Neutral colloid

Molality Neutral colloid Neutral salt Ionic micelle Oleate anion Alkali ion... 

Polyanions complexation, charge neutralization colloidal aggregates stable turbid dispersions flocculated precipitates coherent gels... 

Addition of different kinds of charged polymers (polyelectrolytes) offers one effective way to control the stability of a colloidal solution. When charged polymers adsorb on neutral colloids, the colloids repel each other for electrostatic reasons. This behavior is called electrostatic stabilization and is responsible for the long shelf-life of certain latex paints. Polymers can also stabilize a dispersion for steric reasons when they are grafted or adsorbed to the particles. If two polymer covered particles approach it will lead to a restriction on the configurational freedom for the polymers giving rise to a repulsive force. 

Electrical stabilization of neutral colloids can occur by adsorption of charged polyelectrolytes. The complex of polyelectrolytes and colloids now become charged and we are back to the situation described in Sec. IV, where... 

Long polymer chains are soluble in low molecular mass liquid solvent. Thus, in solution, polymer chains repel one another. This is remarkable, if we consider colloidal systems in general. Namely, (neutral) colloidal particles, dispersed in a liquid tend to aggregate as a result of the van der Waals forces. Such van der Waals forces exist also between polymer chains in solution, but they are weaker and counterbalanced by entropy contributions. 

Light-yellow to yellowish-brown powder. Freely sol in water forming neutral, colloidal solns. The pH of a 5% soln... 

Figure 2.5.15 Organic polyelectrolytes (e.g., DNA) and inorganic colloids with negative surface charges are efficiently coated by cationic-neutral bolaamphiphiles. The neutralized colloid with the soft membrane surface does not precipitate and dissolves organic compounds on the surface.

Then follows a region, in which the opposite takes place. Both the conductivity and the osmotic effect decrease — the second decrease is more rapid — and from this Me Bain concludes that neutral colloidal particles have been formed. 

Lottermoser and Frotscher ask what is the origin of these large discrepancies with Me Bain s conception. The objection to Me Bain s ideas is that he works them out on the bases of the classical theory of dissociation and it is a great question whether this is permissible with the associated soap molecules and ions. Lottermoser in fact sees the explanation of the sudden fall of the conductivity in the formation of neutral colloid, after which this neutral colloid slowly makes way for ionic micelles, which again results in a rise of the conductivity. 

Thus the mobility must increase considerably to an extent dependent on the ratio of charge and radius. These considerations lead Me BaiN to attribute the fall of the conductivity to the formation of undissociated soap molecules, while Lotter-moSer thinks that neutral colloid is produced in these circumstances. This conception by Me Bain is very improbable according to Hartley, since the considerable increase of the solubility of the soap above the critical concentration is then inexplicable (see Fig. 3). Also it is not clear to what the considerable solvent power for organic compounds could be attributed. Everythii indicates that micelles are, in fact produced at the critical concentration. Such a micelle of many fatty acid anions may however be considered more or less as a polyvalent ion and this makes it probable that deviations from the classical laws of ions occur. In the first place large Debye-Huckel effects can be expected, while on the other hand, a large part of the counter ions will be bound. This latter must be found by a comparison of the conductivity and the transport numbers (Hartley ). From such an investigation it I... 

Recapitulating we can therefore say that Hartley believes that he can explain all the properties of soap solutions with one kind of micelle. This micelle as far as its structure is concerned stands more or less midway between the ionic micelle and Me Bain s neutral colloid. ... 

The suitable alternatives to alkoxide-based precursor systems for titania is the oxo-lactato-titanate of ammonium, the so-called TiBALDH or TALH, stable at neutral pH and capable to produce Ti02 nanoparticles in solution equilibrium at room temperature, and for sihca - the water glass - is the water-soluble sodium silicate that can be converted into pH neutral colloid by action of a buffer [146,147]. 

First, the fundamental forces between neutral colloidal spheres are the same as the fundamental forces between neutral polymers. Polymers and colloids are equally subject to excluded-volume forces, hydrodynamic forces, van der Waals interactions, and to the random thermal forces that drive Browiuan motion. 

What physical forces affect colloid dynamics Three forces acting on neutral colloids are readily identified, namely random thermal forces, hydrodynamic interactions, and direct interactions. The random thermal forces are created by fluctuations in the surrounding medium they cause polymers and colloids to perform Brownian motion. As shown by fluctuation-dissipation theorems, the random forces on different colloid particles are not independent they have cross-correlations. The cross-correlations are described by the hydrodynamic interaction tensors, which determine how the Brownian displacements of nearby colloidal particles are correlated. The hydrodynamic drag experienced by a moving particle, as modified by hydrodynamic interactions with other nearby particles, is also described by a hydrodynamic interaction tensor. 

Fourth, I consider solutions of hard-sphere colloids. Neutral polymers and neutral colloids interact through precisely the same forces. They have hydrodynamic interactions, and they cannot interpenetrate. They differ only in their geometry. As will be seen, Iheir dynamic behaviors are also quite similar, speaking to the possible significance of topological interactions in polymer dynamics. 

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