Viscoelasticity Enhancement of Surfactant Solutions Depends on Molecular Conformation: Influence of Surfactant Headgroup Structure and Its Counterion

Abstract

During the anisotropic growth from globular to wormlike micelles, the basic interactions among distinct parts of the surfactant monomer, its counterion, and additives are fundamental to tune molecular self-assembly. We investigate the addition of sodium salicylate (NaSal) to hexadecyltrimethylammonium chloride and bromide (CTAC and CTAB), 1-hexadecylpyridinium chloride and bromide (CPyCl and CPyBr), and benzyldimethylhexadecylammonium chloride (BDMC), which have the same hydrophobic tail. Their potential to enhance viscoelasticity by anisotropic micellar growth upon salt addition was compared in terms of (i) the influence of the headgroup structure, and (ii) the influence of surfactant counterion type. Employing proton nuclear magnetic resonance ((1)H NMR), we focused on the molecular conformation of surfactant monomers in the core and polar shell regions of the micelles and their interactions with increasing concentration of NaSal. The viscoelastic response was investigated by rotational and oscillatory rheology. We show that micellar growth rates can be tuned by varying the flexibility and size of the surfactant headgroup as well as the dissociation degree of the surfactant counterion, which directly influences the strength of headgroup-counterion pairing. As a consequence, the morphological transitions depend directly on charge neutralization by electrostatic screening. For example, the amount of salt necessary to start the rodlike-to-wormlike micelle growth depends directly on the number of dissociated counterions in the polar shell.

Nonpolar Interface Composition in Cetyltrimethylammonium Bromide Reverse Micellar Environments to Control Size and Induce Anisotropy on Gold Nanoparticles

“…Through 1 H NMR experiments, downfield shifts were attributed to displacement of protons to more polar environments, e. g., from the micellar core to interfacial water surroundings at the micellar interface, whereas upfield shifts indicate a variation of the proton environment to a non‐polar region or better electrostatic screening . Figure A shows the 1 H NMR spectra of n‐ hexane/1‐butanol/CTAB system.…”

“…[42] Through 1 H NMR experiments, downfield shifts were attributed to displacement of protons to more polar environments, e. g., from the micellar core to interfacial water surroundings at the micellar interface, whereas upfield shifts indicate a variation of the proton environment to a non-polar region or better electrostatic screening. [43][44][45] Figure 2A shows the 1 H NMR spectra of n-hexane/1-butanol/CTAB system. H α and H β signals shift upfield with increasing W 0 suggest that H α and H β CTAB protons are in more hydrophobic and less polar environment deep in the interface layer of the micelle.…”

Simulation of Multiscale Hydrophobic Lipid Dynamics via Efficient Integral Equation Methods

“…By modification of the interfacial labels, HADF can account for charged lipids and study their impact on elastic properties of bilayer [20]. Since we have immersed the particles in a zero-Reynolds flow, it is possible to study the rheological properties of micelle networks in large particle simulations [50]. Finally, we also aim to investigate the continuum limit of our hybrid model and make comparison with functionalized We show that pairwise potentials do not closely approximate the HADF.…”

Ascorbyl‐6‐O‐oleate: A Bioconjugate Antioxidant Lipid

“…At “high” concentrations, the nanostructures take the form of an entangled network. This gives rise to a viscoelastic behaviour that is reminiscent of that of flexible polymer solutions . VES systems can also be used to produce “smart” materials.…”

“…This gives rise to a viscoelastic behaviour that is reminiscent of that of flexible polymer solutions. [15,16] VES systems can also be used to produce "smart" materials. Their properties can be controlled reversibly in response to an external stimulus.…”