Light microscopy emulsions

Jenkins EC. Wire-loop application of liquid emulsion to slides for autoradiography in light microscopy. Stain Technol 1972 47 23-26. 

Because of this importance, different techniques have been developed to characterize the droplet size distribution in emulsions, each with its own pros and cons. Light microscopy, for example, is qualitative and only suited for particles larger than about 1 )im. When using electron microscopy, correct sample preparation is crucial to the examination and interpretation of the dispersions. The Coulter method is an indirect method which detects a... 

To avoid adverse effects on injection it is important that the particle size of the emulsions is small and remains so on storage. After storage of Intralipid for two years at 4°C, more than 99% of the particles visible by light microscopy had a diameter of less than 1 fim that is, there was practically no change in mean diameter. 

It has been observed by polarized light microscopy that some emulsion droplets (diameter about 5 /an), containing a triglyceride oil that can partly crystallize at room temperature, have crystalline fat in their outer layer. This has been ascribed to the cooling of the droplets occurring from the outside, so that crystallization would start there. Is this a reasonable explanation ... 

A few distributions of VCM suspensions in water viewed by light microscopy into specially designed pressure cells appear in the literature (23,24), but no analyses of droplet size distribution under different conditions of reactor agitation or polymeric additive addition have been reported. A technique for fixing VCM emulsions by osmium tetroxide (25) may prove useful to study the VCM/water system in greater detail. Mersmann and Grossmann (26) have studied the dispersion of liquids in non-miscible two-phase systems, which include chlorinated liquids such as carbon tetrachloride in water. The influence of stirrer type and speed on the development of an equilibrium droplet size distribution is discussed. Different empirical relationships to calculate the Sauter mean diameter of droplet distributions from reactor operating parameters are also reviewed. 

Microscopy. Particle size, shape and structure of emulsion droplets can be visualized by various microscope techniques, such as phase contrast light microscopy, confocal scanning light microscopy (CSLM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray microtomography (XRT), atomic force microscopy (AFM) and imaging techniques. 

The detection of Hquid crystal is based primarily on anisotropic optical properties. This means that a sample of this phase looks radiant when viewed against a light source placed between crossed polarizers. An isotropic solution is black under such conditions (Fig. 12). Optical microscopy may also detect the Hquid crystal in an emulsion. The Hquid crystal is conspicuous from its radiance in polarized light (Fig. 13). The stmcture of the Hquid crystalline phase is also most easily identified by optical microscopy. Lamellar Hquid crystals have a pattern of oil streaks and Maltese crosses (Fig. 14a), whereas ones with hexagonal arrays of cylinders give a different optical pattern (Fig. 14b). 

Figure 7.22 Microstructure of acidified mixed emulsions (20 vol% oil, 0.5 wt% sodium caseinate) containing different concentrations of dextran sulfate (DS). Samples were prepared at pH = 6 in 20 mM imidazole buffer and acidified to pH = 2 by addition of HCl. Emulsions were diluted 1 10 in 20 mM imidazole buffer before visualization by differential interference contrast microscopy (A) no added DS (B) 0.1 wt% DS (C) 0.5 wt% DS (D) 1 wt% DS. Particle-size distributions of the diluted emulsions determined by light-scattering (Mastersizer) are superimposed on the micrographs, with horizontal axial labels indicating the particle diameter (in pm). Reproduced with permission from Jourdain et al. (2008).

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