Coarse grained MD simulation of bulk and interfacial behavior of mixture of CTAB/SDS surfactants

CONTEXT

This study involves simulating the process of inhibiting corrosion through the formation of micelles by surfactants and their deposition on iron (Fe) surfaces. The primary focus is on examining CTAB/SDS mixtures in aqueous solutions with different concentrations. Micelle properties, including size, shape, aggregation number, cluster size, and surfactant diffusion, were calculated and validated with experimental data. The coarse-grained Fe surface was modeled and validated against experimental water contact-angle data. Subsequently, the deposition of CTAB/SDS mixtures on the Fe surface and air-water interface was studied systematically. We found that the relative ratio of CTAB/SDS in the solution directly influences surfactant deposition behavior, which might impact the corrosion inhibition efficiency.

METHODS

All the MD simulations were performed using the GROMACS software with MARTINI2 force field and Martini polar water. The molecules are packed using PACKMOL software. Both NVT and NPT simulations are caried out at temperature and pressure of 303 K and 1 bar respectively, with a nonbonded interaction cut-off (rcut) of 1.1 nm. The LJ potential was shifted from 0.9 nm to rcut, while the electrostatic potential was shifted from 0.0 nm to rcut. For electrostatics, reaction-field coulomb type is used, relative dielectric constant (epsilon-r) and the reaction field dielectric constant (epsilon-rf) are equal to 2.5 and infinity respectively. The dielectric constant below rcut is epsilon-r, and beyond the cut-off is epsilon-rf. Coulomb-modifier used as potential-shift which leads to shift in the coulomb potential by a constant such that it is zero at the rcut. This makes the potential of the integral of the force . The neighbor list was updated every 10 steps, employing a neighbor list cut-off equal to rcut. Using a polar water model, we used a constant time step of 0.02 ps throughout the simulation. The used epsilon-r = 2.5, is recommended for polar water.

Physico-chemical and spectroscopic investigation of flavonoid dispersed C n TAB micelles

In this study, kaempferol (0.2 m/mmol kg-1) dispersed cationic surfactant micelles were prepared as a function of alkyltrimethylammonium bromide (C n TAB) hydrophobicity (C = 12 to C = 16). The dispersion study of kaempferol in different C n TAB, i.e. dodecyltrimethylammonium bromide (C = 12), tetradecyltrimethylammonium bromide (C = 14) and hexadecyltrimethylammonium bromide (C = 16), was conducted with the physico-chemical properties of density, sound velocity, viscosity, surface tension, isentropic compressibility, acoustic impedance, surface excess concentration and area occupied per molecule and thermodynamic parameters Gibbs free energy, enthalpy and activation energy measured at 298.15 K. These properties were measured with varying concentration of C n TAB from 0.0260 to 0.0305 mol kg-1 in a 10% (w/w) aqueous dimethyl sulfoxide solvent system. The variations in these measured properties have been used to infer the kaempferol dispersion stability via hydrophobic-hydrophilic, hydrophilic-hydrophilic, van der Waals, hydrogen bonding and other non-covalent interactions.

Thermodynamics of the micellization of quaternary based cationic surfactants in triethanolamine-water media: a conductometry study

The effect of triethanolamine, a solvent with wide technical and industrial benefit on the micellization of an aqueous mixture of cationic surfactants, dodecyltrimethylammonium bromide (DETAB) and hexadecyltrimethylammonium bromide (HATAB) was studied to examining the stability of the mixed micelles at 298.1, 303.1, 308.1 and 313.1 K using the electrical conductance method. The values of the critical micelle concentration (C*) were found to decrease with an increase in the concentration of triethanolamine (TEA). The values of the free energy of micellization (ΔGm) were negative at a particular temperature, and the extent of spontaneity was discovered to increase when the concentration of TEA was increased. However, an increase in temperature was observed to have a negative linear relationship with the spontaneity of the process. The formation of the mixed micelles was an exothermic process, and it was also TEA and temperature-dependent with a trend similar to those observed in the free energy of micellization (ΔGm). The degree of disorderliness of the system was also found to be entropy driven at a higher concentration of TEA. The synergistic interaction between the molecules of DETAB–HATAB in the presence of TEA (0.4% v/v) and the spontaneity of the system was at the maximum at 0.1:0.9 mol fraction ratio and the energetics of the system was discussed based on hydrophobic–solvophobic interaction of the monomers in TEA at elevated temperatures.

