Stability of the colloidal

An approximation of the correct amount of protein to be added to a gold sol to maintain stability of the colloid can be done using the following protocol (Slot and Geuze, 1984). 

Inert electrolytes, i.e., ions which are not specifically adsorbed, compress the double layer and thus reduce the stability of the colloids (Fig. 7.4). A critical coagulation concentration, Cs or ccc, can be defined (see Eqs. (4) and (5) in Table 7.3) which is independent of the concentration of the colloids (Schulze-Hardy Rule). 

In another application, the magnitude of the zeta potential is measured as a function of added counterions. The variation in zeta potential is found to be related to the stability of the colloidal suspension. The results of a gold colloidal suspension (gold solute) are reported as follows ... 

Porous inkjet papers are in general created from colloidal dispersions. The eventual random packing of the colloid particles in the coated and dried film creates an open porous structure. It is this open structure that gives photographic-quality inkjet paper its apparently dr/ quality as it comes off the printer. Both the pore structure and pore wettability control the liquid invasion of the coated layer and therefore the final destination of dyes. Dispersion and stability of the colloidal system may require dispersant chemistries specific to the particle and solution composition. In many colloidal systems particle-particle interactions lead to flocculation which in turn leads to an increase in viscosity of the system. The viscosity directly influences the coating process, through the inverse relation between viscosity and maximum coating speed. 

Fig. 6.131. The energy of interaction between two colloidal particles as a function of their distance apart, when the conditions factor stability of the colloid.

The results in Table 13.1 have been collected for colloids bearing both positive and negative surface charges. One of the earliest (1900) generalizations about the effect of added electrolyte is a result known as the Schulze-Hardy rule. This rule states that it is the valence of the ion of opposite charge to the colloid that has the principal effect on the stability of the colloid. The CCC value for a particular electrolyte is essentially determined by the valence of the counterion regardless of the nature of the ion with the same charge as the surface. The numbers listed in parentheses in Table 13.1 are the CCC values in moles per liter for counterions of the... 

With selenium sols prepared by means of hydrazine hydrate at the ordinary temperature, by pouring into a large volume of water it has been shown that the stability of the colloid depends mainly on the degree of dispersion. An optimum concentration of electrolyte is necessary for the stability of the hydrosols. In the absence of electrolytes the system is quite unstable towards freezing. 

Any of the particle sols prepared above may be used to adsorb macromolecules to create gold probes. To concentrate the suspensions, the solutions may be filtered through a small-pore filter. Centrifugation also may be done. Each protein-gold complexation should be optimized for the proper amount of protein to add to maintain stability of the colloid. This can be done according to the method described in Section 1. 

Colloids. Colloids include particles with hydrophobic, hydrophilic and intermediate forms with a size range 1 - 400 nm. Both organic (including macromolecules) and inorganic (hydrolyzed silica and metal oxides) colloids occur in the marine environment (Sigleo and Helz, 1981). Their surfaces often contain suitable sites for interactions with trace metals (adsorption, complexation). In the marine environment all particles have a negative surface charge (Neihof and Loeb, 1972 Hunter and Liss, 1982). Increase of the electrolyte concentration decreases the stability of the colloidal particles. As a result the... 

Gouy1 and Chapman,2 who were the first to predict the distribution of electrolyte ions in water around a charged flat surface, demonstrated that the ions form a diffuse layer (the electric double layer) in the liquid near the interface. The interaction between two charged surfaces, due to the overlapping of the double layers, was calculated much later by Deryaguin and Landau3 and Verwey and Overbeek.4 The stability of the colloids was successfully explained by them in terms of a balance between the double layer and van der Waals interactions (the DLVO theory).3 4... 

The stability ratio W, which constitutes a measure of the stability of the colloidal system, is defined as... 

If the grafted polymer is not adsorbed on the second plate, then the grafted polymer provides only steric interaction between the plates. This repulsive steric interaction increases the stability of the colloidal system. To calculate the steric interaction between two plates, the adsorption constant Kads in eq 11 should be taken to be zero in this case. 

