Tag Archives: utkur mirsaidov

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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Nanodroplet Depinning from Nanoparticles

by Qi Liu, Fong Yew Leong, Zainul Aabdin, Utkarsh Anand, Tran Si Bui Quang, and Utkur Mirsaidov

ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b03078
Publication Date (Web): August 18, 2015

Nanoscale defects on a substrate affect the sliding motion of water droplets. Using in situ transmission electron microscopy imaging, we visualized the depinning dynamics of water nanodroplets from gold nanoparticles on a flat SiNx surface. Our observations showed that nanoscale pinning effects of the gold nanoparticle oppose the lateral forces, resulting in stretching, even breakup, of the water nanodroplet. Using continuum long wave theory, we modeled the dynamics of a nanodroplet depinning from a nanoparticle of comparable length scales, and the model results are consistent with experimental findings and show formation of a capillary bridge prior to nanodroplet depinning. Our findings have important implications on surface cleaning at the nanoscale.

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Direct observation of stick-slip movements of water nanodroplets induced by an electron beam

by Utkur Mirsaidov, Haimei Zheng, Dipanjan Bhattacharya, Yosune Casana, Paul Matsudaira

Proc Natl Acad Sci USA 109(19), 7187-7190 (2012)

Dynamics of the first few nanometers of water at the interface are encountered in a wide range of physical, chemical, and biological phenomena. A simple but critical question is whether interfacial forces at these nanoscale dimensions affect an externally induced movement of a water droplet on a surface.

At the bulk-scale water droplets spread on a hydrophilic surface and slip on a nonwetting, hydrophobic surface. Here we report the experimental description of the electron beam-induced dynamics of nanoscale water droplets by direct imaging the translocation of 10- to 80-nm-diameter water nanodroplets by transmission electron microscopy. These nanodroplets move on a hydrophilic surface not by a smooth flow but by a series of stick-slip steps.

We observe that each step is preceded by a unique characteristic deformation of the nanodroplet into a toroidal shape induced by the electron beam. We propose that this beam-induced change in shape increases the surface free energy of the nanodroplet that drives its transition from stick to slip state. 

Pictured is a snapshot of 50nm-diameter water droplet formed by the electron beam of a TEM. When irradiated with electrons, the droplet moves by a stick-slip mechanism in which the dome-shape droplet deforms into a high-energy toroidal shape and then translocates by extending a thin lamella from one edge.

Read online: PNAS.

Learn more about Utkur Mirsaidov‘s and Paul Matsudaira‘s research.