Colloids depletion flocculation

Jenkins P and Snowden M 1996 Depletion flocculation in colloidal dispersions Adv. Colloid Interface Sc/. 68 57-96... 

Vincent, B., Edwards, J., Emmett, S. and Jones, A. (1986) Depletion flocculation in dispersions of sterically-stabilised particles (soft spheres). Colloids Surf,... 

In the case of biopolymer molecules residing in the space between colloidal particles or droplets, the force associated with the deep energy minimum at contact is often referred to as the depletion force because the intervening biopolymer species are depleted from the narrow gap between the pair of neighbouring particles. This attractive interparticle interaction underlies the phenomenon of reversible depletion flocculation in oil-in-water emulsions (see equation (3.41) in chapter 3). 

Radford, S.J., Dickinson, E. (2004). Depletion flocculation of caseinate-stabilized emulsions what is the optimum size of the non-adsorbed protein nano-particles Colloids and Surfaces A Physicochemical and Engineering Aspects, 238, 71-81. ... 

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... 

Manoj, P., Fillery-Travis, A.J., Watson, A.D., Hib-berd, D.J., and Robins, M.M. 1998. Characterization of depletion-flocculated polydisperse emulsion I. Creaming behavior. J. Colloid Interface Sci. 207 283-293. 

It is well known that the presence of an excess of nonadsorbed polymer can result in flocculation of colloidal particles by the so-called depletion flocculation mechanism [13], In the clay-PEO system, the excess PEO molecules in the supernatant fluid would exert an osmotic pressure on the gel, and the effect should be similar to that of applying an external pressure to the gel indeed, because the... 

Increased depletion attraction. The presence of nonadsorbing colloidal particles, such as biopolymers or surfactant micelles, in the continuous phase of an emulsion causes an increase in the attractive force between the droplets due to an osmotic effect associated with the exclusion of colloidal particles from a narrow region surrounding each droplet. This attractive force increases as the concentration of colloidal particles increases, until eventually, it may become large enough to overcome the repulsive interactions between the droplets and cause them to flocculate (68-72). This type of droplet aggregation is usually referred to as depletion flocculation (17, 18). 

Rawson, S. Ryan, K. Vincent, B. Depletion flocculation in sterically stabilized aqueous systems using poly electrolytes. Colloids and Surfaces 1988, 34, 89-93. 

The presence of polymers, either adsorbed on colloidal particles or free in solution, can lead to other interesting effects. For example, if a high-molecular-weight polymer is present at low concentration, remote segments of a polymer chain may be adsorbed on separate particles, causing them to be drawn together (bridging flocculation). The presence of an excess of non-adsorbed polymer can also result in flocculation (depletion flocculation). These and other special cases will be discussed in Chapter 9. 

The Effects of Free Polymer on Colloid Stability Theories of Depletion Flocculation and Depletion Phase Separation... 

In the foregoing chapters the effects of attached polymer chains on colloid stability have been set forth. We now turn to consider the effects of macromolecules that are not attached to the particles but rather are free in solution. Surprisingly, such free polymer is still able to affect colloid stability, being capable of generating both stability and flocculation. Stability that is imparted by free polymer is termed depletion stabilization. Aggregation that is induced by free polymer is called depletion flocculation. The latter will be discussed in this Chapter, consideration of depletion stabilization being postponed until the next Chapter. 

If one adds a polymer that is not adsorbed or poorly adsorbed on the particles to a colloidal solution, there may occur another phenomenon, termed depletion flocculation. In depletion flocculation, as two particles approach, polymer chains that are weakly adsorbed, or simply are located between the particles, become squeezed out of the area of closest approach, leaving bare surfaces that are attracted in the normal way. However, there may arise an additional attractive force as a result of the removal of polymer from the intervening region (Fig. 10.12). 

In the presence of poly(styrene sulphonate) at 40 C the particles flocculate as a consequence of depletion forces operative in the system. It is believed that the polymer does not adsorb onto the particles from water at neutral pH as both species have negative charges. Other hard sphere colloids have been reported to undergo similar depletion flocculation processes with poly(styrene sulphonate) (2,6) under similar conditions but at a fixed temperature. The flocculated latex on cooling down to 25 C redisperses, as a consequence of the particles swelling with solvent and then undergoing conformational rearrangments. The soft nature of the particles at 25 C... 

Fig. 3.14 Depletion interaction between two particles in the presence of a non-adsorbing colloidal species (e.g. nanoparticles, polymers, micelles) depletion flocculation (left) for low colloid concentrations and depletion stabilisation (right) for large ones...

In Sects. 1.2.1 and 1.2.2 we shall first qualitatively consider double layer and Van der Waals interactions, the two contributions to the DLVO potential (Sect. 1.2.3), and then discuss (polymeric) steric stabilization by end-attached polymer in Sect. 1.2.4. While not further discussed here we mention that adsorbing polymers, proteins or particles can also be used to protect colloids against flocculation. For protein adsorption, often used for instance in food emulsions, we refer to [28]. Using particles to stabilize colloids is referred to as Ramsden-Pickering stabilization [29]. Finally, the depletion interaction will be treated in Sect. 1.2.5. 

The life time of the transient gel is determined by the strength of the depletion interaction and the colloid concentration and plays a role in many practical systems. For example in salad dressing, which is an oil-in-water emulsion, the depletion flocculation of the oil droplets induced by the addition of a polysaccharide such as xanthan leads to the formation of a particle network [112, 113], The yield stress of this network (in the sense of food science) stabilizes the... 

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