posted on 2020-08-12, 21:18authored byYige Gao, Paul Y. Kim, David A. Hoagland, Thomas P. Russell
Jammed
packings of bidisperse nanospheres were assembled on a nonvolatile
liquid surface and visualized to the single-particle scale by using
an in situ scanning electron microscopy method. The
PEGylated silica nanospheres, mixed at different number fractions
and size ratios, had large enough in-plane mobilities prior to jamming
to form uniform monolayers reproducibly. From the collected nanometer-resolution
images, local order and degree of mixing were assessed by standard
metrics. For equimolar mixtures, a large-to-small size ratio of about
1.5 minimized correlated metrics for local orientational and positional
order, as previously predicted in simulations of bidisperse disk jamming.
Despite monolayer uniformity, structural and depletion interactions
caused spheres of a similar size to cluster, a feature evident at
size ratios above 2. Uniform nanoparticle monolayers of high packing
disorder are sought in many liquid interface technologies, and these
experiments outlined key design principles, buttressing extensive
theory/simulation literature on the topic.