Adhesives, surface properties

SFM also enables us to measure specific interaction forces between a small silicon tip and the surface. The pull-off forces between the tip and the surface estimated from Force vs Distance Curves (FDC) can be correlated to the adhesive interactions between tip and surface [9]. Recording of FDCs line-by-line allows us to image surface topography and adhesive surface properties simultaneously [10]. This technique has some disadvantages, like the requirement for a large amount of data acquisition and analysis, which have been alleviated by the invention of the Pulsed Force Mode (PFM). The PFM simplifies and accelerates the measurements of adhesive properties with high lateral resolution [11, 12]. 

Another interesting polymer is known as PTFE - poly(tetrafluoroethene). It has distinctive non-adhesive surface properties, and is widely used in non-stick pans under registered trademark names such as Teflon . It also comprises one of the layers in the manufacture of waterproof and breathable fabrics such as Gore-tex . 

The exceUent adhesion to primed films of polyester combined with good dielectric properties and good surface properties makes the vinyhdene chloride copolymers very suitable as binders for iron oxide pigmented coatings for magnetic tapes (168—170). They perform very weU in audio, video, and computer tapes. 

Another example of static SIMS used in a more quantitative role is in the analysis of extmded polymer blends. The morphology of blended polymers processed by extrusion or molding can be affected by the melt temperature, and pressure, etc. The surface morphology can have an effect on the properties of the molded polymer. Adhesion, mechanical properties, and physical appearance are just a few properties affected by processing conditions. 

Melamine (I,3,5-triamino-2,4,6-triazine) was first prepared by Liebig in 1835. For a hundred years the material remained no more than a laboratory curiosity until Henkel patented the production of resins by condensation with formaldehyde. Today large quantities of melamine-formaldehyde resins are used in the manufacture of moulding compositions, laminates, adhesives, surface coatings and other applications. Although in many respects superior in properties to the urea-based resins they are also significantly more expensive. 

There are numerous techniques which provide information related to the surface energy of solids. A large array of high-vacuum, destructive and non-destructive techniques is available, and most of them yield information on the atomic and chemical composition of the surface and layers just beneath it. These are reviewed elsewhere [83,84] and are beyond the scope of the present chapter. From the standpoint of their effect on wettability and adhesion, the property of greatest importance appears to be the Lifshitz-van der Waals ( dispersion) surface energy, ys. This may be measured by the simple but elegant technique of... 

A chemical property of silicones is the possibility of building reactivity on the polymer [1,32,33]. This allows the building of cured silicone networks of controlled molecular architectures with specific adhesion properties while maintaining the inherent physical properties of the PDMS chains. The combination of the unique bulk characteristics of the silicone networks, the surface properties of the PDMS segments, and the specificity and controllability of the reactive groups, produces unique materials useful as adhesives, protective encapsulants, coatings and sealants. 

Even the void fraction together with particle size distribution does not provide all of the necessary information on the kind of flow. The mutual forces between distinct particles depend not only on the distance between the particles but also on the surface properties of the particles. The strength of the attractive forces between particles depends on conditions. For instance, the moisture content of the solid is essential for determining the attractiv c forces between particles, especially for hydroscopic materials such as wood. Airflow between particles usually tends to separate particles, whereas the surface forces, adhesion forces, tend to bring them together. 

Electron beam-initiated modification of polymers is a relatively new technique with certain advantages over conventional processes. Absence of catalyst residue, complete control of the temperature, a solvent-free system, and a source of an enormous amount of radicals and ions are some of the reasons why this technique has gained commercial importance in recent years. The modification of polyethylene (PE) for heat-shrinkable products using this technique has been recently reported [30,31]. Such modification is expected to alter the surface properties of PE and lead to improved adhesion and dyeability. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

Majumder and Bhowmick [381] have investigated the influence of the concentration of TMPTA on the surface properties of EPDM mbber, modified in the presence of EB. The surface energy of the TMPTA-modified EPDM mbber has been observed to increase as compared to the unmodified one. Table 31.4 displays the contact angles and the work of adhesion of water, for the control and the modified EPDM surfaces. 

Nature takes various approaches to adhesion, the most common being to control contact area through deformation of a multitude of hairlike fibrils or alternatively to modify the surface property in a way analogous to chemical force microscopy. These processes have been... 

Adhesion of non-polar polymers is sometimes improved by oxidation, so essentially what is normally thought of as degradation may be used to introduce an enhancing surface property. Nevertheless, in both cases the oxidation process modifies the polymer surfaces, and the analysis tools can be rather similar, see, e.g., Ref. [101]. 

What one considers included in surface properties depends on what one considers the surface. (We are not in this chapter considering specific coatings per se that may be applied to achieve a particular effect or property). For adhesion... 

Friedman, L. I., Liem, H., Grabowski, E. F., Leonard, E. F., and McCord, C. W., Inconsequentiality of surface properties for initial platelet adhesion. Transactions— American Society for Artificial Internal Organs 16, 63-73 (1970). 

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