Dynamical dimer structure and liquid structure of fatty acids in their binary liquid mixture: dodecanoic and...

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Physics

Background:

• Fatty acids form dimers in liquid states.
• Understanding binary mixtures is crucial for materials science.
• Phase behavior and molecular interactions dictate mixture properties.

Purpose of the Study:

• To investigate the dimer structure and liquid structure of dodecanoic acid (LA) and 3-phenylpropionic acid (PPA) in a binary liquid mixture.
• To determine the self-assembly behavior of fatty acids in binary mixtures.
• To elucidate the phase behavior and molecular interactions within the LA/PPA system.

Main Methods:

• Differential Scanning Calorimetry (DSC) for thermal analysis.
• Measurement of self-diffusion coefficients (D) using NMR.
• Density and viscosity measurements.
• 13C NMR spin-lattice relaxation time analysis.
• Small-angle X-ray scattering (SAXS) and Small-angle Neutron Scattering (SANS) for structural analysis.

Main Results:

• The LA/PPA phase diagram shows a eutectic pattern, indicating complete immiscibility in the solid phase.
• Self-diffusion coefficients of LA and PPA remained distinct in the liquid phase, regardless of composition.
• SAXS and SANS data revealed the liquid structure of the binary mixture.
• Evidence suggests fatty acid dimers in the liquid phase consist of a single fatty acid species.

Conclusions:

• Fatty acid dimers in the liquid phase of the LA/PPA binary mixture are homodimers (composed of the same fatty acid species).
• Complete immiscibility in the solid phase does not necessitate mixing at the dimer level in the liquid phase.
• The study provides insights into the structural organization and interactions of fatty acids in binary mixtures.