Dry Adhesives Research Articles

A high-strength, environmental-friendly, and multifunctional soy protein adhesive inspired by biomineralization

Soy protein is an economical and eco-friendly adhesive material that offers significant potential for the development of bio-based adhesives. However, they have poor water resistance, low bonding strength, mold-susceptibility, and deterioration, which are serious challenges to the widespread application of soy protein adhesives in plywood. This work was inspired by the biomineralization phenomenon and the preparation of a novel soy protein adhesive (SPI-RGT-AgNPs). The SPI-RGT-AgNPs adhesive exhibited excellent viscosity, residual rate, and moisture absorption performance compared with the original soy protein isolate (SPI) adhesive, with an increase from 37° (SPI) to 81° (SPI-10RGT-10AgNPs) in water contact angle testing. The dry and wet adhesion strengths reached 2.49MPa and 1.43MPa, 193% and 117% higher than SPI adhesive, respectively. Molecular docking simulations were used to verify that the introduction of modifiers significantly improved the stability and crosslinking strength of the adhesive. The best ratio of the SPI-RGT-AgNP adhesive was confirmed using the response surface methodology (RSM). Simultaneously, SPI-RGT-AgNPs adhesive also showed excellent anti-mildew and anti-microbial efficiencies to Escherichia coli (98.18%) and Staphylococcus aureus (99.33%). In addition, a life-cycle assessment was used to explore the pollution emissions from the adhesives. As compared to formaldehyde-based adhesives, the SPI-RGT-AgNP adhesive had lower energy consumption and pollution emissions. Therefore, this study prepared a novel high-strength and multifunctional soy protein adhesive, guiding the production of multifunctional and green adhesives.

Assessing bonding and debonding properties of Evotherm modified bitumen with natural aggregates using surface free energy approach

ABSTRACT An incongruous pairing of aggregates and bitumen can result in early pavement failures such as stripping, raveling, and fatigue cracking. Surface free energy (SFE) assessments of aggregates and bitumen offer a means to evaluate the compatibility of the aggregate-bitumen system. It is important to emphasise that the SFE of both bitumen and aggregates significantly influences the determination of a compatible aggregate-bitumen combination. In this study, the moisture damage resistance of unmodified bitumen types (VG20, VG40) and modified bitumen types (PMB40, CRMB60) incorporating chemical-based warm mix asphalt (WMA) additives, specifically Evotherm, was investigated. The SFE approach was utilised to gain insights into their performance. In the laboratory, the static contact angle and SFE parameters of both unmodified and modified bitumen, with and without Evotherm, were determined using the Sessile drop method. Five different aggregate types were employed to calculate SFE performance parameters. Subsequently, the SFE performance parameter of forty combinations of aggregates and bitumen was calculated. As part of the assessment of moisture damage resistance, the compatibility ratio (CR) parameter was estimated using the dry adhesion energy, bitumen cohesion energy, wet adhesion energy, and wettability of different combinations of bitumen with aggregates. From the result, Evotherm addition to base bitumen (excluding VG20) significantly improved CR across various aggregates. Notable increases were observed for VG40, PMB40, and CRMB60 after Evotherm addition, with improvements of 66.67%, 48.48%, and 64.54% respectively for basalt aggregate. PMB40+EM with basalt aggregate exhibited the highest CR and Tensile Strength Ratio (TSR), suggesting superior moisture damage resistance compared to other bitumen combinations.

