Emulsions charge-stabilised

Charge-Stabilised Emulsions (e.g., Using Ionic Surfactants)... 

When dispersed in water the flakes become hydrated, the positively charged comers focus oti the negatively charged flat sides of other particles and a hydrogel is formed. Because of this stmcture the liquid is viscous and thixotropic. Aluminium magnesium silicate therefore is often used to stabilise emulsions and suspensions. 

Nonionic surfactants cannot increase the surface charge and may actually reduce it. They may also screen the droplets charge from one another. These surfactants stabilise emulsions by a steric mechanism. Nonionic surfactants always have large hydrophilic groups which extend away from the droplet surface a significant distance and impose a barrier to encounter. 

As in the case of rosin sizing, the first step is to retain the emulsified size particle in the wet web. The mechanism of retention is probably by heterocoagulation of the cationic size particles to the negatively charged fibre surface. The charge characteristics of the stabilising polymer become important as demonstrated by the effect of pH on the retention of AKD emulsion particles stabilised with a tertiary cationic starch (Figure 7.17). 

Electrical double layer repulsions (see page 212) Interparticle repulsion due to the overlap of similarly charged electric double layers is an important stabilising mechanism in O/W emulsions. 

Styrene-butadiene latices were prepared by emulsion-free polymerisation in the presence of N,N-diethylaminoethyl methacrylate to supply a positive charge and their colloidal behaviour and interaction with anionic pulp fibres investigated. It was found that the latices were positively charged and stabilised by electrostatic repulsion and deposited readily on anionic fibres suspended in water, forming a monolayer on the fibre surface. Dewatering and drying resulted in coalescence of the particles and fibres covered with a polymeric film, which improves the bonding between the fibres. 9 refs. CANADA... 

The polymerisation and the properties of the latexes depended sensitively on the emulsifier and on the charge of the initiator. There was no visible correlation between the properties of the final latexes and the properties of the emulsifiers such as surface activity, solubilisation capacity, or the ability to stabilise the initial monomer emulsion. When a cationic (2,2 -dimethyl-2,2 -azo-N-benzylpropionamidine hydrochloride, VA-552 from Wako Chemicals) initiator was employed, all emulsifiers lead to stable monodisperse latexes, except for polysoaps with low hydrophobe content. The polymerisable, as well as the polymeric emulsifiers, yielded latex solutions with very high surface tensions, different from the use of the standard surfactant. In contrast, the use of an anionic initiator (potassium persulphate) can pose difficulties. The... 

We start with the simpler case of emulsions and/or microemulsions, stabilised with nonionic surfactant. This means that there are no charge effects present and in the extremely simplest situation (all long range forces are neglected, including van der Waals) we may account only for the surface bending. For a small deformation ... 

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