In Situ Nanostructural Analysis of Concentrated Wormlike Micellar Fluids Comprising Sodium Laureth Sulfate and Cocamidopropyl Betaine Using Small-Angle Neutron Scattering

Abstract

Concentrated wormlike micellar fluids form the basis for a vast array of formulated products, from liquid soaps and shampoos to drag reduction and drilling fluids. Typically, these systems are analyzed using bulk rheological measurements to determine their flow properties and cryo-microscopy to detect their nanostructure. Smallangle neutron scattering provides an opportunity to directly and nonperturbatively analyze nanostructure in situ but is complicated for concentrated systems by correlations from interparticle volume exclusion. Here, we use small-angle and ultra-small-angle neutron scattering to probe directly for the first time the nanostructure of concentrated wormlike micellar fluids composed of the widely used surfactant pair sodium laureth sulfate and cocamidopropyl betaine in aqueous electrolytes. Obtained data are analyzed using different approaches to determine scattering contributions from the wormlike particles themselves and interactions between them. It is found that approximating worms as locally rigid cylinders offers some insight into their aggregation dimensions at short length scales, and both volume exclusion and screened Coulombic interaction potentials describe interactions reasonably well. Using the semi-empirical polymer reference interaction site model (PRISM) gives excellent agreement with observed scattering, and physical insight obtained using this approach is discussed in detail. A drawback of this method is the significant complexity in coding the model in order to fit data, so to facilitate this for future researchers, we provide with this paper a fully operational, open-source code to utilize this model.

Shear-induced nano structural changes in micelles formed by sugar-based surfactants with varied anomeric configuration

“…The combination of the PRISM model with the flexible cylinder form factor thus determines the scattering for WLM with intra-and intermicellar excluded volume effects [26]. This model has successfully been used to analyse SANS data from WLM in the semi-dilute regime [27,28]. It should be noted that the PRISM model was validated using closed-form Monte Carlo simulations of interacting WLM.…”

“…The MATLAB code used for modelling the scattering from WLM in the semi-dilute regime is presented in the Supplementary information. This code is a re-work of the model previously published by Williams et al that expands the applicability of this model to WLM of arbitrary contour length and flexibility [28].…”

“…Also, the parametrisation of the model gives a strong correlation between r eff and r. As such, they cannot simultaneously be determined through the analysis of the scattering data. Therefore, the parameter r was fixed to 1 and held constant during fitting, and r eff was fitted, as this approach has previously been shown to accurately determine the scattering from interacting chains [28]. In addition, the model accounts for the micelle volume fraction, / m , and the contrast factor, 4SLD (4SLD = SLD s -SLD m , where SLD s is the scattering length density of the solvent and SLD m is the scattering length density of the micelle).…”

“…A polydispersity function was included to account for variations in the size of the micelle cross-section, hence the parameter r. The size distribution is calculated using a Schulz function parametrised with a polydispersity value of 0.15 [29]. For further information about the parametrisation of the flexible cylinder-PRISM model and about the calculation of the scattering length densities, please refer to previous publications [22,28].…”

Effect of Floor Cleaner Combination of Alcohol Ethoxylate-Sodium Lauryl Ether Sulfate and Combination of Carbol-Pine Oil on Ascaris lumbricoides Eggs

“…As a surfactant, SLES has bacteriostatic properties against gram-positive bacteria, is microbicidal against human immunodeficiency virus (HIV) type 1 and is functional but not effective in killing gram-negative bacteria. 28 Carbol and Pine Oil: Carbol or phenol is a disinfectant containing hydroxyl chemicals that bond to carbon atoms and form aromatic rings. Carbol has the chemical formula C6H5OH and is used as an antiseptic agent in surgical instruments in hospitals and as a cleaning agent for floors and toilets.…”