Mixed aquo-organic solvents are used in chemical, industrial, and pharmaceutical processes along with amphiphilic materials. Their fundamental studies with reference to bulk and interfacial phenomena are thus considered to be important, but such detailed studies are limited. In this work, the interfacial adsorption of sodium dodecylsulfate (SDS, C12H25SO4(-)Na(+)) in dioxane-water (Dn-W) and methanol-water (Ml-W) media in extensive mixing ratios along with its bulk behavior have been investigated. The solvent-composition-dependent properties have been identified, and their quantifications have been attempted. The SDS micellization has been assessed in terms of different solvent parameters, and the possible formation of an ion pair and triple ion of the colloidal electrolyte, C12H25SO4(-)Na(+) in the Dn-W medium has been correlated and quantified. In the Ml-W medium at a high volume percent of Ml, the SDS amphiphile formed special associated species instead of ion association. The formation of self-assembly and the energetics of SDS in the mixed solvent media have been determined and assessed using conductometry, calorimetry, tensiometry, viscometry, NMR, and DLS methods. The detailed study undertaken herein with respect to the behavior of SDS in the mixed aquo-organic solvent media (Dn-W and Ml-W) is a new kind of endeavor.

The influence of water-insoluble nonionic triblock copolymer PEO-PPO-PEO [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] i.e., E6P39E6 with molecular weight 2800, on the microstructure and self-aggregation dynamics of anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution (D2O) were investigated using high resolution nuclear magnetic resonance (NMR) and small-angle neutron scattering (SANS) measurements. Variable concentration and temperature proton ((1)H), carbon ((13)C) NMR chemical shifts, (1)H self-diffusion coefficients, (1)H spin-lattice and spin-spin relaxation rates data indicate that the higher hydrophobic nature of copolymer significantly influenced aggregation characteristics of SDS. The salient features of the NMR investigations include (i) the onset of mixed micelles at lower SDS concentrations (<3 mM) relative to the copolymer-free case and their evolution into SDS free micelles at higher SDS concentrations (~30 mM), (ii) disintegration of copolymer-SDS mixed aggregate at moderate SDS concentrations (~10 mM) and still binding of a copolymer with SDS and (iii) preferential localization of the copolymer occurred at the SDS micelle surface. SANS investigations indicate prolate ellipsoidal shaped mixed aggregates with an increase in SDS aggregation number, while a contrasting behavior in the copolymer aggregation is observed. The aggregation features of SDS and the copolymer, the sizes of mixed aggregates and the degree of counterion dissociation (α) extracted from SANS data analysis corroborate reasonably well with those of (1)H NMR self-diffusion and sodium ((23)Na) spin-lattice relaxation data.

The influence of the water soluble non-ionic tri-block copolymer PEO-PPO-PEO [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] i.e., E2P16E2 (L31) on the microstructure and self-aggregation dynamics of the anionic surfactant sodium dodecylsulfate (SDS) in aqueous solution was investigated using cloud point (CP), isothermal titration calorimetry (ITC), high resolution nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR), and small-angle neutron scattering (SANS) measurements. CP provided the thermodynamic information on the Gibbs free energy, enthalpy, entropy and heat capacity changes pertaining to the phase separation of the system at elevated temperature. The ITC and NMR self-diffusion measurements helped to understand the nature of the binding isotherms of SDS in the presence of L31 in terms of the formation of mixed aggregates and free SDS micelles in solution. EPR analysis provided the micro-viscosity of the spin probe 5-DSA in terms of rotational correlation time. The SANS study indicated the presence of prolate ellipsoidal mixed aggregates, whose size increased with the increasing addition of L31. At a large [L31], SANS also revealed the progressive decreasing size of the ellipsoidal mixed aggregates of SDS-L31 into nearly globular forms with the increasing SDS addition. Wrapping of the spherical SDS micelles by L31 was also corroborated from (13)C NMR and SANS measurements.

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Interaction of the copolymer L61 i.e., (EO)2(PO)32(EO)2 (where EO and PO are ethylene and propylene oxides, respectively) with the surfactant SDS (Sodium Dodecylsulfate) in relation to their self-aggregation, dynamics and...

