Water adhesive displacement

The failure of the interfaee between the resin and the wood surfaee (replacement of physieal bondings between resin and reaetive wood surfaee sites by water or other nonresin ehemieals). The adhesion of UF resins to eellulose is sensitive to water not only due to the already mentioned lability to hydrolysis of the methylene bridge and of its partial reversibility, but also beeause theoretical calculations have shown that on most eellulose sites the average adhesion of water to eellulose is stronger than that of UF oligomers [8,48]. Thus, water can displace hardened UF resins from the surface of a wood joint. The inverse effect is valid for PF resins [8,49]. 

The rate of diffusion of water in an adhesive is important if water can displace the adhesive from its substrate, or if there is appreciable solubility, for this determines its rate and pattern of saturation. Where the adherend itself absorbs moisture, as does wood, the rate of diffusion through the adhesive from one adherend to the other may be of importance in minimizing stresses arising from incipient dimensional changes. A full account of the method for calcidating the pattern of distribution of water in an adhesive joint is given by Althof (1981) and also by Comyn (1981). Both these authors also consider the effect of absorbed water and the pattern of its distribution on the properties of the joint. The maximum stresses in a lap-shear joint are at the ends of the overlaps and, of course, since here in one of the boundary surfaces for the entry of moisture the moisture first attains moisture equilibrium at the position of maximum stress. This results in a reduction of the... 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

Qnantized adhesion was observed by Hoh et al. [53] for a SisN4 tip breaking contact with a glass snrface in water, which had been NaOH adjusted to pH 8.5. As described at the beginning of Section IILA, a more accurate description of the measurement would be quantized displacement, which can be evaluated as quantized adhesion by multiplying the observed displacement by the lever stiffness. The authors speculate that their observations conld be explained either by the breaking of discrete numbers of hydrogen bonds between the tip and surface or by the breakdown of the continuum properties of water in close proximity to a solid surface. 

Figure 4c shows that the amount of adsorbed proteins is rapidly saturated within several minutes of exposing serum-containing medium to a surface. Albumin, the most abundant serum protein, was expected to preferentially adsorb onto the surfaces during early time points. Then, adsorbed albumin was expected to be displaced by cell adhesion proteins. To investigate the effect of preadsorbed albumin displacement on cell adhesion, SAMs were first exposed to albumin then, HUVECs suspended in a serum-supplemented medium were added [21, 42]. Very few cells adhered to hydrophobic SAMs that had been pretreated with albumin, due to the large interfacial tension between water and the hydrophobic surfactant-like surface. Albumin was infrequently displaced by the cell adhesive proteins Fn and Vn. One the other hand, HUVECs adhered well to hydrophilic SAM surfaces that had been preadsorbed with albumin. In that case, the preadsorbed albumin was readily displaced by cell adhesive proteins. 

We have discussed the positive effects that bacterial displacement and adhesion to substrates exerts on the diffusive mass transfer. Theoretically, direct contact with the substrate could also allow microorganisms to employ other modes of uptake in addition to absorption of water-dissolved molecules. So, which are the physical states for which chemicals can be ingested by microorganisms ... 

The interfacial chemistry of corrosion-induced failure has also been studied for coatings with relatively poor resistance to water (poor wet adhesion) for these materials, the corrosion-induced failure typically involved little chemical change, but appeared to involve the same displacement mechanism observed for hvunidity induced adhesion loss (19). XPS spectra showing this mode of failure are reproduced in Figure 1 for this coating, essentially identical spectra were obtained from all surfaces analyzed, independent of test conditions. 

Displacement of epoxy by water definitely plays an important role in the strength loss of metal/epoxy adhesion systems. However, there are also other mechanisms by which water can reduce the strength of the interfacial region. 

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