The strength of an adhesive contact in the presence of interfacial defects

Adhesive contacts which possess a dominant stress concentration, such as at the contact edge in spherical junctions or at the detachment front in a peeling film, are well studied. More complex adhesive junction geometries, such as mushroom-shaped fibrils in bioinspired micropatterned dry adhesives, have exhibited a complex dependence of adhesive strength on the presence of interfacial defects within the contact. This has led to the emergence of statistical variation of the local behavior among micropatterned sub-contacts. In order to examine the interplay between geometry and interfacial defect character in control of the adhesive strength, the model system of a stiff cylindrical probe on an elastic layer is examined. Both experiments (glass on PDMS) and cohesive zone finite element simulations are performed, with analytical asymptotic limits also considered. The thickness of the elastic layer is varied to alter the interfacial stress distribution, with thinner layers having a reduced edge stress concentration at the expense of increased stress at the contact center. The size and position of manufactured interfacial defects is varied. It is observed that for the thickest substrates the edge stress concentration is dominant, with detachment propagating from this region regardless of the presence of an interfacial defect within the contact. Only very large center defects, with radius greater than half of that of the contact influence the adhesive strength. This transition is in agreement with analytical asymptotic limits. As the substrate is made thinner and the stress distribution changes, a strong decay in adhesive strength with increasing center defect radius emerges. For the thinnest substrate the flaw-insensitive upper bound is approached, suggesting that this decay is dominated by a reduction in the contact area. For penny-shaped defects at increasing radial positions, the adhesive strength for the thinnest substrates becomes non-monotonic. This confirms an intricate interplay between the geometry-controlled interfacial stress distribution and the size and position of interfacial defects in adhesive contacts, which will lead to statistical variation in strength when defects form due to surface roughness, fabrication imperfections, or contaminant particles.

Adhesion of a nematic elastomer cylinder.

Reversible dry adhesion is exploited by lizards and insects in nature, and is of interest to robotics and bio-medicine. In this paper, we use numerical simulation to study how the soft elasticity of liquid crystal elastomers can affect its adhesion and provide a technological opportunity. Liquid crystal elastomers are cross-linked elastomer networks with liquid crystal mesogens incorporated into the main or side chain. Polydomain liquid crystalline (nematic) elastomers exhibit unusual mechanical properties like soft elasticity, where the material deforms at nearly constant stress, due to the reorientation of mesogens. Our study reveals that the soft elasticity of nematic elastomers dramatically affects the interfacial stress distribution at the interface of a nematic elastomer cylinder adhered to a rigid substrate. The stress near the edge of the nematic cylinder under tensile load deviates from the singular behavior predicted for linear elastic materials, and the maximum normal stress reduces dramatically. This suggests that nematic elastomers should display extremely high, but controllable adhesion, consistent with the available experimental observations.

Intelligent marine waterborne epoxy coating based on functionalized multiscale nanocomposite: mechanical enhancement, self-reporting, and active/passive anti-corrosion

Corrosion activities and related accidents are significant issues for marine facilities, leading to considerable economic losses. Waterborne epoxy (EP) coating has been seen as one of the optimal options for corrosion protection due to its stable properties and eco-friendliness (0 g/L volatile organic compounds). Nevertheless, several intrinsic deficiencies require improvement, such as fragile mechanical properties and defects (macro and micro), resulting in the continuous deterioration of comprehensive coating performances. In this work, a novel nanocomposite coating with mechanical enhancement, intelligent self-reporting, and active protection is fabricated by integrating the functionalized and compatible graphene oxide/cerium based metal-organic framework multiscale structure (GO-CeMOF-P/M). Notably, the homogenous dispersion of GO-CeMOF-P/M and its chemical interaction with the polymer matrix effectively reduces the defects resulting from solution volatilizing and enhances the compactness, which boosts the tensile strength (32.1 MPa/8.5%) and dry adhesion force (5.8 MPa) of the coating. Additionally, the controllable responsiveness and release of multiscale nanocomposite within external environments endow intelligent active protection and self-reporting characteristics for the GO-CeMOF-P/M-EP coating, making it especially suitable for a variety of practical marine applications. Furthermore, following immersion of 80 d in the aggressive environment, Zf=0.01 Hz value of GO-CeMOF-P/M-EP coating is 1.2 × 1010 Ω·cm2, which is 164.4 times larger than that of EP coating (7.3 × 107 Ω·cm2), demonstrating remarkably strengthened anti-corrosion ability. Consequently, by offering an intriguing design strategy, the current work anticipates addressing the inherent deficiencies of EP coating and facilitating its practicality and feasibility in real sea environments.

