Molecular Origins of Mesoscale Ordering in a Metalloamphiphile Phase

Abstract

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.

Complexation Enhancement Drives Water‐to‐Oil Ion Transport: A Simulation Study

“…The amount of nitrate counterions (− e ) directly bound to each Ln III (+3 e ) is calculated to be around 2.9±0.5 for Ce 3+ and 2.9±0.6 for Yb 3+ , indicating that Ln III ions are nearly (∼97 %) charge neutralized by nitrates in organic phases. This decreases the electrostatic repulsion and allows the metalloamphiphile complexes to aggregate; a phenomenon that we recently investigated using small angle X‐ray scattering measurements . Very recently it was experimentally demonstrated that aggregates in metalloamphiphile‐in‐organic solutions are not strictly charge neutral …”

“…The four solutions were studied using all‐atom, explicit‐solvent MD simulations with a polarizable force field. To guarantee that our systems were well equilibrated, annealing simulations were performed followed by production simulations, which were run longer than the previous atomistic simulations using polarizable force field ,…”

“…The aggregation behavior plays a significant role in the metal extraction process. For instance, the interactions between Ln III ‐centered aggregates have been found to be able to affect the morphologies of the Ln III ‐centered aggregates in organic phases: strong inter‐cluster interactions were able to drive large clusters with more than one lanthanide ions . Moreover, the difference in the ionic radius between Ce III and Yb III (the lanthanide contraction) has been shown to be able to manifest beyond their coordination spheres in driving the mesoscale ordering in organic phases and consequently influence the Ln III extraction efficiency .…”

“…The system energy was minimized using the steepest descent method for 1 ps and followed by the conjugate gradient for 1 ps. The annealing simulations were then performed to speed up the aggregation behavior . In the annealing simulations, the temperature was elevated from 298 K to 360 K within the duration of 0.1 ns, stayed at 360 K for a duration of 2.3 ns, dropped to 298 K within 0.1 ns, and was maintained at 298 K for 0.5 ns.…”

“…By calculating the small‐angle X‐ray scattering using large scale atomistic MD simulations, and comparing with the experimental data from synchrotron X‐ray scattering technique, we have recently shown that the dipolar interactions between the Eu 3+ ‐centered aggregates drive the mesoscale assembly in the organic phase . The mesoscale assembly plays a significant role in the ion transport .…”