Droplet size measurement microscopy

Particle Size Measurement. The best way to evaluate an emulsion s stability is probably to measure its particle size distribution. A number of methods are available for droplet size determination (see Sec. VIII.A). Optical microscopy, although a time-consuming technique, is a direct way of measuring droplets larger than 1 pm. Nowadays, laser lightscattering, diffraction, and transmission methods are becoming popular for routine determination of particle size [151, 152],... 

There is a variety of methods for determining the droplet size distribution. One can directly measure the size by using microscopy. When the droplets are larger than 1 pm, this can be done by optical microscopy for smaller droplets this is not possible, and electron microscopy may be used. 

To measure the droplet size distribution of the resulting multiple emulsion (with diameters >5 pm), optical microscopy combined with image analysis can be used. An alternative method to measure droplet size distribution is to use light diffraction and then to apply Fraunhofer s diflraction theory. Details of this method are provided in Chapter 19, but basically a laser beam that has been enlarged and... 

Using various physicochemical techniques such as high resolution NMR, viscosity, and electrical resistivity measurements, Chan and Shah [26] proposed that the middle-phase microemulsion in three-phase systems at or near optimal salinity is a water-external microemulsion of spherical droplets of oil. Extended studies to characterize the middle-phase microemulsions by several techniques including freeze-fracture electron microscopy revealed the structure to be a water-external microemulsion [26]. The droplet size in the middle-phase microemulsion decreases with increasing salinity. A freeze-fracture electron micrograph of a middle-phase microemulsion is shown in Fig. 8. It clearly indicates that the discrete spherical structure of the oil droplets in a continuous aqueous phase is consistent with the mechanism proposed in Fig. 7. This system was extensively studied by Reed and coworkers [20-22]. 

Electron microscopy provides an image of the particles to be measured. In particular, SEM is used for vacuum dried nanoparticles that are coated with a conductive carbon-gold layer for analysis and TEM is used to determine the size, shape, and inner core structure of the particles. TEM in combination with freeze-fracture procedures differentiates between nanocapsules, nanospheres, and emulsion droplets. AFM is an advanced microscopic technique and its images can be obtained in aqueous medium. AFM images, nowadays are a powerful support for the investigation of nanoparticles in biological media. 

In the LASC-catalysed reactions, the formation of stable emulsions seemed to be essential for the efficient catalysis. We thus imdertook the observation of the emulsions by means of several tools. Optical microscopic observations of the emulsions revealed the formation of spherical emulsion droplets in water (Figure 13.1). The average size of the droplets formed from 3 in the presence of benzaldehyde in water was measured by dynamic light scattering, and proved to be ca. 1.1 pm in diameter. The shape and size of the emulsion droplets were also confirmed by transmission electron microscopy and atomic force microscopy. 

---