X-ray characterization of three possible edible oleogelators: Experiment
and Theory
Abstract
Three oleogeletors molecules (Triacontane (TC), Stearic acid (SA), and
Behenyl Lignocerate (BL)) were studied individually, in pairs, or all
together to make an oleogel using triolein as the oil. WAXS, SAXS and
USAXS were used to elucidate the solid structures from angstroms to a
few micrometers. A two-dimensional mapping of atomic positions for each
molecule was carried out to understand the crystalline multilayer
structures formed. We assumed that the molecules were rigidly extended
and that they underwent no significant (hindered) rotations so that the
free energy is determined by the Lennard-Jones interactions of
closely-packed multilayers. TC molecules were predicted to form a tilt
angle of θt ≈ 33°, yielding a SAXS line at q≈ 0.194
Å-1, in acceptable agreement with the measured q=0.181
Å-1.For SA crystals θt ≈ 33°
(predicted) yielding a SAXS line at q=0.150 Å-1
compared to q=0.159 Å -1 (observed). No mixed crystals
were observed for any pair of molecules or when all three were used.
USAXS data showed that SA forms large nanocrystals compared to TC and
BL. All three combinations of molecular pairs showed basic scatterers
smaller or similar to those of individual molecules. The theory
presented here, together with the experimental results, showed why no
mixed crystals are formed from two or all three molecules. Data from the
USAXS region suggested that, when using all three molecules, a more
compact fractal structure was obtained, compared with those if one or
two of the molecules were used.