Solid-like Layer Research Articles

Wettability-dependent thermal transport at the Fe nanoparticle-water interface: Molecular dynamics simulations

Nanoparticles are pivotal in applications such as solar thermal utilization, drug delivery, and water treatment. However, the microscopic mechanisms of heat transfer between nanoparticles and water, especially considering wettability effects, remain poorly understood. This study aims to investigate the interfacial heat transport properties of Fe nanoparticles-water using molecular dynamics simulations with varying levels of wettability. And the results indicate that the thermal conductance at the interface between Fe nanoparticles and water is 97.9 × 108 W/m2 K. The study also reveals an oscillatory pattern in the water density near the Fe nanoparticle interface, resulting in a distinct “double-density peak” With increased wettability, this peak density consistently grows, while the thickness of the adjacent solid-like layer remains relatively unchanged. Through the analysis of the vibrational density of states at the interface, the study reveals the microscopic mechanism by which wettability affects the thermal conductance of the Fe nanoparticles-water interface. Enhanced wettability improves the coupling of low-frequency phonon modes across the solid-liquid boundary, increasing thermal energy transfer efficiency. The study further identifies that low-frequency transverse modes play a vital role in heat transfer at the interface. Consequently, these insights provide a valuable theoretical framework for comprehending heat transport mechanisms at soft-hard interfaces.

Friction forces determine cytoplasmic reorganization and shape changes of ascidian oocytes upon fertilization

Contraction and flow of the actin cell cortex have emerged as a common principle by which cells reorganize their cytoplasm and take shape. However, how these cortical flows interact with adjacent cytoplasmic components, changing their form and localization, and how this affects cytoplasmic organization and cell shape remains unclear. Here we show that in ascidian oocytes, the cooperative activities of cortical actomyosin flows and deformation of the adjacent mitochondria-rich myoplasm drive oocyte cytoplasmic reorganization and shape changes following fertilization. We show that vegetal-directed cortical actomyosin flows, established upon oocyte fertilization, lead to both the accumulation of cortical actin at the vegetal pole of the zygote and compression and local buckling of the adjacent elastic solid-like myoplasm layer due to friction forces generated at their interface. Once cortical flows have ceased, the multiple myoplasm buckles resolve into one larger buckle, which again drives the formation of the contraction pole—a protuberance of the zygote’s vegetal pole where maternal mRNAs accumulate. Thus, our findings reveal a mechanism where cortical actomyosin network flows determine cytoplasmic reorganization and cell shape by deforming adjacent cytoplasmic components through friction forces.

Molecular Dynamics Simulation Study on the Occurrence of Shale Oil in Hybrid Nanopores.

The molecular dynamics simulation was used to simulate the influence of the composite wall stacking effect on shale oil occurrence. The kerogen-illite heterogeneous wall pore model was established to study the effects of temperature, pore size, and wall component ratio on the adsorption ratio and diffusion capacity of shale oil. The calculation results show that the fluid density distribution in the hybrid nanopore is not uniform. When the pore size increases, the proportion of the first adsorption layer to the total adsorption amount decreases rapidly, and the phenomenon of the "solid-like layer" of shale oil in small pores is more obvious. In addition, increases in temperature have little effect on the density peak of the first adsorption layer. With increases in organic matter content in the shale pore model, the diffusion coefficient of fluid decreases gradually, along with adsorption capacity. The influence of the irregular arrangement of kerogen molecules on the adsorption of shale oil is greater than the influence of surface roughness caused by illite on the adsorption.

Incorporating soy protein hydrolysate and temperature-induced gelling polysaccharide as partial egg replacements for enhanced texture in sponge cake