Ladybug-inspired hierarchical composite adhesives for enhanced surface adaptability

Abstract Enhanced adhesion on rough surfaces is highly desired for a wide range of applications. On the other hand, surface roughness compatibility and structure stability are two critical but competing factors for biologically-inspired dry adhesives in the real world. Inspired by ladybug, a hierarchical structural composite dry adhesive (denoted as PP-M) with enhanced robustness on surface roughness is developed, which is composed of a thin compliant contact layer (a thin soft polydimethylsiloxane (PDMS) film supported discretely by PDMS micropillars) and a rigid bottom layer magnetorheological elastomers (MREs). The PP-M shows a high pull-off strength of 8.2 N cm−2 on a smooth surface and nano-scale rough surface at a mild preload (2 N cm−2). For micro-scale rough surfaces, the PP-M exhibits better surface adaptability compared to the double-layered adhesive (PDMS on MRE) without micropillar support. The increased compliance of the contact layer also leads to a 2.11 fold superior pull-off strength at a wider range of roughness (Sq > 2.23 μm). Element analysis confirms PP-M’s enhanced adaptability, attributed to deeper indentation and lower contact stress. This hierarchical composite structure in PP-M, characterized by a ‘soft on top and hard on bottom’ stiffness distribution, synergizes the flexible contact layer with the stiff MRE bottom layer, leading to superior adhesive properties. The results provide a new reference for achieving enhanced adhesion on rough surfaces.

Bioinspired Nanocomposite Dry Adhesives Applicable Over a Wide Temperature Range

AbstractBioinspired structural adhesives have shown great potential in the field of industrial manipulation and locomotion. However, such adhesives usually perform great adhesion performance at room temperature, reliable adhesion under high‐temperature conditions remains a major challenge and is rarely investigated, which severely limits the applications of current bioinspired adhesives. Here, a bioinspired adhesive structure based on fluororubber (FKM) and nanofillers is proposed. The adhesive structure has a “suction cup‐shaped” tip that mimics the special structural configuration of the adhesive setae of Dytiscus lapponicus, and the ability to regulate the structural modulus by adjusting the content of nanofillers, as well as exhibiting strong and contamination‐free adhesion (>350 kPa) with high adhesive efficiency (up to 77.7) in a wide temperature range (from room temperature to high temperatures (>200 °C)). Moreover, the adhesion performance can be enhanced by precisely regulating the structural modulus, and the enhancement mechanism is demonstrated based on the cohesive zone theory. The proposed adhesion strategy expands the application areas of dry adhesives from room‐ to high‐temperature conditions, especially for the pick‐up and transfer of thin and fragile materials that require high‐temperature operation, opening an avenue for the development of devices and systems based on dry adhesives.

The adjustable adhesion strength of multiferroic composite materials via electromagnetic loadings and shape effect of punch

Tunable and reversible dry adhesion possess great potential in a wide range of applications including transfer printing, climbing robots, wearable devices/electronics, and gripping in pick-and-place operations. Multiferroic composite materials offer new routines and approaches to achieve tunable adhesion due to their multi-field coupling effects. In this paper, the classical Johnson-Kendall-Roberts (JKR) adhesion model is extended to investigate the adhesive contact problem of a multiferroic composite half-space indented by an axisymmetric power-law shaped punch, whose shape index is denoted by n. The JKR-n adhesion models under the action of the power-law shaped punches with four different electromagnetic properties are set up by means of the total energy method. The explicit analytical expressions relating the indentation load and indentation depth to the contact radius are obtained, which can include the existing results in open literature as special cases. The generalized Tabor parameter and the interfacial adhesion strength applicable to multiferroic composite materials are defined. The effects of the shape index and the electromagnetic loadings on adhesion behaviors are revealed. It is found that both of them have prominent influences on the relationships among the indentation load, indentation depth and contact radius, the contact radius and indentation depth at self-equilibrium state, and the critical contact radius and indentation depth at pull-off moment. The pull-off force under the action of the conducting spherical punch subjected to non-zero electromagnetic loadings is dependent on material properties, which is different from the classical JKR result. More importantly, our analysis indicates that the pull-off force and the interfacial adhesion strength can be adjusted via altering the electromagnetic loadings and the shape index of the punch, which provides new approaches to achieve tunable adhesion.