Physicochemical studies on aqueous mixtures of ionic liquids (ILs) and reverse pluronics are limited. Self-aggregation dynamics and microstructure of a surface-active IL (SAIL), 1-butyl-3-methylimidazolium octylsulfate [C 4 mim] [C 8 OSO 3 ], in the presence of a reverse pluronic, PO 8 EO 22 PO 8 (known as 10R5), were studied using isothermal titration calorimetry (ITC), high-resolution nuclear magnetic resonance (NMR), and small-angle neutron scattering (SANS) methods. Also, cryo-/freeze-fracture transmission electron microscopy was employed to determine the microstructures of SAIL/10R5 mixtures. The ITC and NMR results revealed facilitation of SAIL aggregation in the presence of 10R5 forming mixed aggregates as well as free SAIL micelles. 2 H spin relaxation rate data pointed out the onset of slow dynamics of the aqueous SAIL/10R5 mixture with an increase in either the former or the latter. Globular morphologies of the mixed species as well as their individual components were corroborated from the measurements. The preferential location of interaction of the SAIL with the 10R5 was identified from 13 C NMR chemical shift findings to be in the interfacial region of the assembled SAIL. The formed species were mixed interacted aggregates but not mixed micelles that arise from mixed surfactants. The physicochemical information acquired herein would enrich the literature on the 10R5/SAIL mixed microheterogeneous systems having importance in the making of useful green drug carrier systems and templates for the synthesis of nanomaterials.

The detailed aggregation behavior of sodiumdodecyl sulfate (SDS) in tetrahydrofuran (Tf)-water (W) and formamide (Fa)-water (W) media at varied volume percent compositions has been investigated. Surface tension (ST), conductance (Cond), viscosity (Visc), isothermal titration calorimetry (ITC), nuclear magnetic resonance (NMR) and small angle neutron scattering (SANS) were used in this study. The presence of nonaqueous solvents affected the critical micelle concentration (CMC) of SDS, the counter-ion binding of the micelle, the energetics of the air/water interfacial adsorption and micellization of the amphiphiles in the bulk, the ion-association (ion-pair, triple-ion, quadruple, etc. between Na(+) and DS(-) ions) as well as the weakly soluble (aggregation less) amphiphile solution. Tf has been observed to produce a "dead zone" or "non-micelle formation zone" in the mixed Tf-W domain of 10-40 vol%. Fa influenced the SDS aggregation up to 70 vol%, at higher proportions (below the Krafft temperature (K(T))), instead of the micelle, "randomly arranged globular assembly" (RAGA) was formed. The correlation of the standard free energy of micellization (ΔG(m)(0)) with different solvent parameters (1) dielectric constant (ε), (2) viscosity (η0), (3) Reichardt parameter (E(T)(30)), (4) Gordon parameter (G), and (5) Hansen-Hildebrand hydrogen bonding parameter (δ(h)) has been attempted. It has been found that δ(h) produced a master correlation between ΔG(m)(0) and δ(h) for different binary mixtures such as Tf-W, Fa-W, Ml-W and Dn-W.

Subtle changes in the microstructure and dynamics of the triblock copolymer L121, (ethylene oxide) (propylene oxide) (ethylene oxide)i.e., EPE, and sodium dodecylsulfate (SDS) system in aqueous medium were investigated using high-resolution nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and small-angle neutron scattering (SANS) methods. NMR self-diffusion measurements helped us to understand the nature of binding of SDS with L121, and the formation of their mixed aggregates. These results showed that even at low [SDS] (∼2 mM), the addition of L121 stabilized the dynamics of SDS. Furthermore, the increase in [SDS] resulted in progressive changes in the diffusion behavior of both SDS and L121. C chemical shift analysis revealed that preferential binding of L121 occurred on the SDS micelle surface. Deuterium (H) NMR spin-relaxation data evidenced that the formed mixed aggregates were non-spherical in terms of relaxation rate changes, and slowed the dynamics. The rotational correlation times of mixed aggregates were estimated from EPR analysis. A SANS study indicated the presence of uni- and multi-lamellar vesicles of L121 at low [SDS]. The vesicles transformed to mixed L121-SDS micelles in the presence of a higher [SDS]. This was supported by the measurements of H NMR spin-relaxation and EPR rotational correlation times.