Surface charge origin

The electrostatic stabilization theory was developed for dilute colloidal systems and involves attractive van dcr Waals interactions and repulsive double layer interactions between two particles. They may lead to a potential barrier, an overall repulsion and/or to a minimum similar to that generated by steric stabilization. Johnson and Morrison [1] suggest that the stability in non-aqueous dispersions when the stabilizers are surfactant molecules, which arc relatively small, is due to scmi-stcric stabilization, hence to a smaller ran dcr Waals attraction between two particles caused by the adsorbed shell of surfactant molecules. The fact that such systems are quite stable suggests, however, that some repulsion is also prescni. In fact, it was demonstrated on the basis of electrophoretic measurements that a surface charge originates on solid particles suspended in aprotic liquids even in the absence of traces of... 

However, in apolar media, most surfaces do not assume a surface charge (i.e /<) 0), so that they are not stabilized by electrical double-layer interaction. Only surfaces for which the surface charge originates from strong acid or base groups acquire charge in an apolar solvent. 

This diffuse double-layer approach can be applied to describe the EDL of particles, if charges on particle surface are only permanent structural surface charges originating from isomorphic substitutions of ions in a clay crystal lattice (e.g., montmorillonite, which is a typical example of infinite flat plates with a constant charge density [19]) or they form by the adsorption of potential determining ions (e.g., Ag+ ions on a Agl surface is an example of the case of charged particles with constant potential [1,33,38]) and the diffuse swarm of indifferent electrolyte ions compensates surface charges. 

For typical aqueous colloidal dispersions, the particles may carry some charges most likely due to the preferential (or differential) dissolution of particle surface ions, direct ionization of particle surface groups, substitution of particle surface ions, specific adsorption of ions, and particle surface charges originating from specific crystal structures. 

FIG. 10 Nomalized unbalanced surface charge in a cylindrical pore with R = 5din the presence of an external potential The results, from left to right, are for original surface charge densities of —0.001, —0.005, —0.01, —0.02, —0.04, —0.05, —0.07123 C/m respectively. The x-intercepts are values of the corresponding equilibrium Donnan potentials. 

In this case, three particles are shown, a 40 u, 20 p and a 10 p particle. The most important step is sample preparation on the microscope slide, since only a pinch of materied is used, one must be sure that the sample is uniform and representative of the material. Also, since most materials tend to agglomerate due to accumulated surface charge in a dry state, one adds a few drops of alcohol and works it with a spatula, spreading it out into a thin layer which dries. Too much working breaks down the original peirticles. 

In sections 1.7- 1.9 we have examined effects of surface charging in semiconductor adsorbent on electrophysical characteristics of the adsorbent. Although we did not go into details with respect to the crystalline origin of adsorbent, the consideration of effect of adsorption on electric conductivity of surface-adjacent layer led to conclusion that we considered monocrystalline samples. 

The origin of the electrochemical double layer arises from the requirements of charge neutrality in which the surface charge on the cell surface must be balanced against the opposite charge in the water (or any other fluid in a more general case). 

Specifically sorbable species that coagulate colloids at low concentrations may restabilize these dispersions at higher concentrations. When the destabilization agent and the colloid are of opposite charge, this restabilization is accompanied by a reversal of the charge of the colloidal particles. Purely coulombic attraction would not permit an attraction of counter ions in excess of the original surface charge of the colloid. 

The content of vaccine within the small liposomes is estimated as in the section Estimation of Vaccine Entrapment in Dehydration-Rehydration Vesicles Liposomes for both microfluidized and sucrose liposomes and expressed as percentage of DNA and/or protein in the mixture subjected to freeze drying as in the section Preparation of Vaccine-Containing Small Liposomes by the Sucrose Method in the case of sucrose small liposomes or in the original DRV preparation (obtained in the section Estimation of Vaccine Entrapment in DRV Liposomes ) for microfluidized liposomes. Vesicle size measurements are carried out by PCS as described elsewhere (6,8,17). Liposomes can also be subjected to microelectrophoresis in a Zetasizer to determine their zeta potential. This is often required to determine the net surface charge of DNA-containing cationic liposomes. 

Oxide surfaces are high-energy surfaces that interact with water molecules becoming covered by a carpet of OH groups. The latter, in contact with aqueous solutions, behave as weak acids or weak bases, giving rise to dissociation that is the main origin of surface charging ... 

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