Nanoparticles are widely used in many applications. Accurate characterization of nanoparticles is important in research, production and applications in several fields including industry, health, safety and related regulation. At VTT MIKES, the particles can be characterized using two different methods: Dynamic Light Scattering (DLS) and atomic force microscopy (AFM). Our measurement results are traceable to the definition of the metre via MIKES interferometrically traceable metrological atomic force microscope (IT-MAFM).
Both methods have advantages and limitations. DLS is fast method and the results are statistically representative. In DSL measurements, even a small number of large particles can prevent detection of small particles. AFM can be used to measure both size and shape of single particles. The disadvantage of AFM measurements is that only limited number of particles can be measured which leads to poor statistics. Tip sample interaction is important especially when measuring small particles. Also, sample preparation might be challenging.
VTT MIKES have two instruments suitable for nanoparticle measurements.
|Measurands||Size distribution, Zeta potential||Size, shape|
|Measurement range ||0.3 nm – 10 µm||5 nm – 5 µm|
|Measurement uncertainty||2 %||from 1 nm|
Dynamic Light Scattering is used to measure particle and molecule sizes. This technique measures the diffusion of particles moving under Brownian motion, and converts this to size and a size distribution using the Stokes-Einstein relationship. Laser Doppler Micro-electrophoresis is used to measure zeta potential. An electric field is applied to a solution of molecules or a dispersion of particles, which then move with a velocity related to their zeta potential.
Atomic force microscopy (AFM)
An AFM uses a cantilever with a very sharp tip to
scan over a sample surface. As the tip approaches
the surface, the close-range, attractive force between
the surface and the tip cause the cantilever to deflect
towards the surface. However, as the cantilever is
brought even closer to the surface, such that the tip
makes contact with it, increasingly repulsive force takes
over and causes the cantilever to deflect away
from the surface.
In AFM images the topography of a sample surface by
scanning the cantilever over a region of interest. The
raised and lowered features on the sample surface
influence the deflection of the cantilever, which is monitored
by a position-sensitive photo diode (PSPD).
By using a feedback loop to control the height of the
tip above the surface the AFM can generate an accurate topographic map of the surface features.
Our services for nanoparticle characterization
- Nanoparticle size and shape measurements using AFM
- Nanoparticle size distribution in solution using DLS
- Nanoparticle surface charge (Zeta-potential) measurements in solution
- Virpi Korpelainen, Senior Research Scientist, tel.
+358 50 410 5504, email Virpi.Korpelainen(at)vtt.fi
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