Particle Sizing

Iwao Teraoka

Polytechnic University

Outline of the Tutorial

Overview

Static light scattering

Dynamic light scattering

Dynamic structure factor and diffusion

Particle sizing by DLS

Outline of Overview

Methods of particle sizing

Laser diffraction

Hydrodynamic chromatography

Electrical-sensing zone

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.)

analyticalonline 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 principle manufacturers

LD (FD) diffractionMie scattering

Coulter, Horiba,Malvern

SPOS light blockage NiComp

DLS(QELS, PCS)

diffusion Coulter, BIC,Malvern, NiComp

HDC fluid dynamics PL

ESZ electric current Coulter

Other methods include optical microscopy, sieving, and sedimentation.

Range of Measurement

OM: optical microscopySPOS: single particle optical sensingLD: laser diffractionFD: Fraunhofer diffractionESZ: electrical-sensing zone

DLS: dynamic light scatteringQELS: quasi-elastic light scatteringPCS: photon correlation spectroscopyHDC: 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.

photodetectorlight source

fluid

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.