Nanoparticle Analysis: Dynamic Light Scattering for ...€¦ · Other Light Scattering Techniques...

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© 2011 HORIBA, Ltd. All rights reserved. Nanoparticle Analysis: Dynamic Light Scattering for Particle Size Determination Jeffrey Bodycomb, Ph.D. HORIBA Scientific www.horiba.com/us/particle

Transcript of Nanoparticle Analysis: Dynamic Light Scattering for ...€¦ · Other Light Scattering Techniques...

Page 1: Nanoparticle Analysis: Dynamic Light Scattering for ...€¦ · Other Light Scattering Techniques Static Light Scattering: over a duration of ~1 second. Used for determining particle

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Nanoparticle Analysis: Dynamic Light Scattering for Particle Size Determination

Jeffrey Bodycomb, Ph.D.HORIBA Scientific

www.horiba.com/us/particle

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What is Dynamic Light Scattering?

Dynamic light scattering refers to measurement and interpretation of light scattering data on a microsecond time scale.Dynamic light scattering can be used to

determine Particle/molecular sizeSize distributionRelaxations in complex fluids

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Other Light Scattering Techniques

Static Light Scattering: over a duration of ~1 second. Used for determining particle size (diameters greater than 10 nm), polymer molecular weight, 2nd virial coefficient, Rg.

Electrophoretic Light Scattering: use Doppler shift in scattered light to probe motion of particles due to an applied electric field. Used for determining electrophoretic mobility, zeta potential.

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Particle Diameter (m)0.01 0.1 1 10 100 1000

Colloidal

Suspensions and Slurries

DLS – SZ-100

Electron Microscope

Powders

Fine Coarse

Microscopy PSA300

Laser Diffraction – LA-950

Acoustic Spectroscopy – DT-1201 and DT-300(Zeta)

Electrozone Sensing

Disc-Centrifuge (CPS)

Light Obscuration

0.001

Macromolecules

Nano-Metric

Met

hods

Met

hods

App

sA

pps

Size

sSi

zes

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Particles in suspension undergo Brownian motion due to solventmolecule bombardment in random thermal motion.

Brownian MotionRandomRelated to SizeRelated to viscosityRelated to temperature

Brownian Motion

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Particles

Zeta potential

Backscatter (173°)(High conc.)

90° for size and MW, A2

Laser

Modulator

PDFor T%532nm, 10mW

Attenuator

Attenuator

Particles movingdue to Brownianmotion

DLS Optics

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DLS signalRandom motion of particles leads to random

fluctuations in signal (due to changing constructive/destructive interference of scattered light.

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Correlation Function

Random fluctuations are interpreted in terms of the autocorrelation function (ACF).

)()(

)()()( 0

tItI

dttItIC

T

)2exp(1)( C

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Gamma to Size

2qDm 2sin4

nq

m

Bh DT

TkD)(3

decay constantDm diffusion coefficientq scattering vectorn refractive index wavelength scattering angleDh hydrodynamic diameter viscositykB Boltzman’s constant

Note effect of temperature!

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What is Hydrodynamic Size?

DLS gives the diameter of a sphere that moves (diffuses) the same way as your sample.

Dh DhDh

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Hydrodynamic Size The instrument reports the size of sphere that

moves (diffuses) like your particle. This size will include any stabilizers bound to the

molecule (even if they are not seen by TEM).

SEM (above) and TEM (below) images for RM 8011

Technique Size nmAtomic Force Microscopy 8.5 ± 0.3Scanning Electron Microscopy 9.9 ± 0.1Transmission Electron Microscopy 8.9 ± 0.1Dynamic Light Scattering 13.5 ± 0.1

Gold Colloids

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Polystyrene Latex Sample

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Polydisperse Sample Cumulants

For a mixture of sizes, the autocorrelation function can be interpreted in terms of cumulants. This is the most robust method of analyzing DLS data.

!22exp1)( 2C

2qDm

m

Bhz DT

TkD)(3,

22

sityPolydisper

“z-average size”

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SiO2

0.077479.8Avg.0.039487.740.077478.830.066479.520.127473.21

Polydispersity Index

Z-average Diameter (nm)

Run

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Polydisperse Sample (ILT) A more general relationship can be given between the

autocorrelation function and the size distribution. Let each size have a relation constant . The scattering from each population is then given by S(). Now we have an integral equation. Solving for S() gives us size distribution.

dSg )exp()()()1(

2)1( )(1)( gC

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Bimodal SampleNominal 20 nm and 500 nm latex run

individually

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Bimodal Sample

Mixed sample (in black)

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Dynamic Light Scattering Practical Tips

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Dust

Dust: large, rare particles in the sampleGenerally not really part of the sampleSince they are rare cannot get good

statistics

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Filter to removedust. If particles are too large (D >50 nm for 0.1 m filter), at least filter diluent.

Filters available in sizes 20nm to 2m

We can also centrifuge the sample and extract the supernatant.

Filtering

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The Natural limit for Dynamic Light Scattering: Gravitational Settling

Gravitational Settling occurs at about 1-3m

Particle Diameter(m)

Movement due toBrownian Motion

Movement due toGravitational Settling

0.01 2.36 >> 0.0050.25 1.49 > 0.03460.50 1.052 > 0.13841.0 0.745 ~ 0.5542.5 0.334 < 13.84

10.0 0.236 << 55.4

Settling and DLS

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Why DLS?

Non-invasive measurementRequires only small quantities of

sampleGood for detecting trace amounts of

aggregateGood technique for macro-molecular

sizing

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New Nanoparticle Analyzer

Single compact unit that performs size, zeta potential, and molecular weight measurements.

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Q&A

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Jeff Bodycomb, Ph.D. P: 866-562-4698E: [email protected]