Particles , polymeric surfactant adsorption interaction

Since hydrophobic interactions appear to play a significant role in determining surfactant adsorption it is possible that these interactions may also alter the manner in which a mixture of surface-active materials might adsorb. In a very early investigation, Orr and Breitman [39] found that when mixtures of anionic and nonionic surfactants were adsorbed onto a polymeric latex particle there was a decrease in the adsorption area per molecule for the anionic surfactants. Hay et al. [40], however, observed a decease in total adsorption for sodium dodecyl sulfate and 0-n-octyltetraethylene glycol onto graphitized carbon. 

This chapter will start with a short account of the general classification and description of polymeric surfactants. This is followed by a summary on then-solutions properties. The adsorption and conformation of polymeric surfactants at the solid-liquid interface will be discussed at a fundamental level and some experimental results will be presented to illustrate the prediction of the theories. The interaction energies between particles or droplets containing adsorbed polymeric surfactants will be briefly described. The final section will give some applications of polymeric surfactants in suspensions, emulsions, and multiple emulsions. 

The attractive forces between suspension particles are considered to be exclusively London-van der Waals interactions (except where interparticle bridging by long polymeric chains occurs). The repulsive forces, as discussed in Chapter 8, comprise both electrostatic repulsion and entropic and enthalpic forces. In aqueous systems the hydrophobic dispersed phase is coated with hydrophilic surfactant or polymer. As adsorption of surfactant or polymer (or, of course, both) at the solid-liquid interface alters the negative charge on the suspension particles, the adsorbed layer may not necessarily confer a repulsive effect. Ionic surfactants may neutralize the charge of the particles and result in their flocculation. The addition of electrolyte such as aluminium chloride can further complicate interpretation of results electrolyte can alter the charge on the suspension particles by specific adsorption, and can affect the solution properties of the surfactants and polymers in the formulation. Some aspects of the application of DLVO theory to pharmaceutical suspensions and the use of computer programmes to calculate interaction curves are discussed by Schneider et al. [4]. 

When conventional surfactants are used in emulsion polymerization, difficulties are encountered which are inherent in their use. Conventional surfactants are held on the particle surface by physical forces thus adsorption/des-orption equilibria always exist, which may not be desirable. They can interfere with adhesion to a substrate and may be leached out upon contact with water. Surfactant migration affects film formation and their lateral motion during particle-particle interactions can cause destabilization of the colloidal dispersion. 

The latter values could also be used to calculate the molecular dimensions (radius of gyration) and the polymer-solvent interaction parameter x was also determined. The polystyrene latex used for the adsorption measurements was a model system prepared using surfactant-free polymerization and the particles were fairly monodisperse. Hence, the specific surface area of the particles could be estimated from simple geometry using electron microscopy. 

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