Optimisation of electrical conductance measurements for the quantification and prediction of phase separation in o/w-emulsions, containing hydroxypropylmethylcelluloses as emulsifying agents

Different hydroxypropylmethylcelluloses, Methocel E and K, and one methylcellulose, Methocel A (Colorcon, Kent), were evaluated for their emulsifying properties. Eight o/w emulsions were prepared with 20% (w/w) arachidic oil and 80% (w/w) aqueous phase containing the emulsifying agent in different concentrations. Methocel K100-LV, Methocel E50-LV and Methocel A4C were used in a 2% (w/w) concentration, while Methocel A15-LV was used in a 1, 2, 3 and 4% (w/w) concentration. The stability of the emulsions was assessed with four different techniques: visual inspection, electrical conductance, droplet size (Coulter counter) and viscosity measurements. The Methocel A15-LV 1% emulsion showed a visual instability after only 3 days, followed by the 2% emulsion (6 days) and the ESO-LV (2%) emulsion (55 days). The Methocel A15-LV 3 and 4%, the Methocel K100-LV (2%) emulsion and the A4C (2%) emulsion showed no visual instability after 90 days. For all emulsions, the difference in electrical conductance between the upper and lower part of the conductance cell, especially designed for the stability study, gradually increased with ageing. Droplet size measurements showed no major differences in droplet size as a function of time, probably due to the fact that before measurements the emulsions had to be gently shaken before sample taking. The conclusion of this study is that the electrical conductance measurements in the specially designed cells can be used to quantify and predict the phase separation in o/w-emulsions. (C) 1997 Elsevier Science B.V.