This study investigated the influence of hydroxypropyl methylcelluloses (HPMCs), temperature-induced gelling polysaccharides, on the air-water interfacial properties and foaming properties of four soy proteins. Two HPMCs with different relative molecular masses (F50, lower; K4M, higher) were combined with soy protein isolate (SPI), 7S fraction (7S), selective hydrolysate by pepsin (SPSH), and limited hydrolysate by papain (SPLH). Interfacial shear rheology results showed that SPSH exhibited the highest G′ value, indicating a multi-layer adsorption structure formed due to both 7S and low molecule peptides in SPSH. Adding F50 to SPI, 7S, and SPSH improved foam expansion and stability while adding K4M negatively impacted the foam expansion of SPI, 7S, and SPSH but enhanced the foam expansion of SPLH. These findings suggest that the interfacial interaction patterns between HPMCs and soy proteins are significantly influenced by the molecular weight of HPMCs and the structure of the protein. Incorporating F50 into SPSH decreased the gelation temperature, shortened the formation time of a solid-like layer at the air-water interface, and expanded the linear viscoelastic region during structural fraction testing. Consequently, the combination of F50 and SPSH was chosen as the viable alternative to egg protein in sponge cake, as it facilitated rapid foam stability and prevented collapse during baking. The resulting sponge cake, with half of the egg replaced by the SPSH/F50 mix, exhibited a similar appearance and texture to that with only the egg added. Thus, combining temperature-induced gelling polysaccharides with SPSH offers a promising alternative to egg protein in aerated bakery food production.

Regulation of interfacial mechanics of soy protein via co-extraction with flaxseed protein for efficient fabrication of foams and emulsions

Enrichment of plant proteins with functionality is of great importance for expanding their application in food formulations. This study proposed an innovation to co-enrich soy protein and flaxseed protein to act as efficient interfacial stabilizers for generating foams and emulsions. The structure, interfacial properties, and functionalities of the soy protein-flaxseed protein natural nanoparticles (SFNPs) obtained by alkali extraction-isoelectric precipitation (AE) and salt extraction-dialysis (SE) methods were investigated. Overall, the foamability of AE-SFNPs (194.67 %) was 1.45-fold that of SE-SFNPs, due to their more flexible structure, smaller particle size, and suitable surface wettability, promoting diffusion and adsorption at the air–water interface. AE-SFNPs showed higher emulsion stability (140.89 min), probably because the adsorbed AE-SFNPs with smaller size displayed soft particle-like properties and stronger interfacial flexibility, and therefore could densely and evenly arrange at the interface, facilitating the formation of a stiff and solid-like interfacial layer, beneficial for more stable emulsion formation. The findings may innovatively expand the applications of SFNPs as food ingredients.

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Nanofluids based on extended nanostructures, such as nanowires, have been demonstrated improved thermal conductivities (κ). However, the lack of a complete understanding at the microscopic level hinders the development of such nanofluids towards practical applications. We aim to provide it by investigating how the interface thermal resistance (R b ), ballistic phonon transport, and the solid-like liquid layer affect the heat conduction in nanowire-based nanofluids. By employing Non-Equilibrium Molecular Dynamics (NEMD), it is found that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the R b . This contradicts the predictions of the classical parallel heat conduction model, therefore, a novel model is proposed taking this coupled behavior into account. Using this model, it is shown that the high κ of the solid phase has a limited contribution to the effective κ of nanofluids having short nanowires due to the dominant R b effect. For the case of long nanowires, however, the individual nanowire κ becomes a vital parameter defining the effective κ. Further, NEMD calculations reveal that the κ of suspended nanowires in a liquid is markedly reduced, questioning the validity of classical effective medium theories which use the bulk parameters. This reduction is attributed to surface atoms’ restricted vibrational freedom and the nanowire’s phonon-boundary scattering. By substituting this reduced κ of the solid phase into the new mathematical model, the theoretical predictions align closely with the NEMD calculations, exhibiting deviations below 10%. The sole contribution from the solid-like liquid layer to the κ enhancement lies between 20%–30% in the nanofluids presently considered. Therefore, the findings of this study highlight the important roles play by the identified microscopic thermal characteristics in defining the effective κ of nanofluids based on nanowires.

Confined ionic liquids films under shear: The importance of the chemical nature of the solid surface.

Ionic liquids have generated interest in applications as lubricants and as additives to conventional lubricants due to their unique physical properties. In these applications, the liquid thin film can be subjected simultaneously to extremely high shear and loads in addition to nanoconfinement effects. Here, we use molecular dynamics simulations with a coarse-grained model to study a nanometric film of an ionic liquid confined between two planar solid surfaces both at equilibrium and at several shear rates. The strength of the interaction between the solid surface and the ions was changed by simulating three different surfaces with enhanced interactions with different ions. The increase in the interaction with either the cation or the anion leads to the formation of a solid-like layer that moves alongside the substrates; however, this layer can exhibit different structures and stability. An increase in the interaction with the high symmetry anion produces a more regular structure that is more resistant to the effects of shear and viscous heating. Two definitions were proposed and used for the calculation of the viscosity: a local definition based on the microscopic characteristics of the liquid and an engineering definition based on the forces measured at the solid surfaces, with the former displaying a correlation with the layered structure induced by the surfaces. Because of the shear thinning behavior of the ionic liquids as well as the temperature rise brought on by viscous heating, both the engineering and the local viscosities decrease as the shear rate increases.

