Fig. 3. Competitive ligand-mediated reconfiguring of jammed 2D assemblies of colloidal NCPSs at a liquid-liquid interface.

(A) The recruitment of 3K-PDMS-NH₂ and naked Fe₃O₄ NCs to the interface occurs on different time scales and depends on the relative concentration of each. These processes can be observed by monitoring the interfacial tension as a function of time for a pendant droplet of DMF suspended in a bath of PDMS/dodecane for systems configured with either 3K-PDMS-NH₂ (black squares), 3K-PDMS-NH₂ + Fe₃O₄ NCs (blue circles), or 3K-PDMS-NH₂ + Fe₃O₄ NCs + competitive ligand 1 (red triangles). [3K-PDMS-NH₂] = 5% w/w; [Fe₃O₄ NCs] = 0.5 mg ml⁻¹; [1] = 1 mg ml⁻¹. (B) The solid-like character of a buckled, 2D film of colloidal NCPSs is evidenced by wrinkling for droplets whose interface has been compressed upon droplet retraction. Only in the instance where competitive ligand 1 is present do the wrinkles in the film return to a smooth state, consistent with a dissipative process whereby the ligands promote the ejection of NCs from the film back into the bulk. Snapshots of such a reconfigurable droplet are shown at steady state, before retraction (top); immediately after droplet retraction (middle), where wrinkles appear; and after 20 min, whereupon the system has relaxed to an unwrinkled state (bottom). (C) Interfacial tension as a function of time for a pendant droplet of DMF suspended in a bath of PDMS/dodecane for systems configured with 3K-PDMS-NH₂ (5% w/w), Fe₃O₄ NCs (0.5 mg ml⁻¹), and varying concentrations of zwitterionic ligand 1 (0.5 to 5.0 mg ml⁻¹).