The micellar property of mixed surfactant systems, cationic (dodecyltrimethylammonium bromide, DTAB) and anionic (sodium dodecylsulfate, SDS) surfactants with variable molar ratios in aqueous system has been reported by using surface tension and conductivity measurements at T = 293.15, 298.15 and 303.15 K. DTAB concentrations are varied from 1.0 × 10 −4 to 3 × 10 −4 mol l −1 in 1.0 × 10 −2 mol l −1 SDS solution while the SDS concentration is varied from 1.0 × 10 −3 to 1.5 × 10 −2 mol l −1 in approximately 5.0 × 10 −3 mol l −1 DTAB, so that such concentrations of DTAB-SDS (DTAB-rich) and SDS-DTAB (SDS-rich) solutions were chosen 3 : 1 ratio. The critical micellar concentration, as well as surface and thermodynamic properties for DTAB-rich and SDS-rich solutions, were evaluated by the surface tension ( γ ) and conductivity ( κ ) methods. The pseudo phase separation model was coupled with the dissociated Margules model for synergism. The Krafft temperature behaviour and optical analysis of mixed surfactants are studied using conductivity and UV–Vis spectroscopy, respectively. The dispersibility and stability of DTAB-rich and SDS-rich solutions with and without dyes (2.5 × 10 −5 mol l −1 of methyl orange and methylene blue) are carried out by using UV–Vis spectroscopy and dynamic light scattering.

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 (p C 20 ), aggregation number ( ), , effective Gibbs free energy ( ) and 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.

The physicochemical properties of Dodecyltrimethylammonium Bromide (DTAB) and Sodium Dodecylsulfate (SDS) rich surfactants in aqueous medium have been studied by surface tension, viscosity, density, and sound velocity at T = 293.15, 298.15, and 303.15 K. The DTAB concentration varies from 0.0001 to 0.03 mol · L−1 in the presence of ≈0.01 mol · L−1 SDS and the SDS concentration varies from 0.001 to 0.015 mol · L−1 in the presence of ≈0.005 mol · L−1 DTAB, so that the concentrations of cationic (DTAB‐rich) and anionic (SDS‐rich) solutions are taken in the ratio of 3:1. The density (ρ) and sound velocity (μ) data are used for calculating apparent molar volume (Vϕ), friccohesity (σ), isentropic compressibility (Ks,ϕ), surface tension (γ), and viscosity (η). These parameters reveals that the relative solute‐solvent and solute‐solute interactions of SDS‐DTAB and DTAB‐SDS in an aqueous medium with the help of physicochemical properties (PCPs).

The mixed micellization of aqueous binary mixtures of DTAB-rich and SDS-rich surfactants, comprising sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB) is studied in aqueous solution by using the physicochemical properties (PCPs) at three different temperatures (T = 293.15, 298.15, and 303.15 K) and P=0.1  MPa. The DTAB concentration is varied from 0.0001 to 0.03 M/mol·L−1 in the ∼0.01 M/mol·L−1 SDS solution, while the concentration of SDS is varied from 0.001 to 0.015 M/mol·L−1 in the ∼0.005 M/mol·L−1 DTAB. The stable formulations have been obtained by employing the DTAB-rich and SDS-rich surfactants solutions in 3 : 1 ratio. Therefore, different phases and aggregated states formed in the ternary combinations of DTAB/SDS/H2O have been identified and described. The calculated PCPs have been utilized for determining the nature of the solute-solvent interaction (SLS0I). With increasing surfactants concentration, the polarisation of the solution also increases along with an increase in relative viscosity (ηr), viscous relaxation time (τ), and surface excess concentration (Γmax). However, the surface area of the molecule (Amin), hydrodynamic volume (Vh), and hydrodynamic radius (Rh) decrease along with an increase in surfactants concentration.

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