Investigating convective heat transfer coefficient of nanofluid Couette flow in a nanochannel by molecular dynamics simulation

ABSTRACT The present study investigates convective heat transfer of nanofluid Couette flow. For this purpose, Ar-Cu nanofluid (argon as base fluid with spherical copper nanoparticles) is simulated using the LAMMPS package. The convective heat transfer coefficient is calculated for nanofluid and base fluid. The results show that the heat transfer coefficient increases with the addition of nanoparticles. This is due to changes in the structure and behaviour of the nanofluid relative to the base fluid. One of the important effects of the presence of nanoparticles is the constitution of solid-like layer adjacent to the nanoparticles, which increases the capability of heat transfer. Also, the velocity and mobility of base fluid are affected by the presence of nanoparticles, and velocity profile deviates from the linear mode. The effects of volume fraction and diameter of nanoparticles on convective heat transfer are also investigated. For a constant diameter of nanoparticles, the convective heat transfer coefficient of nanofluid increases by increasing the volume fraction. Likewise, in a constant volume fraction, the convective heat transfer coefficient decreases with increasing the nanoparticles diameter. This is because of the reduction in adsorption of fluid atoms by copper nanoparticles and decreasing the solid-like layer thickness.

Short to medium range order and atomic dynamic property within the surface of nanoscale metallic glasses revealed by molecular dynamics simulations

The surface microstructure and its atomic dynamic property of a metallic glass nano pillar were investigated by using molecular dynamics simulations. The short-range order motifs in the surface contain a large number of unstable bonded pairs and clusters, leading surface to approach the structural property of liquid phase. A proportion of <0, 0, 12, 0> clusters in the surface constitute chain-like super clusters, but its overall degree of medium-range order is lower than that in the core region. The atomic mobility in the surface at different scales are enhanced significantly. Generally, the lower the degree of order for the cluster, the stronger its migration ability. The surface region could be divided into three consecutive sublayers, which are solid-like layer, semi-solid layer and liquid-like layer. The content of liquid-like clusters increases sequentially in these three sublayers. A schematic illustration of the relationship between the hierarchical structure and the possible relaxation modes was proposed.

Influence of non-thermal microwave radiation on emulsifying properties of sunflower protein

Sunflower protein isolate obtained from industrially de-oiled press cake was treated with non-thermal microwave, aiming to investigate how structure and emulsifying properties were affected. Our results indicated that the content of polar amino acids was decreased and solubility and surface hydrophobicity were altered upon exposure to non-thermal microwave. Higher solubility and surface hydrophobicity of the samples treated with defrost mode and also 350 W were accompanied by a smaller size and lower uniformity of the oil droplets compared to the control and other samples. Non-thermal microwave treatment improved the emulsion stability by 1.43 times and defrost mode treated sample had the lowest stability index after 120 min. Interfacial dilatational rheology measurements revealed that 70 and 350 W treated samples created higher elastic, less stretchable solid-like layer at the O/W interface in comparison with defrost mode treated and control samples. Consequently, non-thermal microwave treatment could be considered as a promising simple, fast, and “green” protein modification technique.

Competition of rapeseed proteins and oleosomes for the air-water interface and its effect on the foaming properties of protein-oleosome mixtures

There is an increasing interest to apply oleosomes (plant oil storage organelles) as natural oil droplets in food systems. Lipids are usually known to be detrimental for protein-stabilised foams due to the weakening of interactions between adsorbed proteins, or by forming oil bridges between two protein surfaces. Both mechanisms can lead to film rupture, and thereby destabilise protein-stabilised foams. Little is known about the influence of oleosomes on protein-stabilised interfaces and foams. Therefore, these properties were studied for rapeseed protein–oleosome mixtures at various protein concentrations and ratios. At 0.1 and 0.2% (w/w) protein content, oleosomes were found to co-adsorb with proteins at the interface, followed by rupture of oleosomes and release of triacylglycerols and phospholipids. This led to weaker in-plane interactions between adsorbed proteins. As a result, the foamability and foam stability of protein-oleosome systems were substantially lower compared to systems made with pure proteins. At 0.5 and 1.0% (w/w) protein content, the rapeseed proteins were found to dominate the interfacial properties. The proteins formed a dense solid-like layer at such high concentrations, which prevented the oleosomes from co-adsorbing at the interface. Also, in foam systems at high protein concentrations, the proteins seemed to outcompete the oleosomes for the interface, leading to higher foam stability. Here, we have demonstrated that the detrimental influence of oleosomes on protein-stabilised interfaces and foams can be controlled by varying the amount of oleosomes and rapeseed proteins in the mixture, which is a promising outcome to further utilise oleosomes in aerated food systems.

