Shear-Induced Structural Transition and Recovery in the Salt-Free Catanionic Surfactant Systems Containing Deoxycholic Acid

Abstract

Shear-induced structural transition and recovery were studied by freeze-fracture transmission electron microscopy, cryogenic transmission electron microscopy (cryo-TEM), rheological measurements, and the variation of birefringent textures in the system of tetradecyltrimethylammonium hydroxide (TTAOH)/lauric acid (LA)/deoxycholic acid (DeCA)/H(2)O as a function of the molar fraction of DeCA [x = n(DeCA)/(n(DeCA) + n(LA))]. At x = 0.3, giant vesicles and planar lamellar structures were formed before exerting shearing. Shear thickening and large hysteresis loop are observed under shearing, indicating the occurrence of structural transition. Multilamellar and close-packed vesicles were determined by cryo-TEM observations. Exerting further shearing, the elastic properties of the sample were increased due to the strip off of the outer shell of the vesicles and formation of small vesicles. After shearing was stopped, the sample can slowly relax back to the original state. At x = 0.25, lamellar structures, giant vesicles, and small unilamellar vesicles were observed. Cryo-TEM observations show that the multilamellar vesicles can be formed after exerting shearing, and the sample cannot spontaneously recover to the original state. At x = 0.2, vesicles are dominant in the solution, and the aggregates structures are almost the same before and after shearing. Shearing can increase the elastic properties of the sample, which is ascribed to the strip off of the outer shells of the multilamellar vesicles, forming much smaller vesicles in the solution.

Self-assembled structures of amphiphiles regulated via implanting external stimuli

“…Shear ow has a strong inuence on complex uids, especially the self-assembled structures of amphiphilic molecules in solutions. Because the introduction of mechanical force can alter the microstructures of aggregates, 73 the effect of shear force on aggregation behavior of amphiphiles has attracted growing interest over last decades both in theoretical and experimental viewpoints. Shear forces can inuence many types of aggregates in solutions, e.g., the microstructure transition among wormlike micelles, 74 sponge phase, 75 hexagonal liquid crystalline phase, 76 and lamellar structures (planar lamellar phase and vesicles).…”

“…Recently, Hao and coworkers utilized FF-TEM, cryo-TEM, and rheological measurements to investigate the shear-induced structure transition and recovery in dilute solutions of tetradecyltrimethylammonium hydroxide (TTAOH)/lauric acid (LA)/deoxycholic acid (DeCA)/ H 2 O system with the mass concentration of total surfactants being about 4.7-4.9%. 73 The molar concentration of TTAOH was equal to that of the mixed acids (LA and DeCA). When x(x ¼ nDeCA/(nDeCA + nLA)) was within 0.3-0.2, the structure transition from planar lamella to MLVs induced by shear was observed.…”

“…Fig.10The variation of shear viscosity with time at different shear rates for sample of x ¼ 0.25 at 100 mM TTAOH/(DeCA + LA) (a); Cryo-TEM images before (b) and after (c) shearing at 20 s À1 for 5000 s 73. Reprinted with permission from ref 73. (copyright (2011) American Chemical Society).…”

Lamellar-to-MLV transformation in SDS/octanol/brine examined by microfluidic-SANS and polarised microscopy

“…5,19 Experimentally, the formation of MLVs has been described by the emergence of intermediate multilamellar cylinder (MLC) phase [20][21][22] in continuous shear flow or a direct emergence of MLVs with oscillatory flows. 4 Numerous experimental reports have considered the effect of shear field, stress and rate, on various model systems (nonionic, 4,21,23,24 cationic 25,26 and anionic 27,28 ), the effect of added co-surfactants 3,29 and salt, 30,31 and the effect of oscillatory shear flows. 4,28,32 Predominant analytical techniques include rheology, 33,34 scattering, 21,22,34,35 optical microscopy 35,36 and 2 H NMR.…”

Phase Behavior, Rheological Property, and Transmutation of Vesicles in Fluorocarbon and Hydrocarbon Surfactant Mixtures

“…To date, the cationic surfactant used in salt-free catanionic surfactant mixtures is typically alkyltrimethylammonium hydroxide and the anionic surfactants are fatty acids with total carbon number ranging from 12 to 18. Recent studies have expanded to novel salt-free catanionic surfactant mixtures containing new and interesting anionic surfactants. − Although simple salt-free catanionic surfactant mixtures containing only one cationic surfactant and one anionic one have been extensively studied during the past decade, investigation of salt-free catanionic surfactant mixtures containing mixed cationic and/or anionic surfactants with different molecular structures is quite rare. In this work we present a detailed study of a salt-free catanionic surfactant mixture where tetradecyltrimethylammonium hydroxide (TTAOH) is selected as the cationic surfactant and two acids with different molecular structures and properties are selected as anionic surfactants (Scheme ).…”