Topic
Particle
About: Particle is a research topic. Over the lifetime, 96582 publications have been published within this topic receiving 1954327 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: The discrete dipole approximation is used to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces.
Abstract: We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest /E/2 values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given /E/2 is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest /E/2 values we have calculated for spacings of 2 nm or more is approximately 10(5).
1,778 citations
TL;DR: In this paper, the effect of size and shape on the spectral response of individual silver nanoparticles was studied and it was shown that specific geometrical shapes give distinct spectral responses.
Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources cove...
1,687 citations
TL;DR: In this article, the relative motion correlations for dispersed two-phase flows of bubbles, drops, and particles were developed from simple similarity criteria and a mixture viscosity model, and satisfactory agreements were obtained at wide ranges of the particle concentration and Reynolds number.
Abstract: Drag coefficient and relative motion correlations for dispersed two-phase flows of bubbles, drops, and particles were developed from simple similarity criteria and a mixture viscosity model. The results are compared with a number of experimental data, and satisfactory agreements are obtained at wide ranges of the particle concentration and Reynolds number. Characteristics differences between fluid particle systems and solid particle systems at higher Reynolds numbers or at higher concentration regimes were successfully predicted by the model. Results showed that the drag law in various dispersed two-phase flows could be put on a general and unified base by the present method.
1,685 citations
Book•
01 Jan 1968
TL;DR: In this paper, the authors proposed a method of particle size distribution determination based on the Coulter principle, which is the alternative derivation of Kozeny's equation using equivalent capillaries.
Abstract: Sampling of powders sampling of dusty gases in gas streams sampling and sizing from the atmosphere - air technology, Atcor Net 2000, Bausch and Lomb, Beckman, Centre for Air Environmental Studies, Climet Series 7000, Coulter Model 550 contamination monitor, Dynac, Gardner, GCA Miniram, Insitec PCSV-P, Kratel Partoscope, Leitz Tyndalloscope, Met One particle counters, Pacific Scientific Hiac/Royco particle counting systems, particle measuring systems, RAC particle monitors, Rotheroe and Mitchell digital dust indicator, Saab photometer, Sartorius, Sinclair Particle size, shape and distribution - shape regeneration by Fourier analysis, the Rosinn-Rammler distribution, mean particle sizes and specific surface evaluation for Rosinn-Rammler distribution Sieving microscopy interaction between particles and fluids in a gravitational field dispersion of powders incremental methods of particle size determination cumulative methods of sedimentation size analysis fluid classification - the Warmain cyclosizer, the Humboldt particle size analyzer TDS, the cross-flow elbow classifier, the Bahco classifier, the BCURA centrifugal elutriator, Analysette 9, the Donaldson classifier, the Micromeritics classifier Centrifugal methods - early instruments - the Marshall centrifuge and the MSA particle size analyser, the Alpine sedimentation centrifuge, the Mikropul Sedimentputer, the LADAL X-ray centrifuge, the LADAL pipette withdrawal centrifuge The electrical sensing zone method of particle size distribution determination (the Coulter principle) radiation scattering methods of particle size determination high-order Tyndall spectr (HOTS) permeametry and gas diffusion - alternative derivation of Kozeny's equation using equivalent capillaries Gas adsorption - BET isotherm for multilayer adsorption, comparison between BET and HJr methods, the Frenkel-Halsey-Hill equation (FHH), the Dubinin-Radushkevich equation (D-R), Kiselev's equation Other methods for determining surface area - Langmuir trough, Gravimetric method, the Rayleigh interferometer Determination of pore size distribution by gas adsorption - the Kelvin equation On-line particle analysis - Brinkmann analyser, Climet particle counting systems, Flowvision, Hiac/Royco (Pacific Scientific) particle counters, Horiba particle size analysers, the Insitic particle counter, Kane May particle size analysers, Kratel Partascope, Lasentec, Talbot optical-electronic method, the Erdco acoustical counter, the Coulter on-line monitor screening - the Cyclosensor, non-Newtonian rheological properties Appendix 1 Equipment and suppliers, manufacturers' and suppliers' addresses
1,592 citations
TL;DR: In this article, it was shown that for a colloidal particle of any shape the mobility is independent of the dielectric properties of the particle and the electrostatic boundary conditions on the particle surface.
Abstract: The equations which govern the ion distributions and velocities, the electrostatic potential and the hydrodynamic flow field around a solid colloidal particle in an applied electric field are reexamined. By using the linearity of the equations which determine the electrophoretic mobility, we show that for a colloidal particle of any shape the mobility is independent of the dielectric properties of the particle and the electrostatic boundary conditions on the particle surface. The mobility depends only on the particle size and shape, the properties of the electrolyte solution in which it is suspended, and the charge inside, or electrostatic potential on, the hydrodynamic shear plane in the absence of an applied field or any macroscopic motion.New expressions for the forces acting in the particle are derived and a novel substitution is developed which leads to a significant decoupling of the governing equations. These analytic developments allow for the construction of a rapid, robust numerical scheme for the solution of the governing equations which we have applied to the case of a spherical colloidal particle in a general electrolyte solution. We describe a computer program for the conversion of mobility measurements to zeta potential for a spherical colloidal particle which is far more flexible than the Wiersema graphs which have traditionally been used for the interpretation of mobility data. Furthermore it is free of the high zeta potential convergence difficulties which limited Wiersema's calculations to moderate values of ζ. Some sample computations in typical 1:1 and 2:1 electrolytes are exhibited which illustrate the existence of a maximum in the mobility at high zeta potentials. The physical explanation of this effect is given. The importance of the mobility maximum in testing the validity of the governing equations of electrophoresis and its implications for the colloid chemist's picture of the Stern layer are briefly discussed.
1,563 citations