also providing a charged interface for the polyelectrolyte to adsorb on. Molecular Weight Effects The stability of the emulsion can depend on the molecular weight of the accompanying polyelectrolyte. Polyelectrolytes of a high molecular weight are the most effective at stabilization. This is because they form a substantial steric barrier between oil and water, inhibiting aggregation. However, if the polyelectrolyte is too heavy it will not dissolve in the solution. Instead it will form gel lumps and fail to stabilize the emulsion. pH Effects The effect of pH on the stability of polyelectrolytes is based upon the functional group on the polymer backbone that is bearing the charge. A protonated amine, for instance, will be much more stable at a lower pH while a sulfonate group will be more stable at a higher pH. Solvent Effects Polyelectrolytes will be much more soluble in polar solvents due to the charge on the polymer backbone and will spread out more. In nonpolar solvents, polyelectrolytes will coil becoming more densely packed and, if the backbone is nonpolar, will put the charge on the inside of the packed structure. Ionic Strength Ionic strength plays a crucial role in stability. In water-in-oil emulsions, as well as many others, the dielectric constant of the solvent is so low that the electrostatic forces between particles are not strong enough to have an effect on emulsion stability. Thus, emulsion stability depends greatly on the polyelectrolyte film thickness. The polyelectrolyte film thickness is dependent upon its ionic strength. charged species on polyelectrolyte chains repel each other, causing the chains to stretch out. As the salt concentration increases, ionic strength increases, and the ions will shield the charges on the polymer chain allowing the polymer chain to form a dense random coil. Theory Electrostatic stabilization Electrostatic repulsive forces dominate in polyelectrolyte stabilized emulsions., Although there are steric interactions, they are negligible in comparison. As the concentration of polyelectrolyte increases, repulsive forces increase. When there are more polyelectrolyte molecules, the distance between individual particles decreases. As the distance decreases, the exponential term becomes greater. Consequently, the repulsion energy also increases. The general equation for repulsion energy assuming spherical particles (eq. 1): where = particle radius, = bulk concentration of ions. = Boltzmann constant, = reduced surface potential. = the surface to surface distance of the spherical particles. = the thermodynamic temperature = the Debye length. In addition, pH and ionic strength