Effects of liquid lubricants on the surface characteristics of 3D-printed polylactic acid

In this study, 3D-printed Polylactic acid (PLA) specimens were manufactured and polished using various lubricants to assess their surface, friction, and wear characteristics. After polishing, the surface roughness decreased by approximately 80% compared with that before polishing, except when acetone was used as the lubricant. In particular, under deionized (DI) water and acetone lubrication conditions, the friction coefficient decreased by 63% and 70%, respectively, whereas the specific wear rate decreased by 88% and 83%, respectively, compared with the unpolished specimens. In the case of dry polishing, adhesion, friction, and wear increase owing to surface damage. Ethanol and IPA polishing resulted in hydrolysis and increased friction, but slightly decreased wear rates. The surface of the specimen polished with acetone dissolved and became very rough. Only the surface polished with DI water exhibited hydrophobic properties. When acetone and DI water were used as lubricants, the surface adhesion force, adhesion energy, friction coefficient, and wear rate were lowest. The finite element analysis results showed that the polished surface exhibited stable contact pressure and friction force, while the unpolished surface showed large fluctuations in contact pressure and friction force owing to the laminated pattern. These results suggest that the polishing process is crucial for improving the surface characteristics and mechanical performance of 3D-printed PLA parts.

Effect of side group modification on the glass transition and adhesion properties of polysiloxane at the atomic scale

Polysiloxane is a typical biomimetic dry adhesive, and polysiloxane-silica interface is a typical interface widely existing in test systems and wall-climbing robots. Studying the glass transition temperature (Tg) of polysiloxane and its adhesion properties on silica surfaces has important theoretical guiding significance and practical value for developing and applying a new generation of dry adhesion functional surfaces and devices. However, the effect of the type and content of side groups on the Tg and adhesion properties of polysiloxane is still unclear. Therefore, three side group combinations are included in the established modified polysiloxane models, with each type corresponding to five different side group contents. Molecular dynamics (MD) is used to investigate the effect of side group modification on the Tg of polysiloxane and the adhesion properties on the silica surface. The results show that, compared with polydimethylsiloxane (PDMS), introducing phenylmethyl or diphenyl into the polysiloxane increases the Tg in the studied range of side group contents. The introduction of diethyl decreases the Tg. The corresponding interfacial interactions are enhanced when the diethyl content is 2 %, 4 % and 10 %, the phenylmethyl content is 4–10 % and the diphenyl content is 2–10 %. The interfacial interactions are weakened at the unmentioned side group content. The ratio of van der Waals energy to the interfacial interaction energy is above 94.5 % in all interfaces, which means that van der Waals interaction dominates the interaction between polysiloxane and silica surface. The present model provides a deeper insight into polysiloxane, which may contribute to designing future bioinspired dry adhesives.

A novel methodology for intrinsic adhesion state sensing in gecko-inspired directional dry adhesives

This paper introduces an innovative methodology designed for intrinsic sensing of the adhesion state in directional dry adhesives. Rooted in the inherent shear actuation requirements of these adhesives, the sensing framework incorporates an elastic beam model for a single seta and an equivalent spring model for setae arrays during actuation, facilitating the transformation of complex micro-scale contact issues into relatively simple mechanical measurements. Using microwedge adhesives as a representative case study, the methodology is validated by a series of quantitative experiments and an experimental robotic gripper scenario, in which a straightforward and cost-effective commercial strain gauge proves competent for complex contact state sensing. The proposed methodology indicates substantial implications for improving the operational performance and expanding the application range of gecko-inspired adhesive operations.

Democratising dry adhesion development with consumer-grade AM

AbstractThe production of reusable gecko-inspired dry adhesives has traditionally been done with complex nanofabrication methods such as lithography and PDMS casting. This article presents a way of producing and testing dry adhesive samples using consumer-grade AM machines and equipment typically available in a Makerspace. The samples produced exhibit adhesive properties depending on the preload and surface structure, and we conclude that consumer-grade AM is suitable for rapid prototyping and testing of dry adhesion. However, it is limited by the scale and accuracy compared to traditional methods.

