Particle size measurement light scattering methods

Salt, K. Noble, C. A. Prather, K. A. Aerodynamic particle sizing versus light scattering intensity measurement as methods for real-time particle sizing coupled with time-of-flight mass spectrometry. Anal. Chem. 1996, 68, 230-234. 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

In contrast to osmotic pressure, light-scattering measurements become easier as the particle size increases. For spherical particles the upper limit of applicability of the Debye equation is a particle diameter of c. A/20 (i.e. 20-25 nm for A0 600 nm or Awater 450 nm or a relative molecular mass of the order of 10 ). For asymmetric particles this upper limit is lower. However, by modification of the theory, much larger particles can also be studied by light scattering methods. For polydispersed systems a mass-average relative molecular mass is given. 

The preservation of particle character and size throughout polymerization itself is very hard to determine. The size of the final polymer particles is easily determined by light scattering or microscopic methods since the dispersions can be diluted without changing the particle size. Measurements of the emulsion droplets in concentrated media on the other hand are a very difficult task and have already been discussed above. 

This is based on the principle of light scattering of particles as a function of their hydrodynamic radius. Commonly used, as it requires a small sample size and is a rapid method for particle size measurement. It can be used to measure particles varying in size from 0.001 to 100pm. 

Bernhard, R. (1981) Rapid Measurement of Particle Size Distributions by use of Light Scattering Methods, Paper presented at PARTEC Nuremberg May 6-9 (POLYTEC). 

As already indicated in Chapter 7, the introduction of laser technology has already had a major impact on light-scattering methods. These have found particular application in the development of new methods of particle sizing, and several instruments are now available commercially which arc designed for the automatic determination of particle size distributions. These methods are being developed steadily, especially in terms of the associated computer software needed for the rapid analysis of experimental data. In particular, while the measurement of the particle size in monodisperse systems is well established, the mathematical analysis for polydisperse systems and for non-spherical particles presents problems which are not yet fully solved. 

Prior to the 1970s, methods such as light scattering and surface area measurements were used to obtain average particle size of colloidal silica. Both of these methods assume that the particles are spheres. Light scattering... 

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