Particle Size Distribution

 Malvern Autosizer

Scope and Field of Application

We can determine the size of particles in the 5 to 5000 nanometre range (0.005 to 5 microns) using photon correlation spectroscopy (PCS). This technique is also known as quasi-electric light scattering (QELS) and dynamic light scattering (DLS).

One characteristic of particles in this size range is that they are in constant random thermal or Brownian motion. This motion causes the intensity of light scattered by the particles to vary with time. Large particles move more slowly than small particles and consequently the rate of fluctuation of light scattered by the large particles is also slower. Photon correlation spectroscopy measures the rate of change of the light fluctuations and uses this information to calculate the size distribution of the particles.

This work is not carried out to any international standard, we use our own in-house method.

Summary of Method

We carry out the determination using a Malvern AutoSizer Model Hi-C fitted with a 64 channel 7032 correlator. The sample is diluted, if necessary, to give between 2 and 10% solids. In principle the method requires no calibration since the performance depends on fixed physical quantities such as temperature and the wavelength of the incident light. In practice however we check that the system is operating correctly using standard latex samples with a narrow size distribution.

Sample Requirements

Currently our experience is limited to measuring the size distribution of water borne latices of the type used to make emulsion paints. In fact the method is applicable to a stable dispersion of any homogenous material in water or organic solvents provided the particles are within the 5 to 1,000 nanometre size range.

The method is not suitable for samples that contain material outside this size range even if no information is required about the out-of-range particles. It is also unsuitable for dispersions within the size range if the particles are a mixture of different materials.

We require no more than 100 g of sample.

Accreditation

Although PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS), we are not accredited to carry out this particular test.

 

 

Please contact Peter Collins for further details.

 

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