Thermal energy storage characteristics of binary molten salt nanofluids: Specific heat and latent heat

This study aims to examine the thermal energy storage characteristics, in terms of specific heat and latent heat, of nanoparticle-doped binary molten salt nanofluids. Two different binary molten salt mixtures, namely carbonate salts (Li2CO3 and K2CO3) and nitrate salts (NaNO3 and KNO3), were used as base solvents. Graphite nanoparticles were dispersed into the salt mixtures. The chemical compositions (molar fractions) of the two salt components were varied from hypoeutectic to hypereutectic, including eutectic compositions, to investigate their effects on the specific heat and latent heat of both the pure salts and their nanofluids. The specific heat of the carbonate salt nanofluid was enhanced, irrespective of the chemical composition, and the enhancement was proportional to the nanoparticle concentration. However, the specific heat of the nitrate salt nanofluid was decreased by the addition of 0.1 wt% of graphite nanoparticles and increased by the addition of a larger amount of 1 wt%. The latent heat of the nanofluids was enhanced by doping nanoparticles into the salt mixtures and was affected by the chemical composition of the solvent salt mixtures. The distinct behaviors of specific heat and latent heat obtained in this study were discussed based on a compressed liquid (solid-like) layer formed near the nanoparticles. The thermal energy storage capacities of the nanofluids were estimated and compared by using their specific heat and latent heat.

Molecular dynamics simulation of nanofluid convective heat transfer in a nanochannel: Effect of nanoparticles shape, aggregation and wall roughness

In this study, convective heat transfer of an argon-copper nanofluid in a copper nanochannel under Poiseuille flow conditions is investigated. Molecular dynamics simulation is used to study the effect of nanoparticles shape and their aggregation and also the effect of wall roughness on nanofluid Nusselt number. The number of nanoparticles is considered to be 4 and the volume fraction of the nanoparticles in the simulations is 1.4%. In order to investigate the effect of nanoparticles shape, the nanoparticles with cylindrical and spherical shapes are investigated. The results show that the convective heat transfer is affected by the shape of the nanoparticles. This is due to a difference in the velocity and structure of the nanofluid atoms. The results also show that the aggregation of nanoparticles reduces the mobility of the atoms and the amount of solid-like layer around the nanoparticles, which reduces the Nusselt number. In addition, the study of the roughness effect shows that it improves the heat transfer between the nanofluid and the wall. This is due to an increase in the thickness of the solid-like layer adjacent to the wall, as well as an increase in the mobility of the nanofluid atoms.

Simulating the convective heat transfer of nanofluid Poiseuille flow in a nanochannel by molecular dynamics method

Abstract This paper investigates convective heat transfer of nanofluid flowing through a copper nanochannel. Ar − Cu Nanofluid is used to study in the nanochannel. Simulations are performed by LAMMPS code and the effects of nanoparticles presence on convective heat transfer are investigated. For this purpose, Nusselt number for nanofluid is calculated and compared with base liquid. The results indicate that the presence of nanoparticles increases the Nusselt number, which is due to the change in the velocity and structure of base liquid atoms. Furthermore, the investigation of Nusselt number for nanofluid shows that it is affected by diameter and volume concentration of nanoparticles. In a same volume concentration, with the increase in diameter, the ratio of the surface to the volume of nanoparticles decreases. This reduces the fluid atoms mobility caused by the presence of nanoparticles. Also, decreasing this ratio reduces the amount of solid-like layer in vicinity of the nanoparticles, which decreases the heat transfer capability in the nanochannel. However, for constant diameter, the Nusselt number increases with increasing volume concentration, which is due to the increase in the number of nanoparticles and existence of more space for fluid atoms absorption.

