Accurate measurement of the molecular thickness of thin organic shells on small inorganic cores using dynamic light scattering

Shortell, Matthew P., Fernando, Joseph F. S., Jaatinen, Esa A., & Waclawik, Eric R. (2014) Accurate measurement of the molecular thickness of thin organic shells on small inorganic cores using dynamic light scattering. Langmuir, 30(2), pp. 470-476.

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Dynamic light scattering (DLS) has become a primary nanoparticle characterization technique with applications from materials characterization to biological and environmental detection. With the expansion in DLS use from homogeneous spheres to more complicated nanostructures, comes a decrease in accuracy. Much research has been performed to develop different diffusion models that account for the vastly different structures but little attention has been given to the effect on the light scattering properties in relation to DLS. In this work, small (core size < 5 nm) core-shell nanoparticles were used as a case study to measure the capping thickness of a layer of dodecanethiol (DDT) on Au and ZnO nanoparticles by DLS. We find that the DDT shell has very little effect on the scattering properties of the inorganic core and hence can be ignored to a first approximation. However, this results in conventional DLS analysis overestimating the hydrodynamic size in the volume and number weighted distributions. By introducing a simple correction formula that more accurately yields hydrodynamic size distributions a more precise determination of the molecular shell thickness is obtained. With this correction, the measured thickness of the DDT shell was found to be 7.3 ± 0.3 Å, much less than the extended chain length of 16 Å. This organic layer thickness suggests that on small nanoparticles, the DDT monolayer adopts a compact disordered structure rather than an open ordered structure on both ZnO and Au nanoparticle surfaces. These observations are in agreement with published molecular dynamics results.

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3 citations in Web of Science®
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ID Code: 69514
Item Type: Journal Article
Refereed: Yes
Additional Information: Funding was provided by the Asian Office of Aerospace Research and Development (AOARD). Grant ID: AOARD-13-4016
Keywords: ZnO, Dynamic Light Scattering, Core-shell nanoparticles, Au
DOI: 10.1021/la403391t
ISSN: 1520-5827
Subjects: Australian and New Zealand Standard Research Classification > PHYSICAL SCIENCES (020000) > OPTICAL PHYSICS (020500) > Nonlinear Optics and Spectroscopy (020503)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2014 American Chemical Society
Deposited On: 28 Mar 2014 00:40
Last Modified: 08 Dec 2014 17:49

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