The stability of a colloidal dispersion generally decreases as the electrolyte concentration increases.2 At low electrolyte concentrations, the electrostatic repulsion is responsible for the stability of the colloidal system. However, at sufficiently high electrolyte concentrations, the thickness of the double layer is significantly decreased, and the electrostatic repulsion no longer contributes to the stability of the system. 

The steric stabilization, which is imparted by polymer molecules grafted onto the colloidal particles, is extensively employed.3 Amphiphilic block copolymers are widely used as steric stabilizers. The solvent-incompatible moieties of the block copolymer provide anchors for the polymer molecules that are adsorbed onto the surface of the colloidal particles, and the solvent-compatible (buoy) moieties extend into the solvent phase. When two particles with block copolymers on their surface approach each other, a steric repulsion is generated bet ween the two particles as soon as the tips of the buoy moieties begin to contact, and this repulsion increases the stability of the colloidal system.4-6 Polymers can also induce aggregation due to either depletion 7-11 or bridging interactions.12 15... 

Addition of soluble macromolecules (polymers) in the colloidal dispersion can stabilize the colloidal particles due to the adsorption of the polymers to the particle surfaces. The soluble polymers are often called protective agents or colloids. If the protective agents are ionic and have the same charge as the particles, the electrical double-layer repulsive forces will be increased and thus the stability of the colloidal particles will be enhanced. In addition, the adsorbed polymers may help weaken the van der Waals attraction forces among particles. However, the double-layer repulsion and the van der Waals attraction cannot account for the entire stabilization of the particle dispersions. 

What the majority of these systems rely on is the stability of the colloidal dispersions involved. This in turn requires the existence of a repulsive force between the charged entities i.e., a repulsive double layer force. 

Palladium Hydrosol or Colloidal Palladium is readily prepared by the reduction of the chloride with acrolein5 or with hydrazine hydrate, in either case in the presence of an extract of Iceland moss 6 or in contact with sodium lysalbinate or protalbinate,7gum acacia,8 or with lanolin9 in a precisely similar manner to platinum,10 the function of the organic additions, which are protective colloids, being to increase the stability of the colloidal phase. 

It will be observed that even small quantities of gelatin exert a most important influence, retarding the decomposition of the peroxide very considerably, as is usual with a protective colloid. The gelatin, however, increases the stability of the colloidal metal solution, and tends to prolong its period of activity by preventing its precipitation by electrolytes, thereby enabling many reactions to be studied other than the decomposition of pure hydrogen peroxide solution. 

The thermodynamic stability of the colloidal gel state has a perfectly natural explanation in terms of the coulombic attraction theory. Just as —> 0 as Xm —> 2a,... 

Colloids are either hydrophilic (water-loving) or hydrophobic (water-hating). Hydrophilic colloids (e.g., proteins, humic substances, bacteria, viruses, as well as iron and aluminum hydrated colloids) tend to hydrate and thereby swell. This increases the viscosity of the system and favors the stability of the colloid by reducing the interparticle interactions and its tendency to settle. These colloids are stabilized more by their affinity for the solvent than by the equalizing of surface charges. Hydrophilic colloids tend to surround the hydrophobic colloids in what is known as the protective-colloid effect, which makes them both more stable. 

As has already been mentioned, the results of experiments on the stability of colloidal solutions are difficult to compare inasmuch as they were made with different concentrations of the sol, different pH, and with sols of different purity. Therefore we carried out several series of experiments with undialyzed colloidal solutions of FcjOj of various concentrations and strictly controlled pH values. The dependence of the stability of the colloidal solutions on time, the relationship of concentration of the sol and pH, the effect of electrolytes on sols of different concentration, and several other questions were studied. The results obtained are given in summary. 

Any consideration of the stability of polymer latices would be incomplete without some discussion of the stability of the colloidal polymer particles formed during the course of an emulsion polymerization. As pointed out 1 Dunn and Chong (1 70) the adsorption of the emulsifier plays a major role in determining the surface charge density of the particle and hence in determining the final particle si%. 

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