Molecular Origins of Mesoscale Ordering in a Metalloamphiphile Phase

Controlling the assembly of soft and deformable molecular aggregates into mesoscale structures is essential for understanding and developing a broad range of processes including rare earth extraction and cleaning of water, as well as for developing materials with unique properties. By combined synchrotron small- and wide-angle X-ray scattering with large-scale atomistic molecular dynamics simulations we analyze here a metalloamphiphile–oil solution that organizes on multiple length scales. The molecules associate into aggregates, and aggregates flocculate into meso-ordered phases. Our study demonstrates that dipolar interactions, centered on the amphiphile headgroup, bridge ionic aggregate cores and drive aggregate flocculation. By identifying specific intermolecular interactions that drive mesoscale ordering in solution, we bridge two different length scales that are classically addressed separately. Our results highlight the importance of individual intermolecular interactions in driving mesoscale ordering

Subtle Effects of Aliphatic Alcohol Structure on Water Extraction and Solute Aggregation in Biphasic Water/<i>n</i>‑Dodecane

Organic phase aggregation behavior of 1-octanol and its structural isomer, 2-ethylhexanol, in a biphasic <i>n</i>-dodecane–water system is studied with a combination of physical measurement, small-angle X-ray scattering (SAXS), and atomistic molecular dynamic simulations. Physical properties of the organic phases are probed following their mixing and equilibration with immiscible water phases. Studies reveal that the interfacial tension decreases as a function of increasing alcohol concentration over the solubility range of the alcohol with no evidence for a critical aggregate concentration (cac). An uptake of water into the organic phases is quantified, as a function of alcohol content, by Karl Fischer titrations. The extraction of water into dodecane was further assessed as a function of alcohol concentration via the slope-analysis method sometimes employed in chemical separations. This method provides a qualitative understanding of solute (water/alcohol) aggregation in the organic phase. The physical results are supported by analyses of SAXS data that reveals an emergence of aggregates in <i>n</i>-dodecane at elevated alcohol concentrations. The observed aggregate structure is dependent on the alcohol tail group geometry, consistent with surfactant packing parameter. The formation of these aggregates is discussed at a molecular level, where alcohol–alcohol and alcohol–water H-bonding interactions likely dominate the occurrence and morphology of the aggregates