adhesive hydrogel and carbon rubber. Each electrode type was also tested using three different stimulators and different intensity levels of stimulation.ResultsWe found the proposed dry polymer nanocomposite electrode to be functional for stimulation, as there was no statistically significant difference between its performance to the other standard electrodes. Namely, the proposed dry electrode had comparable muscle torque generated and comfort level as the self-adhesive hydrogel and carbon rubber electrodes. From all combinations of electrode type and stimulators tested, the dry polymer nanocomposite electrode with the MyndSearch stimulator had the most comfortable average rating.ConclusionsThe dry polymer nanocomposite electrode is a durable and flexible alternative to existing self-adhesive hydrogel and carbon rubber electrodes, which can be used without the addition of a wet interfacing agent (i.e., water or gel) to perform as well as the current electrodes used for stimulation purposes.

Experimental study on crack performance of steel and early-age BFRC composite beams in negative moment region

The wet joint interface concrete deck in the negative moment region of steel-concrete composite beams is susceptible to tensile cracking, which compromises the durability of the structure. Herein, a basalt fiber reinforced concrete (BFRC) is proposed to examine the wet joint cracking performance of concrete deck in the negative moment region of steel-concrete composite beams. To this end, four-point bending tests were conducted on seven steel-concrete composite beams to investigate failure modes, crack distribution patterns, load-deflection relationship, and load-crack width relationship. Experimentally, the effects of the wet joint concrete types (BFRC and normal concrete), basalt fiber volume content (0, 0.3%, and 0.6%), and concrete age (28, 14, 7, and 3 days) on their mechanical behavior were performed and discussed. The results showed that typical flexural failure commonly occurred in all specimens under the negative moment, with initial cracks appearing at the wet joint interface. The wet joint concrete with basalt fiber volume content of 0.3% exhibited the highest crack resistance, which resulted in a higher number of cracks, less crack spacing, and more uniform crack distribution in the wet joint concrete deck. The prediction methods of the average crack spacing and crack width of the wet joint concrete were proposed based on the existing theoretical models. The crack width and concrete age influence coefficients were proposed to rationally assess the effects of basalt fiber and concrete age. The modified formulas for the average crack spacing and crack width showed a reasonably good agreement with the experimental results when considering the effects of basalt fiber and concrete age. These formulas can be effectively utilized to evaluate the main crack width at the non-interface joint in the negative moment region of steel-concrete composite beam decks. The proposed approaches can provide a simple and practical method to effectively predict the crack width in the negative moment region of the steel-concrete composite beam.

Transient and directional growth of supramolecular hydrogels through reaction–diffusion-mediated self-assembly for dynamic wet gluing

The growth of supramolecular structures in biological systems is usually featured by dynamics and directionality, yet remains a real challenge in synthetic scenarios. Here, we show our access to transient and directional growth of supramolecular hydrogels through a simple reaction–diffusion-mediated self-assembly strategy. Transient and directional propagation of acid/base gradients are achieved through the diffusions of acid and base from opposite directions followed by the neutralization reaction at their crossing of diffusional fronts. The propagating distance maxima and lifetimes of the gradients can be easily controlled by changing the contents of acid/base. By coupling pH-sensitive gelators to the reaction–diffusion system, transient and directional growth of supramolecular hydrogels with controlled width maxima and lifetimes is realized. The growing direction of the hydrogel fibers at the microscopic level is demonstrated to be dominated by the gradient strengths of the pH signals and gelators. We further leverage the dynamic and directional gelation at the wet interface of soft hydrogel substrates for a proof-of-concept application of dynamic wet gluing.

Sulfur Dioxide Promoted Mercury Fast Deposition over a Selenite-Chloride-Induced Surface from Wet Flue Gas.

Gaseous elemental mercury (Hg0) extraction from industrial flue gases is undergoing intense research due to its unique properties. Selective adsorption that renders Hg0 to HgO or HgS over metal oxide- or sulfide-based sorbents is a promising method, yet the sorbents are easily poisoned by sulfur dioxide (SO2) and H2O vapor. The Se-Cl intermediate derived from SeO2 and HCl driven by SO2 has been demonstrated to stabilize Hg0. Thus, a surface-induced method was put forward when using γ-Al2O3 supported selenite-chloride (xSeO32--yCl-, named xSe-yCl) for mercury deposition. Results confirmed that under 3000 ppm SO2 and 4% H2O, Se-2Cl exhibited the highest induced adsorption performance at 160 °C and higher humidity can accelerate the induction process. Driven by SO2 under the wet interface, the in situ generated active Se0 has high affinity toward Hg0, and the introduction of Cl- enabled the fast-trapping and stabilization of Hg0 due to its intercalation in the HgSe product. Additionally, the long-time scale-up experiment showed a gradient color change of the Se-2Cl-induced surface, which maintained almost 100% Hg0 removal efficiency over 180 h with a normalized adsorption capacity of 157.26 mg/g. This surface-induced method has the potential for practical application and offers a guideline for reversing the negative effect of SO2 on gaseous pollutant removal.

