Adhesion bodies

Surfactants are used in many industrial applications such as agrochemicals, photochemi-cals, oil field chemicals, construction materials, food, and adhesives. Body care and cosmetics hold a 9.5% share of the market. Consumption is expected to be strongest for cosmetics and is expected to grow up to 4.8% above the overall market average... 

This chapter and the two that follow are introduced at this time to illustrate some of the many extensive areas in which there are important applications of surface chemistry. Friction and lubrication as topics properly deserve mention in a textbook on surface chemistiy, partly because these subjects do involve surfaces directly and partly because many aspects of lubrication depend on the properties of surface films. The subject of adhesion is treated briefly in this chapter mainly because it, too, depends greatly on the behavior of surface films at a solid interface and also because friction and adhesion have some interrelations. Studies of the interaction between two solid surfaces, with or without an intervening liquid phase, have been stimulated in recent years by the development of equipment capable of the direct measurement of the forces between macroscopic bodies. 

Formaldehyde, HCHO, is a primary and necessary constituent of the first five synthetic adhesives in the listing. It is a simple organic chemical first identified during the latter half of the 1800s. Its irritating and toxic odor and preservative properties were known from the time of its early development. It is a ubiquitous chemical, formed naturally in small quantities by every process of incomplete combustion as well as in normal biologic processes. The human body has a natural formaldehyde level of about 3 lg/g, ie, 3 parts per million (ppm) in the blood at all times. 

Acryhc modifiers for cement impact strength and adhesion to substrates are discussed in reference 211. Both water-soluble acryhc and acryhc emulsion polymers are used in the ceramic industry as temporary binders, deflocculants, and additive components in ceramic bodies and glazes (212) (see Ceramcs). 

In the electronics industry. Pis find wide appHcations as a dielectric material for semiconductors due to thermal stabiHty (up to 400°C) and low dielectric constant. Pis are being considered for use in bearings, gears, seals, and prosthetic human joints. The intended part can be machined or molded from the PI, or a film of PI can be appHed to a metallic part. Because of their superior adhesion, dielectric integrity, processing compatibUity, and lack of biological system impact. Pis have been used in many biological appHcations with particular success as body implants. 

The viscosity of an adhesive directly influences its penetration into a substrate as the viscosity increases, the penetrating power decreases. It also determines the amount of mileage or spread that can be obtained. An optimum viscosity exists for each substrate and each set of machine conditions and must be achieved in order to manufacture an efficient adhesive. Poly(vinyl acetate) emulsions are frequently too low in viscosity to be metered efficiently or to perform well as adhesives by themselves. They must be bodied to working viscosities, eg, by adding thickeners. 

Calcium carbonate continues to be used in its original appHcation, putty, as weU as caulks, sealants (qv), adhesives (qv), and printing inks (qv). Large volumes are used in carpet backing and in joint cements. It is used to improve body, reinforcement, and other properties. 

Wear. Ceramics generally exhibit excellent wear properties. Wear is deterrnined by a ceramic s friction and adhesion behavior, and occurs by two mechanisms adhesive wear and abrasive wear (43). Adhesive wear occurs when interfacial adhesion produces a localized Kj when the body on one side of the interface is moved relative to the other. If the strength of either of the materials is lower than the interfacial shear strength, fracture occurs. Lubricants (see Lubricants and lubrication) minimize adhesion between adj acent surfaces by providing an interlayer that shears easily. Abrasive wear occurs when one material is softer than the other. Particles originating in the harder material are introduced into the interface between the two materials and plow into and remove material from the softer material (52). Hard particles from extrinsic sources can also cause abrasive wear, and wear may occur in both of the materials depending on the hardness of the particle. 

Synthetic resins are extensively used, e.g., in surface finishes, in the fabrication and repair of boat and motor vehicle bodies, in the manufacture of laminated boards, for electrical components, in pattern making and in paints and varnishes. Non-rubber adhesives made from fish glues and from cotton derivatives (e.g. cellulose acetate) tend not to be sensitizing but, depending upon composition and the manner of use, many other types may pose significant dermatitic and fume hazards. 

When the surfaces are in contact due to the action of the attractive interfacial forces, a finite tensile load is required to separate the bodies from adhesive contact. This tensile load is called the pull-off force (P ). According to the JKR theory, the pull-off force is related to the thermodynamic work of adhesion (W) and the radius of curvature (/ ). 

In an appropriately designed experiment, it is possible to measure the pull-off force (Ps), contact radius (a versus P, ao and aj, and the separation profile outside the contact zone (D versus j ). From these measurements, it is possible to determine the thermodynamic work of adhesion between two surfaces, if the contacting bodies are perfectly elastic. 

Viscoelastic polymers essentially dominate the multi-billion dollar adhesives market, therefore an understanding of their adhesion behavior is very important. Adhesion of these materials involves quite a few chemical and physical phenomena. As with elastic materials, the chemical interactions and affinities in the interface provide the fundamental link for transmission of stress between the contacting bodies. This intrinsic resistance to detachment is usually augmented several folds by dissipation processes available to the viscoelastic media. The dissipation processes can have either a thermodynamic origin such as recoiling of the stretched polymeric chains upon detachment, or a dynamic and rate-sensitive nature as in chain pull-out, chain disentanglement and deformation-related rheological losses in the bulk of materials and in the vicinity of interface. 

Once it is recognized that particles adhere to a substrate so strongly that cohesive fracture often results upon application of a detachment force and that the contact region is better describable as an interphase [ 18J rather than a sharp demarcation or interface, the concept of treating a particle as an entity that is totally distinct from the substrate vanishes. Rather, one begins to see the substrate-particle structure somewhat as a composite material. To paraphrase this concept, one could, in many instances, treat surface roughness (a.k.a. asperities) as particles appended to the surface of a substrate. These asperities control the adhesion between two macroscopic bodies. 

Hybrids of block copolymer rubbers and acrylics have also been used to increase the low-temperature impact resistance of the adhesive used for body-side molding attachment [127]. To further enhance performance, a new type of hybrid adhesive has been developed, which combines an adhesive polymer, like an... 

Pressure-sensitive adhesives (PSAs) based on acrylic, natural rubber and silicone are employed primarily for ease of application. To name Just a few applications, PSAs bond decals to surfaces, interior decorative surfaces to interior panels, interior trim pieces in place directly or hook and loop tape for the same purpose, structural shims in place during manufacturing and acoustic (sound deadening) materials to body skin interior surfaces. Tape products with pressure-sensitive adhesive on one or both surfaces are used for such functions as cargo compartment sealing, as a fluid barrier to prevent spills and leaks in the lavatories and... 

A component or body held to another body by an adhesive. 

Human bodies are constantly exposed to a plethora of bacteria, viruses, and other inflammatory substances. To combat these infections and toxic agents, the body has developed a carefully regulated inflammatory response system. Part of that response is the orderly migration of leukocytes to sites of inflammation. Leukocytes literally roll along the vascular wall and into the tissue site of inflammation. This rolling movement is mediated by reversible adhesive interactions between the leukocytes and the vascular surface. 

The mechanical coatings are primarily barrel processed on to parts up to about 150 mm long or 400 g mass. Adhesive bonding (with a conductive adhesive to maintain the electrochemical protection by zinc) is particularly suitable for wrapping pipes. Vapour deposition has some use in products but the newest development is application on continuous strip for car-body manufacture—the surface is smooth so that the subsequently painted surface has no unevenness. 

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