Surfactants settling Sedimentation

To determine the best solvent and surfactant concentration, a slurry mixture should be made up prior to packing, and dispersed by sonic vibration. The rate of sedimentation should be carefully checked over the anticipated time of packing to ensure that the solvent is sufficiently viscous and confirm that no significant settling takes place. When an appropriate solvent mixture is identified, the slurry should be prepared using l-3%w/v mixture of the packing in the solvent and should then be well shaken and examined under a microscope. 

Cellulose derivatives, especially methylcellulose and hypromellose, usually cause a strong foam at preparation because they also possess surfactant activity. For the formulation of settling suspensions they are often unsuitable as they create a sediment that is difficult to disperse. They are used in suspensions and emulsions for oral use (see Sects. 5.4.6 and 5.4.7) at concentrations of 0.25-2.5 %. In... 

At the end of the emulsion polymerisation, polymer particles will exist in the dispersed water phase with surfactant molecules adsorbed on the particle surface. It is usually considered that it is the hydrophobic portion of the surfactant that is adsorbed onto the surface while the hydrophilic portion goes into the water phase. The role of the surfactant is now to keep the system stable by preventing coalescence of the polymer particles in the dispersion. If particle coalescence is not prevented the settling of the coagulated particles can take place, giving a non-redispersible sediment. 

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