Microscopic Analysis of the Wetting Morphology and Interfacial Bonding Mechanism of Preoxidised Kovar Alloys with Borosilicate Glass

This paper investigates the wettability of Kovar alloys with high-borosilicate glass and microscopically analyses the mechanism of wettability and diffusion between Kovar and borosilicate glass. First, Kovar was oxidised at 800 °C for 5, 15, 25, 35, and 60 min to observe the oxide morphology of the Kovar surface layer and to analyse the composition of the oxide layer. To investigate the wetting pattern formations of Kovar and high-borosilicate glass under different wetting temperatures, times, and preoxidation conditions, Kovar and high-borosilicate glass obtained from different oxidation treatments were held at 1060 °C for 20 min for wetting experiments, and the glass–metal wetting interface morphology and elemental distribution were observed using SEM and EDS. The elemental diffusion at the wetting interface between the borosilicate glass and the Kovar with different preoxidation and at the glass spreading boundary was investigated. The longitudinal diffusion of the liquid glass in the metal oxide layer formed a new tight chemical bond of Fe2SiO4, and the lateral diffusion of the liquid glass in the Kovar surface layer formed a black halo.

Modularized sulfur storage achieved by 100% space utilization host for high performance lithium-sulfur batteries

Popularization of lithium-sulfur batteries (LSBs) is still hindered by shuttle effect and volume expansion. Herein, a new modularized sulfur storage strategy is proposed to solve above problems and accomplished via employing 100% space utilization host material of cobalt loaded carbon nanoparticles derived from ZIF-67. The modular dispersed storage of sulfur not only greatly increases the proportion of active sulfur, but also inhibits the occurrence of volume expansion. Meanwhile, 100% space utilization host material can greatly improve the conductivity of the cathode, provide a larger electrolyte wetting interface and effectively suppress the shuttle effect. Moreover, loaded cobalt particles have high catalytic activity for electrochemical reaction and can effectively improve the redox kinetics. The cell with new cathode host material carbonized at 650 °C (ZIF-67 (650 °C)) exhibits superior rate performance and can maintain a high specific capacity of 950 mAh/g after 100 cycles at 0.2 C, showing a good cycle stability.

Wetting critical behavior in the quantum Ising model within the framework of Lindblad dissipative dynamics

We investigate the critical behavior, both in space and time, of the wetting interface within the coexistence region around the first-order phase transition of a fully-connected quantum Ising model in slab geometry. For that, we employ the Lindblad master equation formalism in which temperature is inherited by the coupling to a dissipative bath, rather than being a functional parameter as in the conventional Cahn's free energy. Lindblad's approach gives not only access to the dissipative dynamics and steady-state configuration of the quantum wetting interface throughout the whole phase diagram but also shows that the wetting critical behavior can be successfully exploited to characterize the phase diagram as an alternative to the direct evaluation of the free energies of the competing phases.

Exploring a balance between strength and ductility of hexagonal BN nanoplatelet reinforced ZK61 magnesium composite

The practical applications of magnesium (Mg) alloys are usually beset by their relatively low strength and limited ductility. Herein we attempt to fabricate hexagonal BN nanoplatelet (BNNP) reinforced ZK61 magnesium composites using a combination of spark plasma sintering and friction stir processing. The resulting composites exhibit microstructural characteristics of homogeneous dispersion of BNNP in Mg matrix with refined equiaxed grains and (0002) basal texture roughly surrounding the pin column surface. Transmission electron microscopy observation illustrates that trace amounts of Mg3N2 and MgB2 form at BNNP-Mg interface, in which Mg3N2 locates at the basal plane of a BNNP and MgB2 grows at its open edge. The spatial distribution of Mg3N2 and MgB2 facilitates interfacial wetting and stronger BNNP-Mg interface in such a way that interfacial products act as anchors bonding between them. In comparison with monolithic ZK61 alloy, the BNNP/ZK61 composites display simultaneous improvements in yield strength, hardness and ductility, achieving good strength-ductility balance. This research is expected to shed some light on BNNP potentials for designing and producing magnesium composites with high strength and good ductility.

