Polymer-stabilized emulsion systems: Structural characteristics and physical stability evaluation

Abstract

In the course of investigation of the effects of polymeric emulsifier (Simulgel(R)A) on the structural characteristics and physical stability (during storage time) of semisolid o/w emulsion systems with different emulsifier concentrations, dispersed droplets of an internal oil phase (4.5-11.5 mum size) were discovered. The degree of dispersity was increased along with increasing polymeric emulsifier concentration (from 1 to 5% m/m), which was shown by microscopic analysis. Experiments were also carried out using pH, electrical conductivity, and rheological (rotational and oscillatory) measurements. Emulsion samples expressed a mild acid value acceptable for topical preparations during a 6-month period. Electrical conductivity of fresh samples ranged from 0.423 to 2.009 mS/cm and after a 6-month period this slightly increased to 0.663-2.890 mS/cm. All emulsion samples revealed plastic flow behavior in fresh state, with changes in flow pattern during storage time. Viscoelastic properties defined by the oscillatory rheometry results were in good correlation with parameters of rotational rheometry and degree of internal phase dispersity. High yield stress values (flow tests) and favorable low values of damping factor (oscillatory studies) both indicated good internal structuring and long-term stability of sample containing 3% m/m of polymeric emulsifier.