Study on surface properties of sodiumdodecyl sulfate and dodecyltrimethylammonium bromide mixed surfactants and their interaction with dyes

The antagonistic as well as synergetic interaction for dodecyltrimethylammonium bromide (DTAB) and sodiumdodecyl sulfate (SDS) mixed surfactants by using surface tension are investigated on the basis of the results obtained earlier, the efficiency of adsorption (pC₂₀), aggregation number (N), ΓΓmax, effective Gibbs free energy (ΔGeffo) and CMCC20 are calculated additionally with three different temperatures at T = 293.15, 298.15 and 303.15 K as the detailed surface properties. The binding constants and standard free energy change of SDS and DTAB mixture with the interaction of (2.5× 10⁻⁵ mol L^–1 of methyl orange, MO and methylene blue, MB) are carried out by using UV-Vis spectroscopy at room temperature by using different models. The closer values of the binding constants and standard free energy change for SDS and DTAB mixture with the interaction of MO and MB are included in our investigations.

Hydrophobics of C n TAB in an aqueous DMSO-BSA nanoemulsion for the monodispersion of flavonoids

Herein, philicphobic interactions between flavonoids (quercetin, apigenin, and naringenin) and bovine serum albumin (BSA) were analyzed using physicochemical properties obtained at T = 298.15, 303.15, 308.15 K and 0.1 MPa, from 0.01 to 0.10 mol kg-1 of alkyl trimethyl ammonium bromide (C n TAB : DTAB, C n = 12; TDTAB, C n = 14; HDTAB, C n = 16). The flavonoids with cationic surfactants strongly interacted with BSA, as illustrated by the physicochemical parameters (PCPs), refractive index (n D), Walden product, pH, electrostatic potential and molar conductance (Λ m). Viscosity (η), density (ρ), η D, sound velocity (u) and specific conductance (k) data were used to calculate the relative viscosity (η r), viscous relaxation time (τ), Walden product, entropy (ΔS), enthalpy (ΔH), Gibbs free energy (ΔG), heat capacity (Δq) limiting dielectric constant (ε ∞), speed of light (C), acoustic impedance (Z) and molar refraction (R). These PCPs have quantitatively predicted the hydrophilic and hydrophobic (philicphobic) interactions developed are on increasing the alkyl chain (AC) of C n TAB. These interactions assist a monodispersion of the flavonoids, and a similar mechanism could equally be applicable to monodisperse the antioxidants in the aqueous nanoemulsions. Their philicphobic stoichiometry weakened the cohesive forces (CF) when the shear stress was increased, and enhanced surface activities were achieved that facilitated the flavonoids to interact with BSA due to intermolecular forces (IMF) to develop a stable nanoemulsion; Upon increasing the C n TAB concentrations, the n D value increases since the polarizability increases with stronger shear stress due to van der Waal forces and electrostatic interactions to achieve better flavonoid-BSA linkages.

Philic-phobic chemical dynamics of a 1st tier dendrimer dispersed o/w nanoemulsion

Olive, castor and linseed oil (oil-in-water) nanoemulsions were prepared using Tween-20, sodium dodecyl sulfate, and cetyltrimethylammonium bromide (0.12 w/w%) with 0.02 w/w% cellulose acetate propionate (CAP), 0.02 w/w% cellulose acetate butyrate (CAB), 6.2 w/w% ethyl acetate, 5.5 w/w% ethanol and 7.8 w/w% glycerol as dispersion agents. To study the dispersion effect of trimesoyl 1,3,5-tridimethyl malonate (TTDMM, 1st tier), nanoemulsions were prepared with olive, castor and linseed oil. Their density, viscosity, surface tension and friccohesity measurements at T = (293.15, 303.15, and 315.15) K, hydrodynamic radii, surface excess concentration, surface area per molecule, and antioxidant activities were studied. Dispersion variations of TTDMM on varying surfactant and specific interactions of the hydration spheres and ester moiety of TTDMM with ethyl acetate, ethanol and glycerol linked oil-water-surfactant networks have been established. The variations in physicochemical properties suggest that the oil-TTDMM interaction abilities of the surfactant and co-surfactant moieties in the nanoemulsions cause a hydrophobic segregation. The physicochemical study of both blank and TTDMM loaded nanoemulsions have illustrated the thermodynamic stabilities in terms of hydrophobic-hydrophilic, hydrophilic-hydrophilic, van der Waals and hydrogen bonding interactions.