Design and validation of a wheel-rail adhesion simulator in PLS-Circulator

A 1:4 scaled test rig called 'PLS-Circulator' is introduced for wheel-rail contact research under large slip conditions, which is composed of two wheel assemblies, 2 m diameter ring track with sprinklers surrounded, gearbox and two servo motors. On this basis, a wheel-rail adhesion simulator was designed to generate and measure the wheel-rail contact force. The slip ratio is the specific value of two motor speeds, which brings convenience to precisely control. SIMPACK simulation results showed that the slip ratio converged to the target value after the initial time in consideration of gear meshing vibration. The validation of the adhesion recovery was carried out utilizing PLS-Circulator under large slip conditions. Experimental results showed that in both steady and dynamic slip ratio experiments the adhesion coefficient could increase up to 26% from a lower adhesion caused by wet wheel-rail interface at the vehicle velocity of 20 km/h.

Hybrid Interfacial Transition Zone between Wet-On-Wet Casted Concrete-Microstructure and Mechanical Properties.

The manufacture of elements containing two types of concrete allows for the minimization of the amount of Portland cement by matching the properties of concrete with local structural and durability requirements. The most common production method of the hybrid element is wet–on–hard and wet–on–wet. Casting wet–on–dry is the most common approach while casting wet–on–wet has been used mostly for concrete overlays and screeds. The study focuses on the wet–on–wet method but is applied in the production of vertical and horizontal elements. Bond-behavior and micro properties of the wet–on–wet casting interface of ultra–high–performance concrete (UHPC)–normal strength concretes are investigated. The obtained results indicate the formation of a hybrid interfacial transition zone between the two types of casted concrete. The binder matrix located in this zone appeared to combine properties of both used concrete. Porosity, phase composition, and presumably also strength, changed gradually. Furthermore, despite significant differences in shrinkage, no microcracking or delamination was observed in that zone. The ultimate flexural and compressive strength of the produced elements were either equal to the stronger concrete or were higher than the weaker of the used concrete.

Numerical calculation and analysis of mechanical properties of UHPC wet joint interface of prefabricated segmental beams

Prefabricated structure has already become the main body of future building constructions, however, weak shear resistance, joint interface easy to peel and poor durability of diamond wet joint of fabricated segmental beam is throughout a difficult technical problem. In order to solve that, a "干" (Chinese character) UHPC wet joint structure was designed. ABAQUS finite element software was used to analyze the effects of joint structure, joint reinforcement ratio and joint bond surface roughness on the mechanical properties of UHPC wet joint interface. The results shows that the finite element model based on “Traction-Separation” bond surface can better simulate the mechanical properties of wet joint interface of segmental beam. The interface mechanical properties of "干" joint proposed in this paper are significantly better than those of diamond joint; The tangential shear stress concentration area of the interface is much smaller than that of the diamond joint. The maximum peeling displacement of reinforcement and UHPC concrete in the tensile area of positive moment can be reduced by about 83.7 %“ The interfacial bonding normal stress of "干" wet joint does not increase in the same proportion with the increase of reinforcement ratio, and the influence of reinforcement ratio on interfacial tangential shear stress shows a "bimodal" effect. In this paper, the reinforcement ratio of wet joint is recommended to be 4.8 %; Reinforcement ratio and interface roughness have little effect on the normal peeling displacement of wet joint interface, which can be ignored. China's “Code for design of concrete structures” considers the main shear action of stirrups in the structure, and its calculation results are the closest to the bonding shear strength of the concrete interface of this model.

Wet Interface Engineering for At-rest Sweat Analysis

Wet Interface Engineering for At-rest Sweat Analysis

On-skin paintable biogel for long-term high-fidelity electroencephalogram recording.

Long-term high-fidelity electroencephalogram (EEG) recordings are critical for clinical and brain science applications. Conductive liquid-like or solid-like wet interface materials have been conventionally used as reliable interfaces for EEG recording. However, because of their simplex liquid or solid phase, electrodes with them as interfaces confront inadequate dynamic adaptability to hairy scalp, which makes it challenging to maintain stable and efficient contact of electrodes with scalp for long-term EEG recording. Here, we develop an on-skin paintable conductive biogel that shows temperature-controlled reversible fluid-gel transition to address the abovementioned limitation. This phase transition endows the biogel with unique on-skin paintability and in situ gelatinization, establishing conformal contact and dynamic compliance of electrodes with hairy scalp. The biogel is demonstrated as an efficient interface for long-term high-quality EEG recording over several days and for the high-performance capture and classification of evoked potentials. The paintable biogel offers a biocompatible and long-term reliable interface for EEG-based systems.