Microemulsions for dermal drug delivery studied by dynamic light scattering: effect of interparticle interactions in oil-in-water microemulsions.

Dynamic light scattering (DLS) was used to study the droplet size and the droplet interaction of o/w microemulsions (MEs) consisting of oils, a blend of a high and a low hydrophilic-lipophilic balance (HLB) surfactant, and a hydrophilic phase (propylene glycol/water). Like many MEs, these systems could not be diluted to infinite dilution without phase separation. Consequently, to allow a meaningful calculation of droplet diameter from data obtained from DLS, it is necessary to correct scattering measurements in high concentration regions for the nonideality arising from interparticle interaction. Scattering data were corrected for interparticle interaction using a suitable interaction model proposed for our systems. From the total interparticle interaction energy, coagulation time was calculated. The ratio between rapid and slow coagulation was of the order of 10(100), which is consistent with the observed stability of the MEs studied.