Aggregation of surfactants in aqueous systems

Abstract

Surfactants form micelles in aqueous solution above the critical micelle concentration (cmc); micelles are dynamic structures. Micellization is driven by the transfer of surfactant chains from water to the micelle core. There is an optimum size (aggregation number) and shape for micelles (dependent on surfactant molecular shape and packing within micelles) for which the standard free energy of micellization, Δ‎micμ‎o, is minimum. Inert electrolyte influences the degree of dissociation (α‎) of ionic micelles and hence micellar shape and aggregation number. Micellization in mixed surfactant solutions, and in mixed polymer + surfactant systems is also discussed. Micelles can dissolve (solubilize) other amphiphilic materials and nonpolar oils, which changes the cmc. If sufficient oil is solubilized, microemulsion droplets result (see Chapter 10). As the concentration of micelles in solution rises, intermicellar interactions lead to the formation of a variety of lyotropic liquid crystalline phases (mesophases).

Simulating micelle self-assembly to assess potential for viscosity build in surfactant formulations

“…However, a surfactant that produces large WLMs may display low viscosity if the micelle breakage rate is sufficiently high. In addition, past a certain threshold, viscosity might decrease due to the emergence of branching, or the formation of lamellar (or disclike) structures (Rogers et al, 2014;Aveyard, 2019). Nevertheless, the primary mechanism of viscosity build in micellar systems involves growth and entanglement of long WLMs (Aveyard, 2019).…”

“…In addition, past a certain threshold, viscosity might decrease due to the emergence of branching, or the formation of lamellar (or disclike) structures (Rogers et al, 2014;Aveyard, 2019). Nevertheless, the primary mechanism of viscosity build in micellar systems involves growth and entanglement of long WLMs (Aveyard, 2019). Given these trends, it is interesting to explore if simulating self-assembly can be used to screen candidate surfactants and formulations for potential viscosity enhancement.…”

Rhodamine 6G–Anionic Surfactant System Modified by Triton X-100 for Fluorescence Determination of Albumin

“…The effect of surfactant modifiers on organic analytical reagents is generally distinguished due to the processes of association and solubilization. 1,2 Associates of organic reagents and surfactants are valuable analytical forms in many research methods. Such associates can also act as reagents.…”

“…Properties of reagent–surfactant associates are determined by the nature and concentration of associate-forming particles, hydrophobicity, composition, and colloid-chemical properties of the formed systems. 2 Reagent–ionic surfactant associates act as analytical forms in fluorescent and spectrophotometric methods and in other methods. 3-6 Nonionic surfactants are used to modify the properties of associates due to their solubilizing properties and ability to stabilize the colloid-chemical state of the system.…”

“…9,10 Electroneutral associates, which are poorly soluble in water and capable of colloidal aggregation, sub-stoichiometric surfactant or reagent-excess associates, formed mainly due to hydrophobic interactions in the system, are also formed in the reagent–surfactant system. 2,9,10…”