Latex particles surface charge

The source of electrostatic stabilization for latex particles is charged moieties on the surface of particles. At some pH value these groups protonate and the particles lose their surface charge. The pH at which particles have zero charge is referred to as the isoelectric point... 

The negatively charged hydrophilic headgroup of the anionic surfactants may comprise sulfate, sulfonate, sulfosuccinate or phosphate groups attached to an extended hydrophobic backbone [82]. The nature of the hydrophilic group will influence the extent of electrostatic stabilization, the behaviour of the surfactant as a fiinction of pH, the degree of hydrolysis, and the variation of latex stability with time, electrolyte and temperature conditions. The nature of the backbone hydrophobe will influence the adsorption behaviour of the surfactant onto the latex particle surface, its cmc value, the interfacial tension (which affects monomer emulsification), and the extent of steric stabilization, among other factors. 

The most widely used theory of the stability of electrostatically stabilized spherical colloids was developed by Deryaguin, Landau, Verwey, and Overbeek (DLVO), based on the Poisson-Boltzmann equation, the model of the diffuse electrical double layer (Gouy-Chapman theory), and the van der Waals attraction [60,61]. One of the key features of this theory is the effective range of the electrical potential around the particles, as shown in Figure 25.7. Charges at the latex particles surface can be either covalently bound or adsorbed, while ionic initiator end groups and ionic comonomers serve as the main sources of covalently attached permanent charges. 

A. Kampes, B. Tieke Self-Assembly of Carboxylated Latex Particles at Charged Surfaces ... 

Chemically the NR produced by the Hevea brasiliensis species is almost pure cw-l,4-polyisoprene. So far none of the manufacturers of synthetic cis-, A-polyisoprene is able to achieve more than 95% of the cis isomer in their commercial products. Jitladda and coworkers have conducted extensive studies on the molecular structures of the NR molecules found in Hevea and correlated these to the biosynthesis of this in the trees. This is intrinsically linked to the end groups of the rubber molecules involving the phospholipids and proteins that are linked to the charging mechanism at the latex particle surface and hence has a direct impact on the stability of the latex. 

The colloidal properties of latex products are of great importance from both academic and industrial points of view. Some representative charaeteristics include the particle size and particle size distribution, the particle surface charge density (or zeta potential), the particle surface area covered by one stabilizer molecule, the conformation of the hydrophilic polymer physically adsorbed or chemically couplet onto the particle surface, the type and concentration of functional groups on the particle surface, the particle morphology, the optical and rheological properties and the colloidal stability. 

Since latex dispersion application properties are related to the surface properties of the latex particles, there is a need for surface characterization of the particles at large. Historically, these types of systems have been applied as model colloids (Hearn et al, 1981) and therefore required well-characterized surfaces but as the sophistication of new coatings increase, the latex particle surfaces become more important from an industrial perspective. In addition to these applications the utilization of latex particles in pharmaceutical and biomedical applications has also contributed to the development of new surface characterization methods. The surface engineering, that is, variations in size, surface charge and surface hydrophobicity, of latex particles as colloidal carriers has been demonstrated to provide opportunities for the site-specific delivery of drugs (Ilium Davis, 1982). Surface... 

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