Droplet size measurement light scattering

Elastic and inelastic light scattering are nowadays widely used techniques for the characterization of fluids. In particular, these techniques have been extensively and successfully used with microemulsion systems to obtain information about droplet sizes. Surface light scattering is a less common technique but has been used with microemulsion interfaces, in particular to measure the ultralow interfacial tensions found in these systems. In this chapter we discuss these aspects, first recalling the theoretical background and illustrating the potential of the techniques with experimental results. 

Figure 7.17 Influence of i-carrageenan on the state of flocculation of BSA-stabilized emulsions (20 vol% oil, 1.7 vt% protein. pH = 6, ionic strength = 0.005 M) stored at 25 °C for 40 hours. The average droplet size measured by static light scattering (Malvern Mastersizer), d32, is plotted against the polysaccharide concentration ch added to the freshly made emulsion. Reproduced from Dickinson and Pawlowsky (1997) with permission.

Particle size distribution (oil droplets) using a light scattering technique was measured on a Leeds and Northrop Microtrak particle size analyzer as described by Weiss and Frock (18). Replicate samples of the encapsulated products were dissolved in water. The beta-cyclodextrin sample was only partially soluble therefore, the insolubles were allowed to separate out before removing the supernatent for evaluation. 

A third possibility is to follow the dynamics of droplets. With dynamic light scattering, the Doppler shift relative to the frequency of the incident light in the scattered light is measured. This Doppler shift comes from the Brownian motion of the droplets. Since larger droplets show slower Brownian motion, one can obtain information on the droplet size distribution. 

Other important characterization techniques include electrophoresis measurements of droplets [11, 12] (see Section XIV-3C), infrared absorption of the constituent species [13], and light or x-ray scattering. NMR self-diffusion measurements can be used to determine droplet sizes in W/0 emulsions [14]. 

An experimental method based on the theories for rainbow phenomena has been applied to the measurement of droplet size and velocity and to the detection of non-sphericity.[7] In this method, a comparison between two droplet diameters is deduced from two different optical interference patterns observed in a rainbow that is created by a droplet scattering laser light. Once a rainbow pattern is... 

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