Ionic dispersion, aqueous electrolyte solutions

The micelles form the second phase that can offer dispersive (hydrophobic), polar (hydrophilic) and ionic interactions with the solutes in contrast to largely polar interactions with the aqueous electrolyte. 

The sharp double-barrel pipettes are then filled with electrolyte solution (typically aqueous salt solutions between 1 and 100 mM ionic strength), which can also contain other species (such as redox mediators or a nanoparticle dispersion). We have also successfully employed room temperature ionic liquids (RTILs) in SECCM. The electrolyte solution naturally forms a small liquid meniscus over the end of the pipette, connecting the two barrels. QRCEs are inserted into each barrel, and a conductance cell is formed between the QRCEs and across the liquid meniscus. Ag/ AgCl and Pd-H2 electrodes have been used as QRCEs. To help confine an aqueous meniscus, the outside walls of the pipette are often salinized using dimethyldichlorosilane [Si(CH3)2Cl2]. ... 

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]. 

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