The presence of leachable alkali ions, or their hydrated sites in the glass, is believed to be a determining factor for the interfacial water structure at the glass surface, influencing the surface properties of glass. The interfacial water structure on soda‐lime silicate glass in humid ambience at room temperature was analyzed with sum‐frequency‐generation (SFG) vibration spectroscopy, which can probe the interfacial water layer without spectral interferences from the gas phase water. The soda‐lime glass surface exposed to water vapor shows three sharp SFG peaks at 3200, 3430, and 3670 cm−1 in SFG, which is drastically different from the SFG spectra of the water layers on the fused quartz glass surface and the liquid water/air interface. The sharp peak at 3200 cm−1 is believed to be associated with the hydronium ions in the Na+‐leached silicate glass surface. The 3200 cm−1 peak intensity varies with the relative humidity, indicating its equilibrium with the gas phase water. It is proposed that the hydronium ions in the Na+‐leached sites produce compressive stress in the silicate glass surface; thus the growth of hydronium ions with increasing humidity might be responsible for the increased wear resistance of soda‐lime glass surfaces in near‐saturation humidity conditions.

The effects of physisorbed organic vapor molecules on friction and wear were studied for various materials with different surface chemistries (metals, ceramics, glasses, carbons, polymers) and adsorbed species with distinct functional groups (short linear-chain, branched, and fluorinated alcohols with alkyl chain lengths up to five carbons as well as acetone and n-decane). Friction test results of stainless steel under equilibrium vapor adsorption conditions indicated that the longer chain length of the adsorbed alcohols results in lower friction and that n-pentanol gives the lowest friction and wear among the molecules investigated. The adsorption isotherm measurements revealed that the functional groups of the adsorbed molecules appear to play important roles in lubrication. Friction coefficients that ranged from 0.02 to 0.9 for the various materials in dry and humid environments converged to ∼0.15 for the inorganic solid materials tested in n-pentanol. These findings indicate that the molecular lubrication by the physisorbed species dominates the tribological behaviors of the inorganic solid materials, regardless of bulk mechanical properties. Tribotests using polymeric materials did not show the same lubricating effects for n-pentanol vapor. The failure of n-pentanol to lubricate polymeric materials may be due to vapor ingress into the polymer and the absence of an adsorbed surface layer.

The mechanochemical reactions of adsorbed molecules at sliding interfaces were studied for αpinene (C 10 H 16), pinane (C 10 H 18), and n-decane (C 10 H 22) on a stainless steel substrate surface. During vapor phase lubrication, molecules adsorbed at the sliding interface could be activated by mechanical shear. Under the equilibrium adsorption condition of these molecules, the friction coefficient of sliding steel surfaces was about 0.2 and a polymeric film was tribochemically produced. The synthesis yield of α-pinene tribo-polymers was about twice as much as pinane tribo-polymers. In contrast to these strained bicyclic hydrocarbons, n-decane showed much weaker activity for tribo-polymerization at the same mechanical shear condition. These results suggested that the mechanical shear at tribological interfaces could induce the opening of the strained ring structure of -pinene and pinane, which leads to polymerization of adsorbed molecules at the sliding track. On a stainless steel surface, such polymerization reactions of adsorbed molecules do not occur under typical surface reaction conditions. The mechanical properties and boundary lubrication efficiency of the produced tribo-polymer films are discussed.

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The adsorption of vapor molecules plays an important role in countless fields and is increasingly realized to be critical in tribology, which encompasses adhesion, friction, and wear of surfaces. This feature article reviews experimental methods for quantifying gas and vapor adsorption on flat solid surfaces under equilibrium conditions (ambient pressure and temperature) as well as the effects of these adsorbates on the adhesion, friction, and wear of various materials. Particular attention is given to species that are present in the ambient environment such as water (humidity) and organic vapors. These adsorbed species can have drastic yet varied influences on tribology depending on the surface chemistry of materials. Despite prolonged and ubiquitous observations in a broad range of materials and vapors, a fundamental understanding of the effect of adsorbed gases and vapors on the adhesion, friction, and wear of surfaces has begun only recently through surface-sensitive characterization.

Tribology involves not only two-body contacts of two solid materials-a substrate and a counter-surface; it often involves three-body contacts whether the third body is intentionally introduced or inevitably added during the sliding or rubbing. The intentionally added third body could be lubricant oil or engineered nanomaterial used to mitigate the friction and wear of the sliding contact. The inevitably added third body could be wear debris created from the substrate or the counter surface during sliding. Even in the absence of any solid third-body between the sliding surfaces, molecular adsorption of water or organic vapors from the surrounding environment can dramatically alter the friction and wear behavior of solid surfaces tested in the absence of lubricant oils. This review article covers the last case: the effects of molecular adsorption on sliding solid surfaces both inevitably occurring due to the ambient test and intentionally introduced as a solution for engineering problems. We will review how adsorbed molecules can change the course of wear and friction, as well as the mechanical and chemical behavior, of a wide range of materials under sliding conditions.

Although samples are visibly clean, organic deposits could have tremendous impacts on tribological measurements and interpretation of friction and wear behaviors. This paper discusses the boundary lubrication effects of invisible residues from organic solvents that have been widely used in tribological studies in ambient conditions. Stainless steel, soda lime glass, and copper substrates were cleaned using UV/ozone treatment or organic solvents such as alcohols where the solvent was allowed to evaporate from the surface. In ball-on-flat tribo-tests, all UV/ozone cleaned samples showed high friction and catastrophic wear immediately upon sliding due to the absence of lubricants at the sliding interface, while samples cleaned by organic solvent experienced low friction and minimal wear for hundreds of reciprocating cycles. Analyses of the surface by atomic force microscopy and vibrational spectroscopy indicated that the solvent cleaning deposits hydrocarbon residue on metal and oxide substrates. This residue is due to trace impurities with low vapor pressures inevitably present in the bulk liquid, regardless of solvent

Friction initially occurs in a vapor environment, during which a triboproduct is formed. This triboproduct lubricates in absence of the vapor for over 30 000 reciprocating cycles.