Rheological Properties of Viscoelastic Solutions in a Cationic Surfactant–Organic Salts–Water System

Abstract

Viscoelastic solutions formed in the mixed aqueous solutions of 3tetradecyloxy-2-hydroxypropyltrimethylammonium bromide (R 14 HTAB) and aromatic salts such as sodium salicylate (NaSal), sodium 1-hydroxynaphthalene-2-carboxylate (1SHNC), and sodium 2-hydroxynaphthalene-3-carboxylate (2SHNC) were systematically studied by steady and dynamic shear rheology in terms of concentration and temperature. In the absence of a salt, R 14 HTAB only produced spherical or short cylindrical micelles within a range of concentrations of 100−400 mmol kg −1 . The addition of aromatic salts induced one-dimensional growth of micelles generating wormlike micelles. Zero-shear viscosity of the solutions shows viscosity maxima behavior in the examined range of salt concentration, where the strongest and the most stable network structures were formed. The changes in the viscoelastic behavior are a result of variation of the structural relaxation time, indicating that the flow behavior is primarily controlled by micellar kinetics. The microstructure of wormlike micelles and the reason for the variation in the microstructure with an increase in the additive concentration has been analyzed by infrared and 1 H NMR spectra measurements. The zero-shear viscosity reduces exponentially with increasing temperature.

Effect of Additives on Surfactant Micelle Shape Transformation: Rheology and Molecular Dynamics Studies

“…As shown in Figure 6, only a broad peak was observed at 3448 cm −1 in the 100 mmol L −1 R 14 HTAB solution in CDCl 3 (black line), which was lower than the common values of 3580−3650 cm −1 of the free hydroxyl group. 40,53 This result should be indicative of the hydroxyl group in the associated state due to the IR peak corresponding to the connection state of hydroxyl groups in the 3200−3400 cm −1 range. The latter implies the existence of intermolecular hydrogen bonding among the R 14 HTAB molecules, which had also been confirmed from the measurements of the crystal structures in previous reports.…”

“…The dispersed rod-like micelles existed at the concentration value of 25 mmol L –1 at which the shear thinning phenomenon appeared. After the maximum viscosity, the reduction in viscosity with further addition of salts was usually ascribed to branching of the wormlike micellar induced by an increase in the end-cap energy, E c , − or shortening of the mean micelle size. − In general, in cationic surfactant/salt mixture solutions, the micellar branching could take place more easily when the electrostatic interactions were adequately screened because the branching point of micelles represented a delicate balance in the electrostatic property of the solution. The formation of a 3-fold micellar junction was greatly more favorable compared to the end-cap of a micelle .…”

Coarse-Grained Molecular Dynamics Simulations of the Breakage and Recombination Behaviors of Surfactant Micelles

“…Because the stretching process of individual micelles is nearly identical, i.e., the accumulated strains, εṫ, are proportional to the micelle stretching distances, Δx, we can regard micelle behavior as a linear Hookean elastic spring. Then, the extension energy, E extension , and the accumulated strains, εṫ, can be expressed as A•εṫ + B•(εṫ) 2 , where A is a constant for each micelle's initial length. For the above four rodlike micelles, the value of A is 81.1, 167.4, 173.5, and 199.0, respectively.…”

“…Gemini surfactants can self-assemble into a wide variety of micellar morphologies because of their hydrophobic tail and hydrophilic head groups. − Various micellar structures (e.g., spherical; rodlike; lamellar; vesicular; loop and branch; and long, flexible wormlike) can exhibit rich rheological properties. − These various rheological properties are beneficial for their use in numerous applications, such as hydrofracking fluids in the oil industry, turbulent drag-reducing agents, thickening agents in consumer products, drug carriers in targeted delivery, and templates to create functional nanofluids. − However, threadlike shear-induced structure (SIS) formation and shear banding can be observed in surfactant solutions because of the merging and reversible breaking motions of many individual, wormlike micelles. − The network of wormlike surfactant micelles is beneficial for turbulent drag reduction because of their ability to absorb and release stress from turbulent kinetic energy and change the turbulent spatial structure. , Therefore, understanding the mechanism of the breakage and recombination behaviors of surfactant micelles is essential for their applications.…”

Switchable Surfactant-Based CO2-in-Water Foam Stabilized by Wormlike Micelle

“…Unlike traditional cationic, anionic, nonionic, and zwitterionic surfactants such as 3-tetradecyloxy-2-hydroxypropyltrimethylammonium bromide (R 14 HTAB), sodium dodecyl benzenesulfonate (SDBS), , sodium dodecyl sulfate (SDS), ,− α-olefin sulfonate (AOS), nonionic surfactant C 12–14 (EO) 22 , and zwitterionic amidopropylcarbobetaines (R-ONHC 3 H 6 N­(CH 3 ) 2 CH 2 CO 2 ), the switchable surfactant which can be reversibly switched “on” and “off” via external stimuli has attracted much attention in recent years. Using the appropriate trigger such as UV light, pH, temperature, , redox reactions, and CO 2 , − switchable surfactants can undergo reversible conversions.…”