Constructing reactive “rod-bead” nanohybrid-driven high-efficient crosslinking network for the preparation of strong and tough plant protein adhesive

There still exist challenges to regulate the crosslinking network of soybean flour (SF) precisely with both strong and tough mechanical properties to match adhesion requirements of wood adhesives applications. Herein, a novel nanohybrid crosslinker with dynamic bonding effect was synthesized and then employed to improve SF adhesives. Dimethylglyoxime as chain extender was incorporated into polyurethane cooperating with CuO to form dynamic coordination bonds, after which epoxy and siloxane dual-functionalized polyurethane was co-deposited onto cellulose nanocrystal (CNC) surface to construct reactive “rod-bead” nanohybrid named CuOGU@CNC. It is found that epoxy groups induce CuOGU@CNC to form covalent crosslinking interactions with SF matrix constructing a stable adhesive system. Meanwhile, the dynamic coordination bonds of dimethylglyoxime and CuO serve as sacrificial units to contribute for energy dissipation, during which the unique “rod-bead” structure increases contact efficiency between DMG and CuO to optimize bonding exchange rate to high-effectively redistribute stress during loading. Given on the effect, the adhesives modified by CuOGU@CNC present improved dry and wet adhesion strength, and adhesion toughness compared to pristine SF sample. This work can provide a facile strategy to prepare high-performance wood adhesives aiming to meet higher applicational standard.

Wheel-legged In-pipe Robot with a Bioinspired Hook and Dry Adhesive Attachment Device

Wheel-legged In-pipe Robot with a Bioinspired Hook and Dry Adhesive Attachment Device

Development of a Stretchable and Removable Electrical Interconnection Solution for Ultra-Thin Electronic Components

Currently, the solutions for interconnecting electronic components with their active face facing on substrates are based on metallic soldering. The mechanical contacts are therefore rigid. In order to enhance the reliability of the bonding, underfill is usually used to redistribute the thermo-mechanical stress created by the Coefficient of Thermal Expansion (CTE) mismatch between the silicon chip and substrate. Underfill is done with epoxy resins containing silica fillers (SiO2). As a result, the removal of components is no longer possible. Moreover, this solution is not suitable for devices integrating ultra-thin silicon components (<100 μm) hybridized on flexible substrates that may be subject to deformation. This is the case, for example, of medical “patches” worn on the person and continuously solicited. Indeed, the rigid contact points are likely to break. To address this issue, we are developing a thin anisotropic conductive and stretchable adhesive film inspired by the adhesion of the gecko. Thanks to the microstructuration of its toes involving about 1 million setae, the gecko can develop a large contact surface and thus a large force of attraction by the multiplication of van der Waals interactions. In this work, this “dry adhesion” based on the principle of “contact splitting”, was implemented in order to improve the adhesion of a flexible interconnection. For this purpose, the surface of a polydimethylsiloxane (PDMS) film was structured with micrometric mushroom-shaped patterns known to be the most efficient form of contact. To this end, silicon molds with varying mushroom geometries were used to shape the PDMS (with different cap and pillar diameters) and the adhesion force microstructured films were assessed (shear and pull-off experiments). To make these films locally conductive through the thickness, a conductive composite was prepared and locally deposited in the mold. One approach we investigated, was using a screen-printing mask. This approach has been implemented and characterized using electrical tests (I-V measurements) in order to select the most suitable films to make a flexible interconnection.

Pneumatically tunable adherence of elastomeric soft hollow pillars with non-circular contacts

Dynamically tunable interfacial dry adhesion plays a significant role in numerous biological functions and industrial applications. Among various strategies, pneumatics-activated adhesive devices draw much attention due to their distinct advantages such as fast speed, reliable performance, large adhesion tunability and easily accessible materials. To understand and predict adhesion strength of pneumatics-activated adhesives, it is necessary to examine their interfacial mechanics that is nonlinearly coupled with the large deformation of the devices under pressure. However, previous studies have only focused on axisymmetric cases in which the outline of the contact area is circular, whereas the tunable adherence of non-circular contact controlled by pneumatics remains elusive. In this work, through a combination of experiments and simulations, we study the effect of non-circular contact geometry on tunable dry adhesion of pressure-activated soft hollow pillars. Specifically, elliptical, square, and rectangular contact shapes are considered and their effects on tunable adhesion of the soft hollow pillars are compared to that of circular contact geometry thoroughly. The results show that soft hollow pillars with elliptical, square, and rectangular contact surfaces demonstrate rich interfacial delamination behaviors that depend on the contact outline geometry and internal pressure. Among all contact geometries, elliptical contact has the highest adhesion tunability yet requires lowest activating pressure owing to the non-uniform curvature distribution of the contact outline. However, when the eccentricity increases, the elliptical contact has reduced tunability of adhesion caused by the contact of opposing sides of the sidewall upon buckling. For square and rectangular contacts, they have the lowest adhesion tunability and need higher activating pressure than those of circular and elliptical contact since the 90-degree edges of the sidewall prohibit buckling instability. Our findings greatly broaden the design space of pneumatics-activated adhesive devices by adding the contact geometry of the soft hollow pillars as a new design parameter, which can provide valuable guidance for tunable adhesive design for various applications in manufacturing and robotics.

