Interfacial adhesion force

NR/modified EPDM, in which EPDM was modified by pendant sulfur, exhibited improved endurance to repeated stress over that of covulcanized EPDM-NR mbber blends (68). The effects of ethylene and diene contents in EPDM, blend ratio, dicumyl peroxide curing system on the physical properties, interfacial adhesion force, and dynamic crack growth were examined (69). As the ethylene and diene contents in EPDM increased, the physical properties, such as dynamic cut growth, adhesion to other component were also increased. The mechanical properties of the blends are compared to those of the pure components in Table 15.3 (56). The ultimate tensile strength of noncompatibilized blends is lower than that of pure NR, as expected since these blends are incompatible. 

Additional applications of in situ TEM include in situ measurement of the interfacial adhesive forces in nanoparticles and biological samples [51],... 

When an aerosol particle impacts on a surface, there is an interfacial adhesion force attempting to hold them together. When the adhesion force is... 

The Webster definition of adhesion is simply the molecular attraction exerted between the snrfaces of bodies in contact (7). In the more technical world, it is understood that there are many complex components to adhesion in a system, both chemical and physical. Further, the wide variety of complex combinations limits the merit of general predictive mles of thumb. Instead, perhaps, it is useful to simply let a specific situation define an appropriate adhesion test, and thus the practically adherent system. A sufficiently adherent interface is one in which the appropriate applied load or sttess did not exceed the total interfacial adhesive forces. Stresses in coated systems can be either compressive or tensile when experienced normal to the surface, shearing when in a parallel orientation, or some combination of these. Much can be learned from automotive adhesion requirements, because so many durable coating applications in so many situations are found in this industry. Table 7 summarizes some of the tests used to measure adhesion. The following sections offer summaries of important aspects of adhesion in practical coating systems. 

The interfacial free energy per unit area is given by the adhesion force Fo/lrR", estimate the Hamaker constant responsible for the adhesion force in the crossed-cylinder geometry illustrated in the inset to Fig. VI-6. 

Dutrowski [5] in 1969, and Johnson and coworkers [6] in 1971, independently, observed that relatively small particles, when in contact with each other or with a flat surface, deform, and these deformations are larger than those predicted by the Hertz theory. Johnson and coworkers [6] recognized that the excess deformation was due to the interfacial attractive forces, and modified the original Hertz theory to account for these interfacial forces. This led to the development of a new theory of contact mechanics, widely referred to as the JKR theory. Over the past two decades or so, the contact mechanics principles and the JKR theory have been employed extensively to study the adhesion and friction behavior of a variety of materials. 

Israelachvili and coworkers [64,69], Tirrell and coworkers [61-63,70], and other researchers employed the SFA to measure molecular level adhesion and deformation of self-assembled monolayers and polymers. The pull-off force (FJ, and the contact radius (a versus P) are measured. The contact radius, the local radius of curvature, and the distance between the surfaces are measured using the optical interferometer in the SFA. The primary advantage of using the SFA is its ability to study the interfacial adhesion between thin films of relatively high... 

Adhesion — (a) When two compact materials, be they solid or liquid, are in intimate contact, attractive forces may act between their surface atoms or molecules. These forces are typically - van der Waals forces and electrostatic forces. The work of adhesion W (b)b(a) between the two phases (denoted A and B) is WAB = yA+yB -yAB> where yA and yg are the - interfacial tensions of A and B when each is interfaced only with the vapor phase, and yAB is the interfacial tension of the interface between A and B. In a more rigorous treatment (at thermodynamic equilibrium) each phase is regarded as saturated with the other phase [i]. In the case of liquid phases the equation for the work of adhesion is referred to as the -> Dupre equation. Adhesion forces between particles, or between particles and surfaces, dominate gravity for small particle sizes (pm and sub-pm range). In electrochemistry, increasing attention is being given to various phenomena related to the adhesion of vesicles [ii], particles [iii], droplets [iv], cells [v], etc. to electrode surfaces. 

Aqueous film stability is dependent on the adhesive force or negative interfacial tension at the two-phase (i.e., solid/liquid) boundary. The force balance at the two-phase boundary may change independently from the three-phase force balance due to surface configuration change of interfacing surface state moieties, which occurs in order to minimize interfacial tension with water as described in previous chapters. 

The contact angle 0 depends on the balance between the sohd/Vapour (ygy) and solid/liquid (yg ) interfacial tensions. The angle which a drop assumes on a solid surface is the result of the balance between the adhesion force between solid and liquid and the cohesive force in the liquid,... 

Problem 2-29. Interfacial Tension-Capillary Effects. A rigid sphere of radius a rests on a flat surface, and a small amount of liquid surrounds the point of contact, making a concave-planar lens whose diameter is small compared with a. The angle of contact 9C with each of the solid surfaces is zero (see Problem 2-28), and the tension in the air-liquid surface is a. Show that there is an adhesive force of magnitude Anaa acting on the sphere. (The fact that this adhesive force is independent of the volume of liquid is noteworthy. Note also that the force is repulsive when 9C = n.)... 

The physically active sites of carbon black should produce an increase in interfacial adhesion and hence an increase in reinforcement. Furthermore, this increase in reinforcement should be non-specific for different non-polar polymers, since it still reflects a dispersion force interaction. While its existence cannot be questioned, it clearly cannot be assumed to be responsible for the entire observed increase in reinforcement over and above that displayed by graphitized carbon black if other, more energetic bonds are also formed. 

At the same time, liquid medium of a similar nature as well as the adsorption of surfactants may lower the interfacial energy, a, and complex Hamaker constant, A, by 2 - 3 or more orders of magnitude. In such lyophilized system the adhesion forces and energy are lowered by several orders of magnitude [17]. Under these conditions a system with low concentration of dispersed phase remains stable towards aggregation (see... 

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