Novel Organized Structures in Mixtures of a Hydrophobically Modified Polymer and Two Oppositely Charged Surfactants

Abstract

In solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC) and two oppositely charged surfactants, sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium chloride (DoTAC), an organized structure of micelles has been observed by using cryogenic temperature transmission electron microscopy (cryo-TEM). On the cryoelectron micrographs the micelles appear to be thread on strings, arranged in a cell-like pattern. This organized structure is induced by the polymer when the average number of polymer hydrophobic tails per mixed micelle is about 3-5, allowing hydrophobic tails from different polymer molecules to bind to the same surfactant micelle. The organized structure was not observed either in the surfactant mixture alone or in a low-viscous solution with a low number of polymer hydrophobic tails per mixed micelle. The oppositely charged surfactant mixture was studied at a total surfactant concentration of 30 mm in the presence and in the absence of 1% w/w polymer. The number of polymer hydrophobic tails per mixed micelle was varied by decreasing the micelle concentration through induced micellar growth. The micelles grow when the mole fraction of DoTAC (X) on the SDS-rich side of the phase diagram is increased. At low X values, only micelles are found, but from X ) 0.29 upward an increasing fraction of vesicles is present. Pulsed field gradient NMR was used to measure the self-diffusion of water for determining the aggregate structure and self-diffusion of the surfactant for determining the micellar aggregation number and the concentration of free SDS molecules.

Rheological study of hydrophobically modified hydroxyethyl cellulose and phospholipid vesicles

“…As mentioned in Section 2, the contour length of HMHEC is about 760 nm. Using the persistence length of 10 nm [48], the radius of gyration is estimated to be around 50 nm [53], which is smaller than but could be comparable to the mean gap thickness between the vesicles (the lowest value is 96 nm for EPC at 15 mg/ml). It implies that at sufficiently high lipid concentrations, a single chain being stretched to directly bridge two vesicles is likely because of modest entropic penalty.…”

“…Increasing the aggregation number of micelles by adding salt or dodecyl trimethylammonium chloride (DoTAC), they observed a considerable increase in viscosity attributable to the increased concentration ratio of hydrophobes to micelles. When the added DoTAC amount was sufficient, vesicles emerged in coexistence with the micelles [48].…”

Properties of hydrophobically modified polyacrylamide with low molecular weight and interaction with surfactant in aqueous solution

“…The most studied polymers are hydrophobically modified ethyl(hydroxyethyl)-cellulose ethers (HM-EHEC) or hydroxyethyl cellulose (HM-HEC). 16,20,21,[25][26][27]41,53,54 Unmodified EHEC or HEC have slight hydrophobicity, and so the surfactant can bind to the polymer in a cooperative way above the cac. The corresponding HMP has more complicated binding behavior, which is believed to involve a two-step process.…”

Supramolecular Fluid of Associative Polymer and Viscoelastic Surfactant for Hydraulic Fracturing

“…The supramolecular structure is a well-defined complex of molecules held together by noncovalent bonds, including hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi/pi interactions, and electrostatic effects. The complex fluid structure with cationic surfactant and associative polymer has been studied by Panmai et al (1999) and Couillet et al (2005). The elongated wormlike micelles and polymer entangled and merged with each other more strongly, and the viscosity was enhanced significantly.…”