Theoretical optimization of micropillar arrays for structurally stable bioinspired dry adhesives

Inspired by the excellent adhesion performances of setae structure from organisms, micro/nano-pillar array has become one of the paradigms for adhesive surfaces. The micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for supporting. The stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays, yet the design for the stability of the micropillar array lacks systematical and quantitative guides. In this work, we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical calculations. The predictions for the stress within the singularity field can be obtained based on the full expressions of the stress. The good agreement between the predictions and the FEM results demonstrates the high reliability of our method. By adopting the strain energy density factor approach, the stability of the pillar-substrate corner is assessed by predicting the failure at the corner. For the elastic mismatch between the pillar and substrate given in this paper, the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the micropillar. Our study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.

Polydimethylsiloxane based dry adhesives produced using a replica molding technique.

Dry adhesives have gained considerable interest due to their applications in a wide variety of areas. This study used a replica molding technique to produce micron-sized pillars on the surface of polydimethylsiloxane (PDMS) and investigated their dry adhesion behaviour. Shear adhesion for the produced samples is measured using a tensile testing machine. For this purpose, the sample was initially brought into contact with a glass slide. Following this, the shear adhesion was determined by measuring the shear stress required to slide the sample along the glass slide. Peel adhesion of the samples was measured using an in-house designed and built peel fixture. The force required to peel the sample from the surface of the fixture was measured to determine the peel strength. The shear adhesion and peel tests were also conducted on neat PDMS to determine the effect of surface micropillars on the adhesion performance of the samples. The results show that the shear adhesion strength was 0.12 N cm-2, while the shear adhesion strength of neat PDMS was determined to be 0.02 N cm-2. Similarly, the peel strength of the samples was recorded to be 0.15 N cm-2 compared to 0.05 N cm-2 recorded for neat PDMS.

A supramolecular approach for converting renewable biomass into functional materials.

The rational transformation and utilization of biomass have attracted increasing attention because of its high importance in sustainable development and green economy. In this study, we used a supramolecular approach to convert biomass into functional materials. Six biomass raw materials with distinct chemical structures and physical properties were copolymerized with thioctic acid (TA) to afford poly[TA-biomass]s. The solvent-free copolymerization leads to the convenient and quantitative fabrication of biomass-based versatile materials. The non-covalent bonding and reversible solid-liquid transitions in poly[TA-biomass]s endow them with diversified features, including thermal processability, 3D printing, wet and dry adhesion, recyclability, impact resistance, and antimicrobial activity. Benefiting from their good biocompatibility and nontoxicity, these biomass-based materials are promising candidates for biological applications.

Adhesion theory and model for air humidity impact on dust emission

It has been suggested that air humidity influences dust emission under very dry conditions and adhesion might be the responsible process which changes the binding between soil particles. The process of adhesion is so far poorly understood and difficult to quantify. Here, a critical examination of the relevant studies is provided, and an adhesion model is proposed. Both isothermal-kinematic and diffusion processes can limit the soil liquid–water and water–vapor exchange in soil, but for the particle size range concerned in aeolian studies, diffusion appears to be the limiting process. The model shows that soil moisture in the topsoil layers is positively correlated with air humidity, but with delays of several hours. The model performance is influenced by several parameters but is particularly sensitive to the equilibrium soil water–vapor content. This implies that soil microscopic properties can strongly influence adhesion. A new formulation of soil water retention function covering the entire soil moisture range is also proposed, which links soil water retention function and pore size distribution. Using a relationship between soil particle-size and pore-size distributions, an adhesion-affected grain size can be estimated, which defines the upper size limit of soil particles influenced by soil moisture. This study explains how air humidity influences soil moisture through adhesion and dust emission and why low air humidity promotes the emission of finer dust particles.