Arial 10 pt, right (odd) or left (even): Particulate Systems Analysis 2008, Stratford-upon-Avon, UK
037 Nanoparticle Measurement by Spectroscopic Mie Scattering
Rick Trutna, Maozi Liu, Danielle Chamberlin, Judith Hadley
Agilent Technologies, 1400 Fountaingrove Parkway, Santa Rosa, CA 95403
judith_hadley@agilent.com
ABSTRACT:
In this paper we present a spectroscopic technique for measuring particle size. The technique
utilizes a UV-Visible spectrophotometer to measure the attenuation spectrum of a particle dispersion
due to scattering. Using the Mie scattering theory, we compute the particle size distribution and
particle concentration that best matches the measured scattering spectrum. While the operating range
is material dependent, we have found that the instrument can measure particles sizes from 10 nm to
15 microns. The technique involves minimal sample preparation and clean up, and is fast. A
measurement time of less than 10 seconds allows measurement of samples where dispersion stability
is an issue or when the particles are dense and the sedimentation rate make traditional measurement
techniques challenging. Since the technique does not rely on observing the Brownian motion of
particles, the samples may be stirred or flowed during the measurement via the use of a stir bar
accessory or utilizing flow through cells. An additional advantage of the technique is the ability to
measure highly concentrated colloids at or near process concentrations with no dilution.
Fast measurement time enables the study of samples changing over short timescales. This
information can be critical in reaction kinetic studies and aggregation studies in biological systems. As
well the fast measurement time has advantages for measurement of inorganic systems. For example,
the dispersion of metal powders in water has been little studied due to two major problems: the
complex colloidal behavior in which not only oxidation and hydrolysis but also dissolution occurs,
depending on pH and temperature, and the density of most metals that promotes fast settling. Nickel
powders have a high density, so that electrostatic repulsion is not sufficient itself to overcome the
tendency to settle. With further complications due to its magnetic properties, surface modification
techniques utilizing steric stabilization are required to prevent agglomeration. Obtaining accurate
measurements the particle size of Ni is challenging in this environment of dispersion instability. The
fast measurement times of our UV-Visible particle sizing technique facilitate measurement of such
unstable systems.
We report experimental results comparing particle size measurements via this technique to SEM
image analysis demonstrating the accuracy of the measurement. We also present experimental
results demonstrating the capability of this technique to accurately measure the concentrations of
populations in difficult bi- or multi-modal particle size distributions. Figures 1 demonstrates the
resolution capability of the UV-Visible particle sizing instrument with a sample of equal concentrations
of 200nm and 300nm polystyrene latex. Such resolution has also been demonstrated for metal
nanoparticles as well - figure 2 shows the particle size distribution of an 80nm and a 150nm gold
standard dispersions mixed in a 1:3 ratio. Figure 3 demonstrates the sensitivity with the detection of 5
% v/v 100 nm polystyrene latex particles in a background of 95% v/v 3 µm particles. We believe this
combination of fast measurement time, high resolution, and ease of sample preparation offers distinct
advantages over existing techniques and enables new measurements.
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Arial 10 pt, right (odd) or left (even): Particulate Systems Analysis 2005, Stratford-upon-Avon, UK
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314
100
0.0020
213
0.015
Conc. (% v/v)
0.0016
0.0014
0.0012
0.0010
0.0008
0.0006
80
60
0.010
40
0.005
20
0.0004
0.0002
0.0000
10.0
98
0.000
31.6
100.0
316.2
1000.0
nm
3162.3
10000.0
Figure 1: Measurement of particle size
distribution of a mixture equal concentrations 200
and 300nm nominal diameter polystyrene latex
nanoparticles.
0
10
100
1000
Particle size (nm)
10000
Figure 2: Measurement of particle size distribution
of a mixture of 5% v/v 100nm and 95% v/v 3um
polystyrene latex particles. Blue line: absolute
concentration, red line: cumulative concentration.
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Cumulative %
Conc. (% v/v)
0.0018