Coagulation contacts rheology

In structured disperse systems with coagulation contacts between particles the viscosity undergoes a much more abrupt change. In this case one may outline a broad spectrum of different states that fall in between the two extreme cases fully structured systems and systems with totally destroyed structure. Depending on the magnitude of applied shear stress (flow rate), the rheological properties of structured disperse systems may change from those... 

For situations i) and ii) the coagulated state, i.e. with the particles in intimate contact, is desirable. For other purposes, the flocculated state is required, i.e. with the particles still essentially individual and separated by a thin layer of liquid, thus giving control of the rheological properties of the sytem. Frequently, the secondary minimum plays a significant role in flocculated systems. 

The second study focuses on the summation of the contact interactions using the estimation of the rheological parameters of a coagulation structure formed with substantially anisometric particles (fibers) [29]. 

Physical-Chemical Mechanics of Disperse Systems and Materials contains seven chapters. Section I, with four chapters, presents the basics, starting from surface forces and the contact of particles with liquids. Chapter 2 is dedicated to adsorption phenomena, accumulation of surface-active molecules at various interfaces, and the importance of surfactant s adsorption on the contact between particles. The bulk properties of particle dispersions in liquids are discussed in Chapter 3 in terms of coagulation processes and the rheological behavior. Chapter 4 describes in a comprehensive way the stability of disperse systems and emphasizes the Rehbinder effect as an important mechanism in stable colloidal systems. Section II consists of three chapters. Chapter 5 provides an introduction to the methodology of mechanical testing Chapter 6 describes in detail the structures... 

We know that Va is inversely proportional to d, whereas Vr decreases exponentially with the distance 2d. Thus, at short and long distances of d, Va becomes larger than Vr, but at intermediate distances the two particles repel each other strongly due to the repulsion of Bom and Mayer. Thus, Vt has two minima, as shown in Fig. 7.7 a deep one at a short interparticle distance and a shallow one at a relatively long interparticle distance. Coagulation takes place at the first deep minimum. The secondary minimum plays an important role for plate- or rod-like particles that have a wide interparticle contact area. However, because the second minimum is relatively shallow, the coagulation induced by it is easily broken by an external force. This effect is closely related to rheological phenomena of colloidal suspensions. 

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