Polymer adhesion force involved

Jimenez-Castellanos et al. developed a method to measure both the adhesional and frictional forces involved in the attachment of such tablets to mucosa. These researchers found that a good correlation existed between the maximal adhesion strength and polymer content of the tablets tested [155]. 

The surface tension of polymers (synthetic polymers such as plastics, biopolymers such as proteins and gelatin) is indeed of much interest in many areas. In industry where plastics are used, the adhesion of these materials to other materials (such as steel, glass) is of much interest. The adhesion process is very complex since the demand on quality and control is very high. This is also because adhesion systems are part of many life-sustaining processes (such as implants, etc.). The forces involved in adhesion need to be examined, and we will consider some typical examples in the following text. 

If two such sparsely coated layers are brought into close contact, the pinned micelles from each surface interact and form novel structures. Little is known of the interactions in systems that involve both solvophobic and solvophilic (solvent-compatible) chains at low grafting densities [19,20,28]. Probing the structure and energies between these layers can yield insight into the nature of the adhesive forces between polymer-coated substrates and provide guidelines for tailoring the interactions between the interfaces. 

If adhesion mechanism is indeed the major mechanism for polymer unlubricated sliding friction, we should be able to detect various effects of surface energetics upon the friction process. On the contrary, it has been very difficult to find any clear-cut correlation. One of the reasons is that the adhesion component in itself contains more complicated viscoelastic elements of a polymer than those involved in the deformation component, as discussed in the preceding section. Another reason is that the total friction force sometimes contains a measurable deformation component especially when the counterface is rough. 

The morphology of ternary component polymer blends was shown to be related to the interfacial forces involving the components by Hobbs et al. [235]. The analysis of the interfacial forces is relevant to the concept of compatibilization by a ternary polymer additive to a binary blend. If a polymer can be chosen that exhibits good interfadal adhesion between the binary components and concentrates at the interface, improved properties can be obtained. The governing equation for determination of the resultant morphology of the ternary blend is ... 

Measurement of tensile or shear stress is the most commonly used in vitro method to determine bioadhesion. All in vitro measurements provide a rank order of bioadhesive strength for a series of candidate polymers. Measurement of tensile strength involves quantitating the force required to break the adhesive bond between the test polymer... 

In principle, an equality between the thermodynamic work of adhesion of liquid-solid systems and the work needed to separate an interface might be expected for simple systems and this has been observed for failure of adhesive-polymer interfaces bonded by van der Waals forces, (Kinloch 1987). Similarly, empirical correlations of interfacial strengths and work of adhesion values of solidified interfaces have been reported for some nominally non-reactive pure metal/ceramic systems. However, mechanical separation of such interfaces is a complex process that usually involves plastic deformation of the lattices, and hence their works of fracture are often at least ten and sometimes one hundred times larger than the works of adhesion, (Howe 1993). Nevertheless, for non-reactive metal/ceramic couples, it is now widely recognised that the energy dissipated by plasticity (and as a result the fracture energy of the interface) scales with the thermodynamic work of adhesion (Reimanis et al. 1991, Howe 1993, Tomsiaet al. 1995). 

We may now make some quantitative estimates, using plausible numbers for the physical and mechanical properties that are involved. For a fibril drawn from the adhesive of a pressure-sensitive tape, we may assume an order of magnitude for rf, of about 0.01 mm, and ryy -5 rf, i.e. about 0.05 mm. We assume the substrate to be hard, strong and smooth, and that "physical" forces act across the interface, so that AG will be of the order of 100 ergs/cm = 0.10 j/m. The shear strength of the polymer, for a practical rate of elongation, may be about 1.0 X 10 N/m ( ) or about 140 psi. Then 0.004. 

Particulate soils arise from dust, dirt, soot, hydrocarbons, metal oxides and even from hair products based on materials such as silicas or aluminas from about 1pm to less than 0.1-pm particle size see Figure 5-3. The removal of particulate soil is not controlled by the hydrophilicity of the fiber surface. Particulate soil removal depends on the bonding of the particle to the surface, the location of the particle [14], and the size of the particle. Particle size is perhaps the most critical variable for the removal of particulates. As the particle size decreases, the area of contact with the fiber increases, making it more difficult to remove from the hair. At particle sizes of less than 0.1 pm, it is very difficult to remove material from hair surfaces by ordinary shampooing [15]. When the soil particle consists of nonpolar components, its adhesion depends mainly on Van der Waals forces (e.g., waxes or polymeric resins and dimethicone polymers and the molecular size and shape are critical to their removal). Unless very high molecular weights are involved, the removal of such soils is oftentimes easier than for cationic polymers where adhesive binding includes a combination of ionic and Van der Waals forces. 

Polymers are involved in many practical adhesion problems. A polymer liquid can be present in the gap between the two media that adhere to one another in order to create strong attractive forces that strengthen the adhesion. In this context it is important to understand how polymer solutions interact with surfaces and how they create strong interactions between them [1]. The aim of this short review is to present rather qualitatively our understanding of the equilibrium thermodynamic properties of polymer solutions close to surfaces. This is clearly one of the important factors in understanding the adhesion between two surfaces mediated by polymers, but one must keep in mind that adhesion is a nonequilibrium process where energy dissipation plays a major role. This aspect will not be considered in this chapter. 

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