Particle Sizing

Understanding the particle size distribution of nanomaterials can be critical in terms of the material properties and potential applications. We offer a range of techniques, including dynamic light scattering (DLS) and laser particle tracking, to characterise the particle size of a range of sample types to enable you to develop your material applications.

Dynamic Light Scattering (DLS)

Particles which are smaller than the wavelength of the incident light (typically <250nm for UV-visible light) can scatter the light (Rayleigh scattering). In suspension, Brownian motion of the particles will cause the scattering to change with respect to time causing fluctuations in the constructive and destructive interference occurring. The resultant fluctuation in scattered light can be used to infer the motion of the particles which in turn can be used to infer the size of the particles.

In addition to this, for study of nanoparticles we use a Mastersizer particle analyser which employs optics to enable analysis of particles up to 3.5mm in diameter using the same light scattering approach.

Laser Diffraction

This technique works along a similar principle to DLS but rather than using fluctuation in the intensity of scattered light to infer motion and therefore size, laser diffraction analyses the intensity of the scattered light as a function of the scattering angle.

Since there is a direct relationship between the intensity of the scattered light/angle and particle size (Mie theory) this allows the particle size to be determined.

Laser Particle Tracking

Similar to DLS, laser particle tracking uses the scattering of small particles by light to determine motion and therefore particle size. With this technique, however, the particles are visualised directly via the scattered light using a microscope, tracking software measures particle movement and the Stokes Einstein equation is then applied to determine the hydrodynamic diameter of the particles.

Zeta Potential

Particles with a charge (e.g. silver ions) will attract oppositely charged ions which form a layer around the particle. Around this layer will be another, more diffuse, layer of oppositely charged ions, i.e. the same charge as the particle, termed the Stern layer.

As the particle moves so the two charged layers move with it forming a hydrodynamic boundary across which occurs a potential difference, the zeta potential.

If the zeta potential within a system is sufficient (either positive or negative) then the repulsion between the particles will be sufficient to keep the particles in suspension thus avoiding aggregation.

The stability of a colloid can therefore be assessed by measuring the zeta potential of a suspension. By applying an electric field across a suspension and measuring the change in particle movement (electrophoretic mobility) via changes in the scattering of incident light (c.f. DLS), the zeta potential may be determined.

Our nanomaterial testing can be applied to a range of colloidal nanomaterials (e.g. silver, gold, carbon). In addition, biomolecules can be assessed to determine protein aggregation or characterisation of vesicles.

Samples should be capable of forming stable liquid colloids / suspension and in order to scatter light should be ≤3.5mm in diameter. Minimum sample volume is typically of the order of 1ml, although less may be required.