Particle Sizing

Iwao Teraoka Polytechnic University

Outline of the Tutorial

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Overview

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Static light scattering

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Dynamic light scattering

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Dynamic structure factor and diffusion

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Particle sizing by DLS

Outline of Overview

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Methods of particle sizing

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Laser diffraction

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Hydrodynamic chromatography

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Electrical-sensing zone

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Single-particle optical sensing

Particle Size Distribution: Where Is It Measured?

Powders (wheat, starch, cement, drugs, detergents, etc.) Suspensions (milk, paints, inks, blood, etc.) Gels (yogurt, mayonnaise, pastes, etc.) Aerosols (spray, smoke, Anthrax, etc.) analytical online monitoring in process control

Instrument Manufacturers

Brookhaven Instruments (NY) Coulter (FL) — Beckman-Coulter (CA) Horiba (Japan) Malvern (UK) NiComp (CA) Otsuka (Japan) Polymer Laboratories (UK) ...

Methods of Particle Sizing method LD (FD) SPOS DLS (QELS, PCS) HDC principle diffraction Mie scattering light blockage diffusion fluid dynamics manufacturers Coulter, Horiba, Malvern NiComp Coulter, BIC, Malvern, NiComp PL ESZ electric current Coulter Other methods include optical microscopy, sieving, and sedimentation.

Range of Measurement OM: optical microscopy SPOS: single particle optical sensing LD: laser diffraction FD: Fraunhofer diffraction ESZ: electrical-sensing zone DLS: dynamic light scattering QELS: quasi-elastic light scattering PCS: photon correlation spectroscopy HDC: hydrodynamic chromatography

Particle Sizing: Assumption Assume that the solute consists of independently moving spheres of different radii.

Hydrodynamic Chromatography (HDC) column packed with solid spheres flow velocity in a narrow channel larger particles smaller particles Larger particles flow ahead of smaller particles.

HDC in Size Exclusion Chromatography

HDC mode

Single-Particle Optical Sensing (SPOS) SPOS detects the shadow. Obviously, it cannot measure particles smaller than ~1 µm. To extend the range to less than 1 µm, SPOS has an additional detector for detecting light diffracted (scattered) by the smaller particles.

Electro-Zone Sensing (Coulter Principle) As a particle blocks the orifice, the conductivity drops temporarily.

Laser Diffraction (Fraunhofer Diffraction) Angular dependence of the scattering intensity (diffraction pattern) is different for particles of different sizes.