Complex formation in alkyldimethylamine oxide/sodium palmitate/water mixtures

Area of Science:

• Physical Chemistry
• Surfactant Science
• Materials Science

Background:

• Nonionic alkyldimethylamine oxides (CnDMAO) and sodium palmitate (NaPa) are key components in various formulations.
• Understanding their complex formation in solid and mixed micelle phases is crucial for predicting material properties.
• Regular Solution Theory (RST) provides a framework for analyzing non-ideal interactions in mixtures.

Purpose of the Study:

• To investigate the complex formation between CnDMAO (n=14, 16, 18) and NaPa in the solid phase.
• To determine the dependence of the RST interaction parameter (beta) on mixed micelle composition for C16DMAO/NaPa systems.
• To elucidate the nature of interactions between CnDMAO and NaPa in mixed micellar solutions.

Main Methods:

• Solid-phase complex formation was studied by analyzing dissolution temperature maxima.
• Mixed micelle composition and interactions were investigated using pyrene fluorescence measurements to determine critical micelle concentration (cmc).
• The RST interaction parameter (beta) was calculated from cmc and dissolution temperature depression data.

Main Results:

• Dissolution temperature showed maxima indicating complex formation, with compositions varying based on amine oxide chain length.
• Negative beta values were observed for all mixed systems, indicating non-ideal mixing.
• Analysis of beta values suggested short-range attractive interactions between the C16DMAO headgroup and palmitate anion.

Conclusions:

• Complex formation occurs in the solid phase of CnDMAO/NaPa mixtures, with composition dependent on CnDMAO chain length.
• Attractive interactions exist between CnDMAO and NaPa within mixed micelles, influencing their thermodynamic behavior.
• The study provides insights into the molecular interactions governing the properties of these surfactant mixtures.