Non-DLVO interactions

Steric interactions are interactions between two surfaces (particles) in the presence of adsorbed macromolecules (polymers) or other molecular or particular species. Such adsorbate layers prevent the direct contact of surfaces and, thus, restrain the attractive van-der-Waals forces and can, therefore, inhibit the coagulation of 

All the same, steric interaction is related to the presence of at least one additional component (adding to continuous and dispersed phase). In that regard, it depends much more on the specific material properties than on the double layer interaction. Steric interaction is relevant for the stabilisation of colloidal suspensions with high electrolyte background or with organic solvents. A good introduction is, e.g., given by Napper (1983). 

Depletion interactions are interactions between two surfaces (particles) in the presence of firee, i.e., non-adsorbed, macromolecules, micelles, or very fine particles. Asakura and Oosawa (1954) first pointed out that if the distance between two surfaces h is smaller than the diameter of solute molecules Jm, this region will contain pure solvent depletion zone, cf. Fig. 3.14, left). Thus, an attractive force corresponding to the osmotic pressure of the bulk solution is acting on the two surfaces. Agglomeration caused by this effect is called depletion flocculation. In a second paper, the authors calculated the potential energy of this interaction for 

Several experimental studies indicate the existence of a short-ranging repulsive interaction that cannot be explained by DLVO theory or by the presence of polymers and micelles. Since it is observed in particular for hydrophilic surfaces and polar solvents, its origin is traditionally attributed to the solvation of the smface and is called solvation or hydration interaction. However, the experimental findings seem partly contradictory and the theoretical explanations are manifold. Hydration interactions are reported for different materials, e.g. latex (e.g. Healy et al.l978). 

According to Grabbe and Horn (1993), the hydration interaction decays bi-exponentially with surface distance  

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In this case, the Lewis acid-base approach has been assumed to account for all non-DLVO interactions. The exponential-decay expressions [Eq. (27)] deriving from the work of Pashley and Quirk [51], or other quantitative expressions for non-DLVO interactions, similarly could have been inserted. A major advantage of the Lewis acid-base approach is that all parameters in the expression can be determined a priori, whereas the exponential-decay... 

It is customarily assumed that the overall particle-particle interaction can be quantified by a net surface force, which is the sum of a number of independent forces. The most often considered force components are those due to the electrodynamic or van der Waals interactions, the electrostatic double-layer interaction, and other non-DLVO interactions. The first two interactions form the basis of the celebrated Derjaguin-Landau-Verwey-Overbeek (DLVO) theory on colloid stability and coagulation. The non-DLVO forces are usually determined by subtracting the DLVO forces from the experimental data. Therefore, precise prediction of DLVO forces is also critical to the determination of the non-DLVO forces. The surface force apparatus and atomic force microscopy (AFM) have been used to successfully quantify these interaction forces and have revealed important information about the surface force components. This chapter focuses on improved predictions for DLVO forces between colloid and nano-sized particles. The force data obtained with AFM tips are used to illustrate limits of the renowned Derjaguin approximation when applied to surfaces with nano-sized radii of curvature. 

Feiler, A., Jenkins, P., and Ralston, J., Metal oxide surfaces separated by aqueous solutions of linear polyphosphates DLVO and non-DLVO interaction forces, Phys. Chem. Chem. Phys., 2, 5678, 2000. 

Grasso, D., Subramaniam, K., Butkus, M., Strevett, K., and Bergendahl, J. A review of non-DLVO interactions in environmental colloidal systems. Rev. Environ. Sci. Bio/TechnoL, 1, 17, 2002. 

Many experimental studies have shown DLVO theory is not sufficient to describe particle stability in environmental systems, and additional non-DLVO interactions (hydrophobic/hydrophilic and steric) have been applied to an extended DLVO theory. The unique and size-dependent properties of nanoparticles may require additional modification of DLVO theory to model their interactions in aqueous environments. 

Significant advances have been made over the last three decades in our understanding of steric stabilization, and recently measurements have been reported on the force between two surfaces containing adsorbed polymer ". Data on the measurement of the force due to the electrostatic interaction of surfaces have also been presented, as well as those arising from non-DLVO interactions. 

Despite these efforts, no coherent theory of the non-DLVO interactions has emerged yet. The existing approaches are, in principle, based on a simple extension of DLVO interactions derived by considering the local geometry of the interacting bodies or local rather than macroscopic charge distribution. 

For INUTEC SPl, the graft polymeric surfactant based on hydrophobically modified inulin, the critical dectrolyte concentration, Cdo, that separates DLVO from non-DLVO interactions is 5 x 10 moldm [8j. The effect of the electrolyte on the electrostatic component of disjoining pressure is dearly seen, and the film thickness remains constant h =ll nm) above where steric interactions are acting. 

Non-DLVO forces also occur when the aqueous medium contains surfactants, which form micelles, or polyelectrolytes. A discussion of the complex interaction is, however, beyond the scope of this book. We recommend Ref. [199],... 

Non-DLVO colloidal interactions excluded volumes, undulation interactions, depletion forces and many-body effects... 

Non-DLVO colloidal interactions specific ion effects explained by ion-hydration forces... 

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