Particle Sizing of nano-dispersions:

Photon Cross Correlation Spectroscopy (PCCS)

Particle sizing of materials from 1 nm to some microns in diameter (the exact values are system dependent) is possible.  Dispersions or emulsions in both water and non-aqueous liquids can be analysed. Dispersions or emulsions in water of non-aqueous liquids can be analysed.

Method
Photon Cross Correlation Spectroscopy (PCCS) is a novel technique allowing for the simultaneous measurement of particle size and stability of opaque suspension or emulsions of nanoparticles in the size range of about 1 nm to some µm. It is a powerful extension of the well established PCS (also called DLS or QELS; it is restricted in use to very dilute systems so that multiple scattering of the laser light is minimised).

The key principle of PCCS using Sympatec's 'NanoPhox' instrument is the use of a 3D cross correlation approach  where multiple scattering is completely suppressed.  This means that the technique can now be used to evaluate more turbid samples than is possible with PCS leading to several advantages

Advantages of PCCS for Particle Sizing

• Relatively high dispersions concentrations can be employed so that count rates are high/ measurement runs are short
• High particle concentrations reduce the sensitivity of this method to extraneous contaminants.
• The amplitude of the cross correlation function (which is produced as part of the analysis) represents the amount of the singly scattered light. This amplitude is extremely sensitive to particle size - an increase in size by a factor of 10 raises the intensity of the scattered light by 10 to the power 6.  So the colloidal stability of dispersions that flocculate or change with time can be followed quite closely.
• It is quite possible to run the instrument in PCS mode without cross correlation so that the two approaches can be compared.
• Small quantities of material only are needed for an analysis since analysis is performed in a cuvette.

The MSG Advantage

• Supporting confirmation of the particle size information can be obtained using :
  • (a) laser diffraction
  • (b) SEM/ TEM coupled with Image Analysis
  • (c) X-ray diffraction (on the dried solid)
  • (d) BET surface area (again on the dried solid).
• Experimentation with various mixers and dispersers (including ultrasonic dispersion) is possible and sometimes recommended.