Droplet microscopic visualization

A variety of assays have been developed to quantify phagocytic activity. These include direct microscopic visualization (2,3), spectrophotometric evaluation of phagocytized paraffin droplets containing dye (4), scintillation counting of radiolabeled bacteria (5), fluorometric (6), and flow cytometric analysis of fluorescent particles (7-13). The flow cytometric assay offers the advantage of rapid analysis of thousands of cells and quantification of the internalized particle density for each analyzed cell. The assay may be performed with purified leukocyte preparations (7-13) or anficoagulated whole blood (14,15). 

Figure 13.21 Microscopic visualization of the droplet formation at dispersed phase velocities below (left) and above (right)...

In the past decade microscopic detection of specific types of coalescence within double-emulsion droplets has contributed to a better understanding of these mechanisms in order to control their occurrence. Three types of coalescence events have been identified in double-emulsion systems. These include coalescence between contacting inner droplets (internal coalescence), coalescence of interior droplets with the outer continuous phase (external coalescence), and coalescence between contacting two-phase emulsion globules. Direct evidence of each type of coalescence has been collected for double emulsions with microscopic visualization. The type and concentrations of surfactants in each phase of the water/oil/water double emulsions are critical in controlling the occurrence and type of coalescence (Ficheux et al., 1998 Villa et al., 2003 Hou and Papadopoulos, 1996 Hou and Papadopoulos, 1997 Pays et al., 2001). 

Static method, using a Kriiss G-1 optical microscope equipped with a goniometer (Fig. 2b) [10]. Approximately 100 mg of the powder is compressed into a pellet at a pressure of 1000 MPa. Subsequently a mercury droplet of 2-6 pi is placed on the pellet and a goniometer in the ocular of the microscope is then used to visually determine the specific contact angle (so-called static contact angle). 

A Nikon optical microscope was used to observe states of flocculation of large emulsion droplets. The emulsion samples were regularly viewed with the microscope using the Normarski differential interference contrast technique.16 Creaming behaviour was examined by visually measuring the height (thickness) of cream and serum layers in emulsions stored at 22°C at regular time intervals. 

Milk is heterogeneous, consisting of a continuous fluid phase and fat droplets which can be visualized microscopically. It is a heterogeneous mixture of liquids since its contents are both visualizable and variable in composition. 

Obtained by a visual estimation of lipid droplets in five microscopic fields of heart cells in culture under an inverted phase contrast microscrope (10 x 40). Range 0 to 4. 

The model system essentially consists of small fluorescent beads. A large variety of such beads is commercially available. Their size, surface properties, and fluorescence spectra can be chosen within wide limits. The beads are deposited on coated electron microscopic grids in the form of small drops. After drying, individual droplets are first visualized by confocal fluorescence microscopy and subsequently by standard transmission electron microscopy. Thus, the model system permits one to compare directly confocal with electron microscopic results. This is demonstrated in Fig. 1 (see color plate). Also, the size and average area density of the beads can be matched to those of the NPC. The model system is also well suited for optimizing imaging conditions and quantitating resolution in terms of the point spread function. 

Several methods to obtain and measure pL fluid volumes have been reviewed visual inspection measurement, electric measurement, and optical measurement. Visual inspection measurement captures a droplet image by microscope or stroboscope and measures the size of the droplet in the image to calculate its volume. The minimum volume of droplets can reach 10 pL, with a measurement accuracy of 0.1 pL. Coulometric and impedance methods were introduced as electric measurements, which measure the quantity of electricity or impedance of fluids to calculate the droplet volume. The minimum volume of droplets measurable with these methods is 30 pL, with 1 pL accuracy. Finally, optical measurement, especially the backscatter interferometric method, was introduced. This method measures the difference of light phase to calculate the velocity of a fluid and then calculates the volume. Flow rates from 0.833 to 1.66 nL/s were measured in experiments and the accuracy was 0.127 nL/s. 

Membrane emulsification processes can be directly visualized by microscope as vell as by the use of high-speed cameras. In this case, information can be obtained about droplet disruption [10, 11] and fouling of the membrane. An indirect characterization method is the (inline) measurement of the emulsion characteristics. The emulsion is mainly characterized by its droplet size and droplet size distribution [2]. These infiuence important product characteristics like structure, mouthfeel, color and appearance, texture and viscosity [12, 13]. 

This effect can also be visualized using a microscope. Figure 13.21 shows, on the left, the droplet formation at velocities smaller than the critical velocity, and on the right, the droplet formation at velocities above the critical value. Above the critical velocity, differences in droplet formation on the terrace and droplets of bigger size in the continuous phase are monitored. 

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