Electromagnetic theory, McGraw-Hill, New York (1941) Assumes homogeneous, isotropic and optically linear material Stratton, A.Complete analytical solution of Maxwell’s equations for scattering of electromagnetic radiation from spherical particles.Rayleigh approximation tells us that I α d6 I α 1/λ4 where I = intensity of scattered light d = particle diameter λ = laser wavelength.For small particles (d ≤ λ/10), scattering is isotropic.Interaction of light with matterRayleigh approximation Scattering coefficient varies inversely with the fourth power of the wavelength.This interaction causes a deviation in the light path through an angle calculated using vector analysis.Electromagnetic wave (light) induces oscillations of electrons in a particle.Explained by JW Strutt (Lord Rayleigh).What causes light scattering from (small) particles? How do these fluctuations in scattered light intensity arise?.DLS measures the intensity fluctuations of scattered light arising from Brownian motion.Measure the Brownian motion of particles and calculate size.Nonspherical particles = Rapid Equivalent sphere Slow Hydrodynamic diameter is calculated based on the equivalent sphere with the same diffusion coefficient Affected by surface bound species which slows diffusion Hydrodynamic diameter.Particle diameter + electrical double layer.The diameter measured by DLS correlates to the effective particle movement within a liquid.K) T = temperature (K) η = solvent viscosity (kg/m.Stokes-Einstein Equation dH = hydrodynamic diameter (m) k = Boltzmann constant (J/K=kg Increasing temperature increases Brownian motionīrownian motion Random movement of particles due to bombardment of solvent molecules.Temperature is proportional to diffusion rate.Convection currents induce particle movement that interferes with size determination.Temperature and viscosity must be known.Larger particles diffuse slower than smaller particles.Brownian motion is indirectly proportional to size.Velocity of the Brownian motion is defined by the Translational Diffusion Coefficient (D).Collect scattered light from suspended particles to ….Dynamic Light Scattering ZetaPALS w/ 90Plus particle size analyzer Also equipped w/ BI-FOQELS & Otsuka DLS-700 (Rm CCR230)ĭynamic Light Scattering (DLS) Photon Correlation Spectroscopy (PCS) Quasi-Elastic Light Scattering (QELS)
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