Self-Assembled Aggregates Originated from the Balance of Hydrogen-Bonding, Electrostatic, and Hydrophobic Interactions

Abstract

Rich phase behavior was observed in salt-free cationic and anionic (catanionic) mixtures of a double-tailed surfactant, di(2-ethylhexyl)phosphoric acid (abbreviated as DEHPA), and tetradecyldimethylamine oxide (C(14)DMAO) in water. At a fixed C(14)DMAO concentration, phase transition from L(1) phase to L(α) phase occurs with increasing amounts of DEHPA. Moreover, in the L(α) phase, with the increase in DEHPA concentration, a gradual transition process from vesicle phase (L(αv)) to stacked lamellar phase (L(αl)) was determined by cryo- and FF-TEM observations combining with (2)H NMR measurements. The rheological data show that the viscosity increases with DEHPA amounts for L(αv) phase samples because of the increase in vesicle density. At a certain molar ratio of DEHPA to C(14)DMAO, i.e., 80:250, the samples are with the highest viscoelasticity, indicating the existence of densely packed vesicles. While for L(αl) phase samples, with increasing DEHPA amount, a decrease of bilayer curvature was induced, leading to a decrease of viscosity obviously. Compared with general catanionic surfactant mxitures, in addition to the electrostatic interaction of ion pairs, the transition of the microstructures is also ascribed to the formation of the hydrogen bonding (-N(+)-O-H···O-N-) between C(14)DMAO molecules and protonated C(14)DMAOH(+), which induces the growth of aggregates and the decrease of aggregate curvatures.

Self-Assembly and Rheological Properties of a Pseudogemini Surfactant Formed in a Salt-Free Catanionic Surfactant Mixture in Water

“…In a frequency range of 4−30 s −1 , a shear-thickening region is detected ( Figure 8C,D), indicating a shear-induced aggregate transition from the open and/or branched bilayers to closed ones, i.e., vesicles. 51 From Figure 8, it is noticed that G′, |η*|, η, and τ do not increase monotonously with increasing c C 14 -S-C 14 . Instead, they vary only slightly and even decrease a bit in some cases.…”

Investigation on the self-assembled behaviors of C18unsaturated fatty acids in arginine aqueous solution

“…Interestingly, an apparent doublet quadrupole splitting peak was observed, indicating the formation of lamellar structure. 43 For linoleic acid and linolenic acid, the water molecules bounded at the interface of curved bilayers exhibited local anisotropy, but a long-range isotropy; only a single narrow peak was observed in the spectrum.…”

“…With further addition of oleic acid, at c C 18:1 ¼ 210 mmol L À1 , the viscosity did not change more because of the formation of the lamellar phase (L al ). 43 Linoleic acid and linolenic acid exhibited very low viscosities even at higher concentrations, which reected the formation of small low-density vesicles.…”

Synthesis and physiochemical properties of novel gemini surfactants with phenyl-1,4-bis(carbamoylmethyl) spacer

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A series of novel gemini surfactants, namely phenyl-1,4-bis [(carbamoylmethyl) N,N-dimethylalkyl ammonium chloride)] (a, b and c) were synthesized systematically and characterized by FT IR, 1 H NMR, 13 C NMR and MS. Their surface and bulk properties were evaluated by surface tension, conductivity, viscosity, dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. [21][22][23][24] The most widely studied gemini surfactants are cationic alkanediyl-α,ω-bis (alkyldimethyl -ammonium) dibromide, which are referred to as CMC s C m , where m and s stand for the carbon atom number in the tail alkyl chain and in the methylene spacer, respectively. The DLS and TEM studies showed that the aggregations of the above surfactants changed from larger globule vesicles and smaller globule micelles to network aggregates and then to globule vesicles with the increase of the surfactant concentration.

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