Surface Adhesion Water Wettability

The surface wettability by water drops has been clearly linked with the concentration of chemically bound nitrogen in the surface. Conversely, measurements of advancing and receding contact angles for water can provide information regarding surface composition. On the other hand, there appears to be little or no direct correlation between water wettability and adhesive strength of evaporated aluminum films. Substantial improvement in adhesion of Ai to many polymers can be achieved by 02 plasma treatment of the polymer surface before metallization. Other workers have shown this to result in chemical linkages between the metal and polymer surface moieties. 

Chem. Descrip. Surface-modified particulate rubber Uses Additive which reduces costs, improves adhesion, enhances composite performance in urethane foam, cast wheels and rollers, nonpneumatic tires, coatings, linings, adhesives, shoe soles Properties BIk. free-flowing powd. 150 p on 100 mesh sp.gr. 1.10-1.15 bulk dens. 24-28 Ib/ft surf, energy 55+ dynes/cm (water wettable) 1% moisture... 

The contact angle was measured on planed lamellas before bonding in order to determine the wettability of the wood surface with water and with the PF adhesive. The sessile drop method was used to measure the contact angle of a drop deposited... 

Roll-up mechanism [Figure 18.1(a)]—when the surface-active agent dispersed in a displacement liquid adsorbs at the solid-water interface, the wettability of the solid surface for water decreases and the area of contact becomes so small that buoyant forces overbalance the adhesion forces and finally cause water droplets to be released. 

Many novel high-performance soft contact lenses contain siloxane backbones because of the high oxygen transmissibility DJL) provided by such a chemistry [12]. The ocular environment remains healthier with siloxane-based lens materials. However, siloxane molecules are not inherently water wettable because of their low critical surface tensions [llj. In addition, siloxane surfaces attract lipid-soluble material, which can penetrate the lens [16]. Siloxane-based lenses can also attract and attach proteins and mucus on the surface of the lens [16]. The physical and chemical changes in the lens surface and bulk associated with deposit formation include tear film disruption, decreased vision, discomfort, decreased lens life, conjunctival hyperemia, and bacterial adhesion [17,18]. 

On the other hand, perfluorinated polymers likepoly(tetrafluoroethylene), (PTFE), as one of the most important examples, represent a polymer class which is in particular characterized by its special surface and adhesion properties. Perfluorinated segments in polymers often result in strongly nonpolar surfaces with reduced wettability of water or organic molecules, reduced adhesion and yielding, excellent gliding, and antisticking properties, and, in particular, chemical inertness [13,14]. 

One of the most common rubber adhesives are the contact adhesives. These adhesives are bonded by a diffusion process in which the adhesive is applied to both surfaces to be joined. To achieve optimum diffusion of polymer chains, two requirements are necessary (1) a high wettability of the adhesive by the smooth or rough substrate surfaces (2) adequate viscosity (in general rheological properties) of the adhesive to penetrate into the voids and roughness of the substrate surfaces. Both requirements can be easily achieved in liquid adhesives. Once the adhesive solution is applied on the surface of the substrate, spontaneous or forced evaporation of the solvent or water must be produced to obtain a dry adhesive film. In most cases, the dry-contact adhesive film contains residual solvent (about 5-10 wt%), which usually acts as a plasticizer. The time necessary... 

The contact angles of water and adhesive resin on wood are higher in the case of freshly harvested wood compared to stored chips. This means that the surface of particles from this fresh wood is more hydrophobic. This influences the wetting and the penetration negatively and with this the gluability. Reason for this lower wettability of freshly harvested wood is a higher content of some wood chemical components, or wood extractives, as has been determined by water extraction. This result, however, must not be confused with the better wettability of a freshly cut surface, independently if it is freshly harvested or stored wood. 

In general, grafting of hydrophillic monomers have been found to lead to an increase in wettability, adhesion, dyeing, and rate of release of oil stains by detergent solution. On the other hand, if the monomer is hydro-phobic, the result will be decreased wetting by all liquids including oil stains. If grafting is not restricted to surface alone but encompasses the bulk of the backbone polymer, then the properties such as flame resistance, water sorption, crease resistance, etc. will be affected. 

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