Electrosteric force

In polar media such as water, often polyelectrolytes are used. Since polyelectrolytes are charged, we have a steric and an electrostatic effect. For this reason, the effective interaction is sometimes called electrosteric force. The electrosteric force has an important advantage over simple electrostatic repulsion it is to a large degree independent of the concentration of added salt. While electrostatically stabilized dispersion often coagulates when salt is added, electrosterically stabilized dispersions are robust and remain stable. 

Surface force between various polyelectrolyte brushes has been measured [1355, 1379,1381]. Not only polymer brushes but also dense layers of physisorbed homopolymers show the general features outlined above [1372, 1380, 1382-1384]. For spherical geometries, that is, if the particle s core diameter is of the same length scale as the brush thickness, expressions for the electrosteric force are reported in Refs [1381, 1385]. 

Recognition and description of new interparticle interaction forces such as those owing to magnetic dipoles, steric and electrosteric repulsion,... 

Since the beginning of colloids science, however it is also known that the agglomeration of colloids and dispersed particles can be prevented or controlled by stabilization [8]. The attractive interactions between the colloidal particles, caused by van-der-Waals forces, need to be compensated by repulsive interactions. The latter can be based either on electrostatic repulsion due to same-sign surface charges (electrostatic stabilization), or on repulsion via a polymer shell formed through adsorption of polymers to the particle surface (steric stabilization, in presence of polyelectrolytes termed electrosteric stabilization due to additional charged-induced repulsion) [9, 10]. The stabilization by control of the interaction forces between colloidal particles has been in the focus of extensive research efforts. Already... 

The repulsive forces between the polymer particles are electrostatic, steric, or electrosteric in nature, and can be controlled deliberately by modifying the polymerization recipe. The attractive forces are the general van der Waals forces caused by dipole and induced-dipole interactions. 

In effect, we have mainly covered attractive interactions introduced when adding polymer to a system. This is because our interest here was mainly focused on retention aids which function by enhancing the attractive interactions in the papermaking system. Polymeric systems tuned to increase the repulsive force between surfaces by way of steric interactions (caused by chain overlap and loss of conformational entropy on compression), electrosteric interactions (between charged polymer brushes), and/or electrostatic repulsions (due to charge over-compensation), are equally important in practical applications. However, repulsive polymeric forces should not by any means be viewed as purely... 

To conclude, the stability of emulsions depends on droplet size, the presence of electrostatic, and/or steric, and/or electrosteric repulsion forces, the viscosity of both phases and the temperature. In addition, the kind and concentration of all stabilizers electrolytes and additives play a major role as well. 

PEG-based coatings, an electrosteric stabilization was achieved by steric forces in combination with electrostatic repulsion. 

States (a) to (c) in Figure 7.33 correspond to a suspension that is stable in the colloid sense. The stability is obtained as a result of net repulsion due to the presence of extended double layers (i.e. at low electrolyte concentration), the result of steric repulsion produced adsorption of nonionic surfactants or polymers, or the result of a combination of double layer and steric repulsion (electrosteric). State (a) represents a suspension with small particle size (submicron) whereby the Brownian diffusion overcomes the gravity force, producing a uniform distribution of the particles in the suspension, i.e. 

Ramakrishnan S., McDonald C.J., Carbeck J.D., Prudhomme R.K. Latex composite membranes Structure and properties of the discriminating layer. J. Mem. Sci. 2004 231 57-70 Romero-Cano M.S., Martin-Rodriguez A., Nieves F.J.D.L. Electrosteric stabilization of polymer colloids with different functionality. Langmuir 2001 17(11) 3505-3511 Rau D.C., Parsegian V.A. Direct Measurement of the intermolecular forces between counterion-condensed DNA double helices— Evidence for long-range attractive hydration forces. Biophys. J. 1992 61(1) 246-259... 

In the electrostatic and electrosteric mechanisms, the repulsive force required to overcome the attractive van der Waals forces is developed through the formation of the so-caUed electric double layer around particles. As previously mentioned, the buildup of this double layer starts with the generation of electric charges on the surface of particles. 

Electrostatic force depends on two parameters, Nemst potential and Zeta potential. Nemst potential has little effect on stabilization and is not practically assessable. Zeta potential is the potential difference between the electroneutral region and actual nanoparticle surface. The condition for stabiUly of nanoparticles is that the electrostatic repulsive forces should be higher than the attractive van der Waals forces. Hence, a higher value of zeta potential will result in a more colloidal stabihty of nanoparticles [65]. The different strategies to increase the stability of nanoparticles for biomedical apphcations are as follows. The first is electrostatic stabilization, in which a electric double layer around nanoparticles is formed. The second is steric stabilization in which a steric stabilizer is chemically attached or adsorbed on the nanoparticle surface. In the third approach, both the above methods are combined. Electrosteric stabilization has many advantages, such as redispersibility of nanoparticles, ability to support high concentration of nanoparticle suspensions, and electrolytic insensitivity [65-68]. 

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