Apparent molar volume, apparent molar adiabatic compressibility, and solubilization studies of aqueous solutions of sodium p-(n-dodecyl)benzenesulfonate as a function of surfactant and solubilizate concentrations and temperature

Molecular mechanism underlying the effects of temperature and pH on the size and surface charge of octenylsuccinated oat β-glucan aggregates

Environmental temperature and pH induced significant changes in the size and surface charge (ζ) of octenylsuccinated oat β-glucan aggregates. The underlying mechanisms were explored by using ¹H-NMR, fluorescence spectra, thermodynamic analysis, and SAXS. At pH 6.5, the size decreased with temperature while ζ continuously increased. With increasing pH at 293 K, parabolic and U-shaped trends were observed in the size and ζ, peaking at pH 8.5 and 6.5, respectively. At any tested pH, the size decreased with temperature. Overall, ζ significantly increased with temperature at each pH. As temperature increased, the compactness of hydrophobic-domains increased while the compactness of hydrophilic-domains decreased. In an acidic environment, both the compactness increased with decreasing pH, but in an alkaline environment, they decreased with pH. The compactness changes were co-driven by enthalpy and entropy and corresponded to changes in the hydrophobic interactions in hydrophobic-domains, hydrogen bonds in hydrophilic-domains and electrostatic repulsions among octenylsuccinate molecules.

Mixed micelles of sodium 4-decyl naphthalene sulfonate with Triton X-100 and sodium dodecyl sulfonate analyzed by 1H NMR

The characteristics of sodium 4-decyl naphthalene sulfonate (SDNS)/Triton X-100 (TX-100) and sodium dodecyl sulfonate (SDSN)/SDNS mixed micelles with different molar ratios were studied by 1D and 2D 1H NMR. In the mixed micelle of SDNS/TX-100 the phenoxy rings of the TX-100 are embedded in the near vicinity of the alkyl chains of SDNS and its polyoxyethylene segments, but the first oxyethylene group, to which the phenoxy ring is adjacent, are located near the naphthyl rings. In the mixed micelle of the SDNS/SDSN system the sulfonate groups of SDSN are embedded in the naphthyl rings of SDNS; i.e., they are located more internally in the mixed hydrophobic micellar core than those of SDNS. Moreover, the naphthyl rings of SDNS separating these sulfonate groups of SDSN may play an active role in weakening the electrostatic repulsion of the negatively charged sulfonate groups, which favors the mixed micelle aggregation.