Hydration Layer-Mediated Pairwise Interaction of Nanoparticles

Utkarsh Anand†‡§∥, Jingyu Lu†‡§∥, Duane Loh†‡, Zainul Aabdin†‡§∥, and Utkur Mirsaidov*†‡§∥

Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117551
Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore, 117543
§ Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546
NanoCore, National University of Singapore, 4 Engineering Drive 3, Singapore 117576

Nano Lett., Article ASAP DOI: 10.1021/ acs.nanolett.5b04808 Publication Date (Web): December 28, 2015

When any two surfaces in a solution come within a distance the size of a few solvent molecules, they experience a solvation force or a hydration force when the solvent is water. Although the range and magnitude of hydration forces are easy to characterize, the effects of these forces on the transient steps of interaction dynamics between nanoscale bodies in solution are poorly understood. Here, using in situ transmission electron microscopy, we show that when two gold nanoparticles in water approach each other at a distance within two water molecules (∼5 Å), which is the combined thickness of the hydration shell of each nanoparticle, they form a sterically stabilized transient nanoparticle dimer. The interacting surfaces of the nanoparticles come in contact and undergo coalescence only after these surfaces are fully dehydrated. Our observations of transient steps in nanoparticle interactions, which reveal the formation of hydration layer mediated metastable nanoparticle pairs in solution, have significant implications for many natural and industrial processes.

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