Nanocrystal colloidal gel networks have attracted interest due to their potential to exhibit reconfigurable structure and tunable properties. By retaining the distinctive properties of single nanocrystals in a colloidal assembly modified in new and desirable ways due to synergistic contributions, such gel networks are a promising materials platform. Gels may be created by inducing entropic, attractive interactions between dispersed nanoparticles with a non-adsorbing, secondary macromolecule or depletant. Due to the depletant’s non-adsorbing nature, depletion gelation offers the opportunity to functionalize the nanocrystal surface independently from the source of attractions. The introduction of this second interaction to the system can act as an effective ‘knob’ to tune the assembled gel microstructure and thereby control its resulting properties. Here, we probe the effect of steric and electrostatic contributions from polymers wrapping the nanocrystal surface on the resulting gel structure. Colloidal indium oxide nanocrystals were stripped of their native, hydrophobic ligands and subsequently wrapped with copolymers of polyacrylic acid grafted with polyethylene oxide, offering tunable charge and steric bulk. Small angle X-ray scattering was then employed to analyze structural differences upon depletant addition. Understanding how these short-ranged repulsions affect gelation is critical for controlling network assembly and presents an avenue to exploit functional surface polymers to impart new, structure-dependent properties in nanocrystal gels.

Influence of surface functionalization on the structure of nanocrystal gels assembled with depletion attractions

ACS Spring 2022

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