Surfactant stabilised colloidal cholesterol

Abstract

Cholesterol colloids stabilised by Tween 20 (Colloid I), SDS-Et₄ NBr (Colloid II), and CTAB-Nac (Colloid III) were prepared. Moving boundary electrophoresis established Colloid III to be positively charged with a zeta potential of 12.2 mV. Addition of 5 mmol dm⁻³ Na₂SO₄ and 0.1 mmol dm⁻³ bilirubin dye (Na-salt) decreased the zeta potential to 9.7 mV and 9.5 mV, respectively, by screening the surface charge of the colloidal particles. Higher concentrations of Na₂SO₄ and bilirubin (Na-salt) made making electrophoretic measurements difficult, and such a situation was also faced in the case of Colloid II even without external addition of an electrolyte. Addition of several electrolytes revealed that Colloids II and II were coagulated by the neutralisation of their positive charge, but Colloid I was destabilised by salting-out effect. Measured intrinsic viscosity values and electron microscopic measurements supported overall spherical shape of the colloid particles. Colloid II exibited structural viscosity; higher concentration of NaSO₄ decreased the viscosities of Colloid II and II by electroviscous effect which helped indirect determination of the electrokinetic potential (23.7 mV) of Colloid II.