Repulsion osmotic

Pigment dispersions are stabilized by charge repulsion and entropic, ie, steric or osmotic, repulsion. Although both types of stabilization force may be present in most cases, for pigment dispersions in solvent-bome coatings entropic repulsion is usually the most important mechanism for stabilization. 

A second effect is due to the local growth of adsorbed macromolecules as soon as the two protective layers begin to interpenetrate. This results in an osmotic repulsion to restore the equilibrium by diluting the macromolecules... 

Two mechanisms of steric stabilization can be distinguished entropic stabilization and osmotic repulsion. Entropic stabilization arises when two opposing adsorbed polymer layers of adjacent particles overlap, resulting in compression and interpenetration of their... 

It is postulated that the main thermodynamic driving force for particle adsorption at the liquid-liquid interface is the osmotic repulsion between the colloidal particles and hydrophilic starch polymer molecules. This leads to an effective depletion flocculation of particles at the boundaries of the starch-rich regions. At the same time, the gelatin has a strong tendency to adsorb at the hydrophobic surface of the polystyrene particles, thereby conferring upon them some degree of thermodynamic... 

Ideally, it would be desirable to be able to develop quantitative expressions for the interaction energies so that we can deal with coagulation or flocculation, at least in the case of fairly dilute dispersions, the way we did in Sections 13.3-13.4 for electrostatic stabilization. It is possible to develop approximate expressions for interaction energy due to various individual effects such as osmotic repulsion, attraction or repulsion due to the overlap of the tails of the adsorbed (or grafted) polymer layers, interaction of the loops in the layers, and so on (see Fig. 13.15). However, the complicated nature of polymer-induced interactions makes these tasks very difficult. In this section, we merely illustrate some of the issues that need to be considered in developing a fundamental quantitative understanding of polymer-induced forces. In Section... 

Alexander s treatment, the grafted brush is assumed to have a uniform segment density (step function distribution), and each chain to consist of connected semidilute blobs. The osmotic repulsion between blobs tends to stretch the chains, while the elastic free energy of the chains has the opposite effect. For a single brush, the minimization of the overall free energy with respect to the brush thickness yields the equilibrium brush thickness L0, given by... 

SI formalism and the calculations based on it above. First, there is ample evidence that the medium-range osmotic repulsion of DLVO theory is basically correct [11], A theory does not become textbook without being able to explain some phenomena well. Therefore, there must be something correct, at least to a leading approximation, about the repulsive potential... 

An increase in the osmotic pressure in the overlap region as a result of the unfavourable mixing of the A chains, when these are in good solvent conditions this is referred to as osmotic repulsion or mixing interaction, and is described by a free energy of interaction G, jx. 

Before overlap, the chains have a volume fraction (p2 and the solvent has a chemical potential //j . In the overlap region, the volume fraction of the chains is 4>2 which is higher than (p2, and the solvent has a chemical potential which is lower than nf. This is equivalent to an increase in the osmotic pressure in the overlap region. As a result, solvent diffuses from the bulk to the overlap region and the two water droplets are separated, and this results in strong repulsion the latter is referred to as mixing or osmotic repulsion. 

D. Interaction Between Surfaces, Bridging and Osmotic Repulsion... 

The equilibrium interaction between two parallel surfaces mediated by a polymer solution can be studied within the mean field approximation [34]. The polymer in the gap between the two surfaces is in equilibrium with a reservoir that fixes its chemical potential. One first determines the concentration profiles and then calculates the free energy. The interaction results from a competition between the osmotic repulsion and an attractive bridging contribution. The two contributions scale in the same way and one has to perform a complete calculation in order to determine the sign of the force. At large distances, when the two layers do not overlap, h > 2H, the force is exponentially small. At shorter distances, < h < 2H, the force per unit area is repulsive and varies as... 

An increase in the degree of ionization of blocks A leads to an increase in osmotic repulsion in the corona, and the aggregation number rapidly decreases as ... 

At the solid-water interface, terminally attached PEO will interact with water molecules and extend into the bulk aqueous medium. Using the surface force technique, Luckam (22) has observed that steric repulsion with PEO mainly occurs due to osmotic repulsion between interdigitated PEO chains. Jeon et al. (23,24) have theoretically modeled protein-surface interactions in the presence of PEO and found that steric repulsion by surface-bound PEO chains is mainly responsible for the prevention of protein adsorption on PEO-rich surfaces. 

---