Repulsive elastic force

The adhesion force increases linearly with the particle radius. Surprisingly, it is independent of the elasticity of the materials. This is because of two opposing effects. In a hard material the deformation of the solid is small. As a result the contact area and the total attractive surface energy are small. On the other hand, the repulsive elastic component is small. Both effects compensate each other. Soft materials are strongly deformed. Thus both the attractive surface energy term and the repulsive elastic term are high. 

The stabilizing factors for dispersions are the repulsive surface forces, the particle thermal motion, the hydrodynamic resistance of the medium, and the high surface elasticity of fluid particles and films. 

On the other hand, the factors destabilizing dispersions are the attractive surface forces, the factors suppressing the repulsive surface forces, the low surface elasticity, gravity, and other external forces tending to separate the phases. 

DLVO theory explained major principles of coagulation of hydrosols by electrolytes and brought to common grounds all previous observations (primarily of qualitative nature) that related to individual cases and often seemed to be contradictory. In years that followed further extensions of DLVO theory that took into account the possibility of reversible particle aggregation were developed. At very small distances between particles in addition to the usual long-range interaction, molecular attraction and electrostatic repulsion, one must account for other factors that play role at a direct particle contact. The formation of peculiarly structured hydration layers in the vicinity of solid surface, the appearance of elastic forces that are responsible for the Born repulsion between surface atoms at the point of contact, the repulsion between the adsorbed surfactant molecules in contact zone between two particles, all represent the so-called non-DLVO stability factors . This means that more or less deep primary minimum remains finite. 

The stability of a foam is determined through the interplay of a number of factors that involve bulk solution, interfacial properties, and also external forces. We have summarized some of the effects on foam stability of gravity drainage, capillary suction, surface elasticity, viscosity, electric doublelayer repulsion, dispersion force attraction, and steric repulsion. Foams are such complex systems that Lucassen (56) has stated that any attempt to understand their properties in terms of a simple all-embracing theory is doomed to failure. Nevertheless, we have attempted to provide an introduction to the occurrence, properties, and importance of foams as they relate to the petroleum industry. More detailed aspects are taken up in the subsequent chapters of this book. 

Similarly, apolar-polar repulsion between a highly charged group and very hydrophobic side chains of a chain or loop of protein would be expected to limit the freedom of rotation about backbone bonds of sufficiently kineti-cally free chain segment or loop. This increase in AG,p would decrease the number of states accessible to the polymer and decrease the entropy of the chain. The resulting development of an elastic force in the chain segment or loop of protein could be used to perform... 

The operative component of the comprehensive hydrophobic effect arises from the competition between charged and oil-like groups. This was shown to result in a previously unknown repulsive force embodied within an interaction energy called an apolar-polar repulsive free energy of hydration, AG,p. During function, AG,p works in conjunction with elastic force development by the restriction of internal chain dynamics. These have been called the hydrophobic and elastic consilient mechanisms. In Chapters 6,7, and 8, these consilient mechanisms were demonstrated to be fundamental to understanding the functions of biology s proteins. 

The energy conversions that produce motion in living organisms consist of two distinct but interlinked physical processes of hydrophobic association and elastic force development, collectively referred to as consilient mechanisms in that they each provide a common groundwork of explanation. The association of oil-like domains, hydrophobic association, has been characterized in terms of the comprehensive hydrophobic effect (CHE), and elastic force development has been described in terms of the damping of internal chain dynamics on deformation, whether deformation occurs by extension, compression or solvent-mediated repulsion (see section E.4.1.2 and Figures E.3 and E.4, below). 

But also the electroviscous effect can be seen from the same point of view. For if ionogenic groups situated at the periphery of the particle dissociate, establishing a diffuse double layer, the ionised groups attached to the structure will by mutual repulsion help to expand the particle. Thus more water can be taken in till equilibrium with the opposing elastic forces is reached at a now greater volume of the expanded particle. 

On the basis of Eqs. (11.70) and (11.74), we can determine the forces of adhesion of particles as governed not only by molecular interaction, but also by repulsion due to elastic forces. The force of adhesion with allowance for repulsion will be designated as XF this force, with Hi =H + z>0, according to [66], is equal to... 

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