Colloidal forces DLVO theory

Colloidal forces DLVO theory Surface forces... 

Surface forces Colloidal forces DLVO theory Definition... 

Colloid stability depends significantly on the (often) attractive van der Waals forces and the (often) repulsive electric and steric forces. DLVO theory accounts for the van der Waals and electric forces and these are the ones which are discussed in this chapter. The main... 

The well-known DLVO theory of coUoid stabiUty (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the Hquid—soHd interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobiUty or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see Colloids). 

The DLVO theory [88,89], a landmark in the study of colloids, interprets stability as dependent on the competition between the long-range repulsion forces of similarly charged... 

At short interparticle distances, the van der Walls forces show that two metallic particles will be mutually attracted. In the absence of repulsive forces opposed to the van der Walls forces the colloidal metal particles will aggregate. Consequently, the use of a protective agent able to induce a repulsive force opposed to the van der Walls forces is necessary to provide stable nanoparticles in solution. The general stabihzation mechanisms of colloidal materials have been described in Derjaguin-Landau-Verway-Overbeck (DLVO) theory. [40,41] Stabilization of colloids is usually discussed... 

The physicochemical forces between colloidal particles are described by the DLVO theory (DLVO refers to Deijaguin and Landau, and Verwey and Overbeek). This theory predicts the potential between spherical particles due to attractive London forces and repulsive forces due to electrical double layers. This potential can be attractive, or both repulsive and attractive. Two minima may be observed The primary minimum characterizes particles that are in close contact and are difficult to disperse, whereas the secondary minimum relates to looser dispersible particles. For more details, see Schowalter (1984). Undoubtedly, real cases may be far more complex Many particles may be present, particles are not always the same size, and particles are rarely spherical. However, the fundamental physics of the problem is similar. The incorporation of all these aspects into a simulation involving tens of thousands of aggregates is daunting and models have resorted to idealized descriptions. 

The DLVO theory, a quantitative theory of colloid fastness based on electrostatic forces, was developed simultaneously by Deryaguin and Landau [75] and Verwey and Overbeek [76], These authors view the adsorptive layer as a charge carrier, caused by adsorption of ions, which establishes the same charge on all particles. The resulting Coulombic repulsion between these equally charged particles thus stabilizes the dispersion. This theory lends itself somewhat less to non-aqueous systems. 

To what extent can theory predict the collision efficiency factor Two groups of researchers, Derjagin and Landau, and Verwey and Overbeek, independently of each other, have developed such a theory (the DLVO theory) (1948) by quantitatively evaluating the balance of repulsive and attractive forces that interact most effective tool in the interpretation of many empirical facts in colloid chemistry. 

The pair potential of colloidal particles, i.e. the potential energy of interaction between a pair of colloidal particles as a function of separation distance, is calculated from the linear superposition of the individual energy curves. When this was done using the attractive potential calculated from London dispersion forces, Fa, and electrostatic repulsion, Ve, the theory was called the DLVO Theory (from Derjaguin, Landau, Verwey and Overbeek). Here we will use the term to include other potentials, such as those arising from depletion interactions, Kd, and steric repulsion, Vs, and so we may write the total potential energy of interaction as... 

In the past decade, much development has taken place in regard to measuring the forces involved in these colloidal systems. In one method, the procedure used is to measure the force present between two solid surfaces at very low distances (less than micrometer). The system can operate under water, and thus the effect of addictives has been investigated. These data have provided verification of many aspects of the DLVO theory. Recently, the atomic force microscope (AFM) has been used to measure these colloidal forces directly (Birdi, 2002). Two particles are brought closer, and the force (nanoNewton) is measured. In fact, commercially available apparatus are designed to perform such analyses. The measurements can be carried out in fluids and under various experimental conditions (such as added electrolytes, pH, etc.). 

Kruyt, H. R. (Ed.), Colloid Science. Vol. 1. Irreversible Systems, Elsevier, Amsterdam, Netherlands, 1952. (Graduate and undergraduate levels. A classic reference on colloids. Chapters 6-8, by Professor J. Th. G. Overbeek, present the classical DLVO theory of colloidal forces and their application to kinetics of coagulation.)... 

In the 1950s. the DLVO theory was based largely upon forces 11) and (2i defined above. The DLVO theory became the basts for studying the properties of colloidal and biocolloidal systems. 

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

The DLVO-theory is named after Derjaguin, Landau, Verwey and Overbeek and predicts the stability of colloidal suspensions by calculating the sum of two interparticle forces, namely the Van der Waals force (usually attraction) and the electrostatic force (usually repulsion) [19],... 

In several cases, however, the DLVO-theory has shown to be inadequate, due to the occurrence of other inter-particle forces that may be present in colloidal suspensions. These phenomena are summed up below ... 

When two charged particles immersed in an electrolyte approach each other, the overlap of their ionic atmospheres (the double layers) generates a repulsive force. The traditional Derjaguin—Landau—Verwey—Overbeek (DLVO) theory assumes that the stability of charged colloids is a consequence of a balance between this double layer repulsion and the attractive van der Waals interactions.1... 

When either ion-hydration interaction or ion-dispersion forces were included in the treatment, the results were qualitatively identical to the traditional DLVO theory, which roughly predicts that strongly charged colloidal particles are stable, and weakly charged particles coagulate. Significant quantitative differences, which can account for specific ion effects, could he introduced by either mechanism, when suitable interaction parameters were selected. 

In fact, the SFA was initially developed for practically probing the DLVO theory, and DLVO forces were successfully measured in electrolyte solutions and colloidal systems [4,22]. However, the applications of the apparatus were not restricted to this. Detailed and accurate information was obtained on thickness and refractive index profiles of thin films [6], simple liquid molecular structuring... 

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