Flow ultramicroscope

ISPA 800 series characterizes the size and shape of 5 pm to 10 mm particles by measuring the projected areas of the particles in a strobed image. The unit, manufactured by Greenfield, can process 15 images per second and can analyze particles moving at 30 m sec.  

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The second method for obtaining the rate constant of flocculation is by direct particle counting as a function of time. For this purpose optical microscopy or image analysis may be used, provided the particle size is within the resolution limit of the microscope. Alternatively, the particle number may be determined using electronic devices such as a Coulter counter or a flow ultramicroscope. 

Figure 6.13. In the flow ultramicroscope, fineparticles welling up the centre of the column scintillate as they pass through the laser beam and are counted, a) Sketch of the ultramicroscope system, b) Comparison of results from the flow ultramicroscope to image analysis data for a suspension of latex spheres.

If dilution and counting were fully automated, the flow ultramicroscope might well provide rapid, on-line particle size analysis. To the author s knowledge, commercial units are not available, and construction of a prototype is admittedly difficult. 

Grimley (G10, Gil) used an ultramicroscope technique to determine the velocities of colloidal particles suspended in a falling film of tap water. It was assumed that the particles moved with the local liquid velocity, so that, by observing the velocities of particles at different distances from the wall, a complete velocity profile could be obtained. These results indicated that the velocity did not follow the semiparabolic pattern predicted by Eq. (11) instead, the maximum velocity occurred a short distance below the free surface, while nearer the wall the experimental results were lower than those given by Eq. (11). It was found, however, that the velocity profile approached the theoretical shape when surface-active material was added and the waves were damped out, and, in the light of later results, it seems probable that the discrepancies in the presence of wavy flow are due to the inclusion of the fluctuating wavy velocities near the free surface. 

In an ingenious ultramicroscopic study of the components of turbulent flow near a pipe wall, Page and Townend (19) showed that a film of liquid at the wall possesses a small degree of Jerky, laminar flow, while the v - component normal to the interface fails to very small values. To account for the exponential variation of k with D, King (lib) assumed that v might be proportional to a small power, say the cube, of the distance d (Fig. i) ... 

To determine the concentration of the dispersed particles, one often replaces ordinary ultramicroscope with fl o w u ltr am icroscope designed by B. Derjaguin and G. Vlasenko [42], In the flowing suspension this device registers the number of particles that travel per unit time across the microscope field, allowing one to rapidly determine the particle concentration in sols. The use of optical electronic devices for the measurement of intensity of light scattered by individual particles makes it possible for one to obtain also the particle size distribution curves. 

The electroosmotic flow rate can then be calculated hy Q = Mave c- Although it is possible to directly measure the electroosmotic mobility using the ultramicroscope technique [1],... 

The electro-osmotic flow rate can then be calculated by Q = Mave c- Although it is possible to directly measure the electro-osmotic mobility using the ultramicroscope technique [1], however, it is common to measure it by means of measuring the average electro-osmotic velocity. Once the average velocity is obtained, the electro-osmotic mobility can be easily determined by /jLqq =... 

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