A New Reverse Wormlike Micellar System:Mixtures of Bile Salt and Lecithin in Organic Liquids

摘要

We report a new route for forming reverse wormlike micelles (i.e.,long,flexible micellar chains)in nonpolar organic liquids such as cyclohexane and n-decane.This route involves the addition of a bile salt (e.g.,sodium deoxycholate)in trace amounts to solutions of the phospholipid lecithin.Previous recipes for reverse wormlike micelles have usually required the addition of water to induce reverse micellar growth;here,we show that bile salts,due to their unique "facially amphiphilic"structure,can play a role analogous to that of water and promote the longitudinal aggregation of lecithin molecules into reverse micellar chains.The formation of transient entangled networks of these reverse micelles transforms low-viscosity lecithin organosols into strongly viscoelastic fluids.The zero-shear viscosity increases by more than 5 orders of magnitude,and it is the molar ratio of bile salt to lecithin that controls the viscosity enhancement.The growth of reverse wormlike micelles is also confirmed by small-angle neutron scattering (SANS)experiments on these fluids.