Effect of alkane chain length on tribological properties of straight chain alkane liquid film

How to overcome the friction between the micro components has become a key point of the successful operation of the micro/nano-electric mechanical systems. The understanding of the friction mechanism of the alkane liquid film confined between two substrates is important when the friction law on a macro/nano scale is not applicable. In this work, the molecular dynamics simulations are used to study the effect of the chain length on the friction properties of the liquid films that are confined between two golden substrates. There are seven pure alkane liquid films that are composed of one molecule C&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;H&lt;sub&gt;2&lt;i&gt;n&lt;/i&gt; + 2&lt;/sub&gt;(&lt;i&gt;n&lt;/i&gt; = 6, 8, 10, 12, 14, 16, 18), and six mixed alkane liquid films that are composed of two molecules C&lt;sub&gt;6&lt;/sub&gt;H&lt;sub&gt;14&lt;/sub&gt;/C&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt;H&lt;sub&gt;2&lt;i&gt;n&lt;/i&gt; + 2&lt;/sub&gt;(&lt;i&gt;n&lt;/i&gt; = 8, 10, 12, 14, 16, 18) with a ratio of 1∶1. The results show that the friction force and the coefficient of friction of pure alkane liquid films both increase as the chain length increases when the carbon atom number is less than 12, whereas the friction property keeps stable when the carbon atom number of the alkane molecule is greater than 10 and the pure hexadecane liquid film has the largest friction force. In the mixed films, the addition of short chain alkane molecules can strengthen the friction, and the hexane/dodecane mixed film has the maximum friction force. The short chain molecule dilutes the C&lt;sub&gt;8&lt;/sub&gt;H&lt;sub&gt;18&lt;/sub&gt; film and C&lt;sub&gt;10&lt;/sub&gt;H&lt;sub&gt;22&lt;/sub&gt; film which cause the friction force to decrease. During the sliding progress, the formation of solid-like high density-packet layers is the main reason for the friction reduction. When no solid-like layer or just one solid-like layer is formed at the interface of golden base, the liquid alkane film is liquid-like and its viscosity becomes much larger than that in the normal state, which leads to high friction force. The short chain molecules reduce the density of the solid-like layers, which causes the film to transform from solid-like state to liquid state, thus resulting in the increase of friction. The friction property mainly depends on the layered structure, and the interaction between the golden surface and liquid film contributes to the friction. This study helps to understand the friction mechanism of ultra-thin liquid films.

A combined molecular dynamics simulation and quantum mechanics study on the physisorption of biodegradable CBNAILs on h-BN nanosheets.

The nanoscopic structure of biodegradable choline-based naphthenic acid ionic liquids near the hexagonal boron-nitride (h-BN) surface was analyzed using quantum mechanics calculations and molecular dynamics simulations. The effects of the type of the ring (aliphatic or aromatic) and the size of the ring in the anion counterpart of the aliphatic ionic liquids (ILs) on the configurations, binding energies, orbital energies, density of states, charge transfer, and thermochemistry of adsorption of ILs on the h-BN surface were investigated. Also the significance of non-covalent interactions on the adsorption of ILs was disclosed from the quantum theory of atoms in molecule. The results of radial distribution functions, number density, and also charge density profiles showed the existence of a solid-like bottom layer in the vicinity of the surface. Angular distribution functions revealed that while the most probable orientation in aromatic anions is parallel to the h-BN sheet, the most probable orientation in aliphatic rings apparently is perpendicular to the surface. The mobility of cations and anions in the studied ILs with respect to the h-BN sheet was analyzed using their mean square displacements. For all ions near the surface, dynamics in the parallel direction were faster than those in the z-direction due to the structuring of the solid-like layer of ILs near the h-BN surface. Altogether, this study provides new insights into the physisorption of this new class of biodegradable ILs on h-BN nanosheets at the molecular level.

Influence of exchange scattering on superfluidHe3states in nematic aerogel

The superfluid state in bulk liquid $^3$He is realized in the form of A or B phases. Uniaxially anisotropic aerogel (nafen) stabilizes transition from the normal to the polar superfluid state which on further cooling transitions to the axipolar orbital glass state (Phys. Rev. Lett. {\bf 115}, 165304 (2015)). This is the case in nafen aerogel preplated by several atomic layers of $^4$He. When pure liquid $^3$He fills the same nafen aerogel a solid-like layer of $^3$He atoms coats the aerogel structure. The polar state is not formed anymore and a phase transition occurs directly to the axipolar phase (Phys. Rev. Lett. {\bf 120}, 075301 (2018). The substitution of $^4$He by $^3$He atoms at the aerogel surface changes the potential and adds the exchange scattering of quasiparticles on the aerogel strands. A calculation shows that both of these effects can decrease the degree of anisotropy of scattering and suppress the polar phase formation. The derived anisotropy of the spin diffusion coefficient in globally anisotropic aerogel is determined by the same parameter which controls the polar state emergence which allows one to check the effect of anisotropy change for different types of covering.

