Particle Sizing

1
Particle Sizing

• Iwao Teraoka
• Polytechnic University

2
Outline of the Tutorial

• Overview
• Static light scattering
• Dynamic light scattering
• Dynamic structure factor and diffusion
• Particle sizing by DLS

3
Outline of Overview

• Methods of particle sizing
• Laser diffraction
• Hydrodynamic chromatography
• Electrical-sensing zone
• Single-particle optical sensing

4
Particle Size DistributionWhere 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
5
Instrument Manufacturers
Brookhaven Instruments (NY) Coulter (FL)
Beckman-Coulter (CA) Horiba (Japan) Malvern
(UK) NiComp (CA) Otsuka (Japan) Polymer
Laboratories (UK) ...
6
Methods of Particle Sizing
Other methods include optical microscopy,
sieving, and sedimentation.
7
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
8
Particle Sizing Assumption
Assume that the solute consists of independently
moving spheres of different radii.
9
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.
10
HDC in Size Exclusion Chromatography
HDC mode
11
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.
12
Electro-Zone Sensing (Coulter Principle)
As a particle blocks the orifice, the
conductivity drops temporarily.
13
Laser Diffraction (Fraunhofer Diffraction)
Angular dependence of the scattering intensity
(diffraction pattern) is different for particles
of different sizes.