Dynamic light scattering
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Transcript of 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