Molecular dynamics simulation of the interface between sulfur mustard and graphene

Using molecular dynamics simulations, the interface between sulfur mustard (SM) which is one of the most toxic chemical warfare agents, and single layer graphene (G) was investigated for the first time to find a new class of adsorbents. Various analyses have been done in order to atomistically understand the adsorption mechanism. Results show that: (1) A solid-like SM layer of 6 Å thick is formed near G, and its density approximates to 2.5 times as large as that of the bulk SM; (2) Adsorption is occurred in three layers, and due to two distinct orientations of SM relative to G surface, i.e. parallel and tilted, there are fine structures within first layer; (3) Study of surface self-diffusion shows that the diffusion coefficient of SM molecules on G surface is half of the diffusion coefficient of SM molecules in the bulk. Furthermore, the diffusion coefficient of SM molecules with parallel orientation is half of the diffusion coefficient of tilted SM molecules and the lifetime of parallel orientation in the first adsorption layer is about three times more than that of tilted; (4) Pair interaction energy calculation between SM and G revealed that the adsorption energy of parallel SM molecules (−11.875 kCal/mol) is greater than that of the tilted SM molecules (−6.125 kCal/mol) and parallel orientation is the favorable orientation for adsorption. SM-SM pair interaction energy analysis also revealed that SM-SM pairs near G are more associated than SM-SM pairs in the bulk of SM. In summary, our results clearly show that G can be a good candidate for adsorption of SM and similar toxic chemical warfare agents.

Extra low friction coefficient caused by the formation of a solid-like layer: A new lubrication mechanism found through molecular simulation of the lubrication of MoS2 nanoslits

Abstract Monolayer molybdenum disulfide (MoS2) is a novel two-dimensional material that exhibits potential application in lubrication technology. In this work, molecular dynamics was used to investigate the lubrication behaviour of different polar fluid molecules (i.e., water, methanol and decane) confined in monolayer MoS2 nanoslits. The pore width effect (i.e., 1.2, 1.6 and 2.0 nm) was also evaluated. Results revealed that decane molecules exhibited good lubricating performance compared to the other two kinds of molecules. The friction coefficient followed the order of decane

What Governs Friction of Silicon Oxide in Humid Environment: Contact Area between Solids, Water Meniscus around the Contact, or Water Layer Structure?

In order to understand the interfacial parameters governing the friction force (Ft) between silicon oxide surfaces in humid environment, the sliding speed (v) and relative humidity (RH) dependences of Ft were measured for a silica sphere (1 μm radius) sliding on a silicon oxide (SiOx) surface, using atomic force microscopy (AFM), and analyzed with a mathematical model describing interfacial contacts under a dynamic condition. Generally, Ft decreases logarithmically with increasing v to a cutoff value below which its dependence on interfacial chemistry and sliding condition is relatively weak. Above the cutoff value, the logarithmic v dependence could be divided into two regimes: (i) when RH is lower than 50%, Ft is a function of both v and RH; (ii) in contrast, at RH ≥ 50%, Ft is a function of v only, but not RH. These complicated v and RH dependences were hypothesized to originate from the structure of the water layer adsorbed on the surface and the water meniscus around the annulus of the contact area. This hypothesis was tested by analyzing Ft as a function of the water meniscus area (Am) and volume (Vm) estimated from a thermally activated water-bridge formation model. Surprisingly, it was found that Ft varies linearly with Vm and correlates poorly with Am at RH < 50%; and then its Vm dependence becomes weaker as RH increases above 50%. Comparing the friction data with the attenuated total reflection infrared (ATR-IR) spectroscopy analysis result of the adsorbed water layer, it appeared that the solidlike water layer structure formed on the silica surface plays a critical role in friction at RH < 50% and its contribution diminishes at RH ≥ 50%. These findings give a deeper insight into the role of water condensation in friction of the silicon oxide single asperity contact under ambient conditions.