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Colloidal Dispersion of Gold Nanorods: Historical Background, Optical Properties, Seed-Mediated Synthesis, Shape Separation and Self-Assembly

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Colloidal Dispersion of Gold Nanorods: Historical Background, Optical Properties, Seed-Mediated Synthesis, Shape Separation and Self-Assembly Materials Science and Engineering R 65 (2009) 1–38 Contents lists available at ScienceDirect Materials Science and Engineering R journal homepage: www.elsevier.com/locate/mser Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly Vivek Sharma a,1, Kyoungweon Park a,2, Mohan Srinivasarao a,b,c,* a School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States of America b School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, United States of America c Center for Advanced Research on Optical Microscopy (CAROM), Georgia Institute of Technology, Atlanta, GA 30332, United States of America ARTICLE INFO ABSTRACT Article history: The color of colloidal dispersions of gold particles in a fluid, typically water, varies from red to blue, Available online 28 April 2009 depending upon the shape and size of particles. The color and optical properties of gold nanoparticles originate from localized surface plasmons, and are sensitive to their local dielectric environment. Unlike Keywords: nanospheres, the optical properties, hydrodynamic behavior as well as phase behavior of nanorods are Gold Nanorods influenced by their shape anisotropy. Thus, rods have an additional absorption peak, possess very Plasmon resonance different dynamics (affects sedimentation) and their concentrated dispersions form liquid crystalline Self Assembly phases. In this review, we focus on presenting the essential shape dependent optics, as well as the Nanocomposites hydrodynamics and phase behavior of rod-like gold nanoparticles. We reveal our methodology for Seed-mediated synthesis making less polydisperse nanorods sols by using an optimized seed-mediated synthesis (controlled Evaporative drying chemistry), followed by shape separation by centrifugation (based on our hydrodynamics arguments). We elucidate the role of Brownian motion in determining colloidal stability and sedimentation behavior, and describe patterns formed by drying mediated assembly on glass slides and TEM grids. We outline early studies (before 1930) of gold sols that are not only instructive in learning about synthesis and physical properties of gold nanoparticles, but show how the study of colloidal gold established many key principles in colloidal science. ß 2009 Elsevier B.V. All rights reserved. Contents 1. Introduction . 2 2. Historical perspective on colloidal gold sols. 3 2.1. Faraday’s experiments on synthesis and color of ruby gold. 3 2.2. Synthesis of gold sols, including seed-mediated method . 3 2.3. Size and shape dependent color of gold sols . 4 2.4. Scattering and absorption: Mie theory for spherical, and Gans theory for ellipsoidal particles . 4 2.5. Shape effects on Brownian motion: sedimentation, diffusion and viscosity . 5 2.6. Colloidal stability, ‘gold number’ and protective action of macromolecules . 6 2.7. Other metal nanoparticles and inorganic lyotropic liquid crystals . 6 2.8. Recent interest in colloidal gold . 6 3. Colloidal nature of gold . 6 4. Optical properties of gold nanoparticles. 8 4.1. Genesis of extinction spectrum . 8 4.2. Localized surface plasmon resonance for spherical particles . 9 4.3. Plasmon resonance for ellipsoidal nanoparticles . 10 4.4. Beyond dipole resonance and beyond electrostatics . 10 * Corresponding author at: School of Polymer, Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States of America. E-mail address: [email protected] (M. Srinivasarao). 1 Current address: Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave, Bldg 3-249, Cambridge, MA 02139, United States. 2 Current address: Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433-7702, United States. 0927-796X/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mser.2009.02.002 2 V. Sharma et al. / Materials Science and Engineering R 65 (2009) 1–38 4.5. Computational methods. 11 4.6. Absorption spectrum of colloidal dispersions of gold nanorods . 11 4.7. Local field enhancements and sensing applications . 11 4.8. Color of colloidal dispersions of gold nanorods . 12 4.9. Polarization dependent color and absorption in polymer–gold nanocomposite films . 13 4.10. The ultramicroscope. 13 5. Synthesis of gold nanorods . 15 5.1. Recipe for nanorod synthesis using seed-mediated method with binary surfactant . 16 5.2. Effect of surfactant ‘counter-ion’ on morphology of nanoparticles . 17 5.3. The role of binary surfactant and precursor complexes . 18 5.4. Role of ascorbic acid (AA) as a reducing agent . 20 5.5. Effect of temperature on growth . 21 5.6. The role of supersaturation in producing monodisperse sols. 21 6. Shape separation of colloidal gold nanorods . 23 6.1. Theoretical aspects of sedimentation of rods and spheres . 23 6.2. Separation of nanorods from spherical nanoparticles using centrifugation. 24 6.3. Separation of nanorods with different aspect ratio . 25 7. Self-assembly of rod-like nanoparticles . 26 7.1. Lyotropic liquid crystals from inorganic colloidal particles . 26 7.2. Liquid crystalline behavior of spherocylinders . 27 7.3. Coffee ring-like pattern formation with rod-like particles . 28 7.4. Concentric birefringent bands on glass slide: Liesegang ring like patterns . 29 7.5. Self-assembly on TEM grids. 32 7.5.1. Two-dimensional phase transitions observed in self-assembly on a TEM . 32 7.5.2. Heterogeneity and polydispersity of the sample . 33 7.5.3. Patterns formed by evaporation . 34 8. Synopsis and outlook. ..
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