Wormlike micelles (WLMs) are aggregates assembled from amphiphilic molecules and form long, thread-like structures under high salt conditions. The robust long-chain characteristic of WLMs, and their ability to entangle, yields unique viscoelastic properties associated with widespread application. The actual performance of micellar products depends highly on the size and shape of surfactant aggregates, which can be altered through adjustment of the balance between solvent incompatibility with the tail groups and solvent electrostatic interactions with the head groups. Commonly used strategies to adjust such balance are to tune concentrations of salt as well as other additives to adjust the structure of the aggregates<br/>A mixed surfactant system composed of a common anionic surfactant, sodium laureth sulfate-1 (SLES1), modified by a zwiterionic surfactant, cocamidopropyl betaine (CAPB) is studied. Small angle neutron scattering (SANS) was employed in the investigation of the structure of micelles in the presence of both inorganic salt and co-solvent. The scattering contribution of samples were fitted by hybrid unified function which allows the determination of local cylindrical structure and larger scale structure info including micellar contour length and extend of branching. SANS also allows understanding of WLMs behaviors from thermodynamic prospective. Free energy, entropy and enthalpy of scission (forming two end-caps) were obtained based on slight modification of Cates and Candau’s theory. The relative dependence of contour length/scission energy on salt concentration in the presence and absence of co-solvent is studied. The self-assembled structure can be tuned by adjusting solvent polarity without affecting the relative tunability of the WLM structure through counter ion concentration. Further interpretation on entropy and enthalpy change will also be presented.

Structure and thermodynamics of worm-like micelles with addition of salt and co-solvent

255th National Meeting (2018)

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