dynamic light scattering

Dynamic Light Scatteringand other particle sizing techniques

Ed Mansfield

Introduction

• The nanoscale• Dynamic Light Scattering• Types of measurement• Data analysis• Comparative techniques

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A ruler

Conventional microscopy

Electron microscopyDynamic Light Scattering

Particle Tracking techniques

nm

X-ray/neutron techniques

µm mmpm

DLS – how it works

Laser Detector

AutocorrelationSize distribution

DLS theory• Measures scattering of particles undergoing

Brownian motion• Diffusion coefficient is calculated based on

scattering and an autocorrelation function• Calculates a particle size from the diffusion

coefficient from the Stokes-Einstein equation

Types of measurement

• Particle size• Calculates an intensity based particle size (z average)• Determines a PDI

• Zeta potential• Measures colloidal stability

• Static Light scattering• Molecular weight

Creating an SOP• Things needed before a measurement can be

taken:• Refractive index of particle/polymer• If coloured, the absorption is needed• Refractive index and viscosity of solvent

• Follow onscreen instructions to make SOP• Repeat readings• Load SOP and start

Sample preparation

Raw data

Data analysis – the good

Data analysis – the bad

Data analysis – the ugly

Data analysis – the ugly

“Expert advice”

Good data

Bad data

Expert advice isn’t 100%

Comparative techniquesDLS Particle Tracking Transmission Electron

microscopy

Size range: 0.3nm to 10µm Size range: 10nm to 2 µmSize range (depending on

resolution from sample): 1 nm up to a few µm

Size, polydispersity, and zeta potential

Size, diffusion coefficient, and concentration Size and morphology

Biased towards larger particles Detects particles of all sizes (within the size range)

Detects particles of all sizes

Quick and easy to run samples Easy to use, but more labour intensive

Can be time consuming and expensive

Highly reproducible data (assuming sample is good and

without contamination)

Highly reproducible data, but requires more runs, as only a

small volume of sample is measured

Requires lots of images to gain an accurate representation of

particles

Data produced can be misleading

Data produced is dependent on operator settings

Generates images. Needs specialist expertees to gain

statistical data

High start-up cost, low running cost

High start-up cost, low running cost

High start-up cost and running cost

Summary

• Good technique for gaining a particle size/dispersity/zeta potential

• High throughput and easy to use• Can measure thermoresponsive systems effectively• Biased towards larger particles• Struggles with polydispersed samples• Data analysis and quality control can be complicated• Not absolute, and should be used in conjunction to

other techniques

Thanks for listening