Ultramicroscopy, flow

The investigation of the kinetics and of the niua-ber of particles in the course of the process was conducted in a special dllatometer which enables one to extract the minimum volume samples (0.03 ml) and requires no compensation for the diminution of the reactive mixture (18). The extracted samples were diluted with the required amount of the emulsifier solution, containing the inhibitor (p-benzoqulnon), were then used to determine the number of particles by flow ultramicroscopy (1j ) and electron microscopy. 

Figure 6 shows that constancy of N, determined by the flow ultramicroscopy method, is achieved at conversion of 20-25%, which would be easily attributed to the stopped formation of a new svirface, since monomer is completely absorbed by particles at this stage, and it is at the expense of this monomer that... 

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 that the particle size is within the resolution hmit of the microscope. Alternatively, the particle number may be determined using electronic devices such as the Coulter counter or flow ultramicroscopy. 

The difference in turbidity owing to the formation of doublets from single particles has been studied by Lichtenbelt, Ras, and Wiersema (234). Also, aggregation has been followed by flow ultramicroscopy (235). 

An instrument developed for the characterization of submicron fineparticles is shown in Figure 6.13. Fineparticles too small to be resolved as images can still be seen in dark-field-illuminated microscope systems by the scintillations of light that they create as they move into the plane of the microscope. Techniques for studying objects in this way are described as ultramicroscopy. The instrument shown in Figure 6.13 exploits ultramicroscopy and the measurement procedure is known as flow ultramicroscopy . In the original system developed by Davidson, Collins and Haller, a suspension stream of latex was made to flow up and through the plane of a dark-field-illuminated microscope and the scintillations created by the presence of the latex fineparticles counted... 

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