Time‐Resolved SAXS Study of Polarity‐ and Surfactant‐Controlled Superlattice Transformations of Oleate‐Capped Nanocubes During Solvent Removal

Abstract

Structural transformations and lattice expansion of oleate‐capped iron oxide nanocube superlattices are studied by time‐resolved small‐angle X‐ray scattering (SAXS) during solvent removal. The combination of conductor‐like screening model for real solvents (COSMO‐RS) theory with computational fluid dynamics (CFD) modeling provides information on the solvent composition and polarity during droplet evaporation. Evaporation‐driven poor‐solvent enrichment in the presence of free oleic acid results in the formation of superlattices with a tilted face‐centered cubic (fcc) structure when the polarity reaches its maximum. The tilted fcc lattice expands subsequently during the removal of the poor solvent and eventually transforms to a regular simple cubic (sc) lattice during the final evaporation stage when only free oleic acid remains. Comparative studies show that both the increase in polarity as the poor solvent is enriched and the presence of a sufficient amount of added oleic acid is required to promote the formation of structurally diverse superlattices with large domain sizes.

High‐permittivity Solvents Increase MXene Stability and Stacking Order Enabling Ultraefficient Terahertz Shielding

“…This suggests a larger lattice displacement in samples cast from DMF. [ 41 ] From the SEM image of the cross‐section cut by FIB (Figure S10 , Supporting Information), films cast from DMF indeed show more disordered packing and porous defects compared to those from NMF and from DIW. From Figure 3c , the calculated d ‐spacing from the (002) peak in samples cast from DMF and NMF is ≈13.8 Å, higher than that from DIW (≈12.6 Å), which is caused by the larger molecule size of the organic intercalant than water.…”