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Midlothian, VA, United States

Shirk K.,Purdue University | Steiner C.,Purdue University | Kim J.W.,Hanyang University | Marquez M.,YNano LLC | Martinez C.J.,Purdue University

We investigated the assembly of colloidal silica crystals inside double emulsion drops generated in microcapillary microfluidic devices. The double emulsions are composed of an aqueous suspension of monodisperse silica particles in the inner drop surrounded by a PDMS oil drop that acts as a semipermeable membrane for the diffusion of water into or out of the inner drop in the presence of an osmotic gradient. Imposing a high osmotic pressure in the continuous phase induces water diffusion out of the inner drop, increasing the silica volume fraction (φsilica) and leading to the formation of a spherical colloidal silica crystal. Silica suspensions with no salt or low salt concentration (<10-3 M) formed colloidal crystals with φsilica up to 0.68. Monodisperse spherical colloidal silica crystals with sizes ranging from 16 to 133 μm were generated by varying the device geometry, flow-rate ratios, and initial silica fraction. At salt concentrations > 10-3 M, the electrostatic repulsion is reduced, and crystallization is suppressed. Crystals were preserved in a hydrogel matrix or inside a silicone rubber shell. This study demonstrates a robust path for controlled colloidal assembly inside double emulsion drops. © 2013 American Chemical Society. Source

Hu M.,University of Central Florida | Hu M.,Hewlett - Packard | Ghoshal A.,University of Central Florida | Marquez M.,YNano LLC | Kik P.G.,University of Central Florida
Journal of Physical Chemistry C

We present an experimental study of the tunability of the silver nanoparticle localized plasmon resonance in close proximity to a gold film. Broad-band tuning of the silver particle plasmon resonance from blue wavelengths into the near-IR region can be achieved due to strong electromagnetic coupling between the nanoparticle and the metal film. When the thickness of a thin silica spacer layer between the metal nanoparticle and the metal film is altered, the resonance frequency shifts. Single particle spectroscopy of over 250 isolated silver nanoparticles revealed evidence for the excitation of both horizontal and vertical plasmon modes. Distinct resonance features observed in the scattering spectra were assigned to specific modes based on a dipole-dipole interaction model. The experimental results suggest that low-loss silver nanoparticles can be used in surface-enhanced spectroscopy studies throughout the entire visible spectrum. The use of frequency-tuned spherical metal nanoparticles on solid substrates could lead to thermally stable substrates for plasmon-enhanced sensing applications, including surface-enhanced Raman scattering and refractive index based biodetection methods. © 2010 American Chemical Society. Source

Smoukov S.K.,North Carolina State University | Smoukov S.K.,University of Cambridge | Tian T.,North Carolina State University | Vitchuli N.,Xanofi Inc. | And 7 more authors.
Advanced Materials

A simple process for batch or continuous formation of polymer nanofibers and other nanomaterials in the bulk of a sheared fluid medium is introduced. The process may be of high value to commercial nanotechnology, as it can be easily scaled up to the fabrication of staple nanofibers at rates that may exceed tens of kilograms per hour. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Rincon L.,U.S. National Institute of Standards and Technology | Rincon L.,University of Los Andes, Venezuela | Hasmy A.,U.S. National Institute of Standards and Technology | Hasmy A.,Simon Bolivar University of Venezuela | And 3 more authors.
Chemical Physics Letters

We introduce a non-self-consistent energy correction that is based on the fluctuation of the density into the tight-binding method to show that a parameterization derived only from crystal electronic structure data can describe the ground state structures of small clusters containing noble metal atoms and the turnover from a planar to a nonplanar structure. The efficiency and robustness of the method is illustrated by comparing the resulting corrected and uncorrected global minimum energy configurations of neutral gold clusters, Au n , with Density Functional Theory calculations. © 2010 Elsevier B.V. All rights reserved. Source

Liu J.,Virginia Commonwealth University | Shen Z.,CAS Beijing National Laboratory for Molecular | Lee S.-H.,Dong - A University | Marquez M.,YNano LLC | McHugh M.A.,Virginia Commonwealth University
Journal of Supercritical Fluids

Electrospinning is combined with the PCA (precipitation with a compressed fluid antisolvent) process (ES-PCA) to produce micron to submicron polymeric fibers with open-cell or hollow core morphology. CO2 is used as the compressed gas of choice and the impact of CO2 pressure (density) on fiber morphology is demonstrated for the poly(vinyl pyrrolidone) (PVP)-dichloromethane, PVP-ethanol, poly(vinylidenefluoride) (PVDF)-dimethylacetamide, and PVDF-dimethyl formamide systems. CO2, which is in excess for this process, rapidly extracts solvent from the surface of the liquid jet to form a vitrified polymer skin and also dissolves into the liquid jet and induces the polymer-solvent solution to phase separate. The ES-PCA technique has the advantage that fiber morphology can be easily controlled via pressure and pressures in excess of 100 bar are not needed to obtain a variety of different fiber morphologies. The fiber formation process correlates closely with the binary solvent-CO2 and ternary polymer-solvent-CO2 phase behavior. © 2010 Elsevier B.V. All rights reserved. Source

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