Preparation of three morphologically different states of a lamellar phase

Abstract

An aqueous L₂-phase from uncharged zwitterionic surfactants alkyldimethylaminoxide and cosur-factants in which a few percent of the zwitterionic surfactants are protonated can exist in three well-defined structurally different states:

• —a state with stacked bilayers (state I),

• —a state with polydisperse multilamellar vesicles (state II),

• —a state with monodisperse small unilamellar vesicles (state III).

State I can be prepared from a L₃-phase that is at rest and in which the bilayers are protonated with formic acid which is produced by hydrolysis methylformiate that is added to the of L₃-phase. State II can be obtained from state I by modestly shaking a sample in state I. State III is obtained if a sample in state II is sheared for about 1 h at high shear rates (∼ 4000 s⁻¹). All three states have different macroscopic properties and can be kept without change for long times (days and weeks). State I has a domain-like birefringence and is a low viscous solution. State II is a viscoelastic fluid that shows stress birefringence and state III is a viscoelastic fluid with no birefringence.