ABSTRACT
An optical video microscopic system and image processing and data extraction and manipulation routines are developed for in situ detailed quantification of the deposition of colloids onto an arbitrary surface and determining their concentration distribution across the bulk suspension. The system produces a relatively large field of view (approximately 330 x 245 microm) and utilizes dark-field light microscopy to visualize colloids as small as approximately 0.3 microm in diameter at the surface and in the bulk suspension with a sufficient resolution (approximately 0.5 microm). On real-time basis, the routines automate various tasks from image capturing and processing to data manipulation, extraction, and display. The extracted data include: (i) surface concentration and flux of deposited, attached, and detached colloids, (ii) surface concentration and flux of arriving and departing colloids, (iii) distribution of colloids in the bulk suspension in the direction perpendicular to the deposition surface, and (iv) spatial and temporal distributions of deposited colloids. This article provides detailed description of the system and its image processing and data extraction and manipulation routines. Representative results of the deposition of 0.3-microm-diameter polystyrene colloids onto a glass surface, from a flowing suspension in a 0.02-cm-aperture parallel-plate channel, are presented and discussed.
ABSTRACT
Dark-field light microscopy is widely employed to visualize colloidal particles much smaller than the light wavelength used. In the captured images, the colloidal particles appear, against a dark background, as bright "specks" much larger than the geometrical size of the particles. To verify whether the "specks" are for individual particles or clusters of particles, experiments are performed which used low bulk concentrations of five suspensions of monodispersed particles (approximately 0.3 microm in diameter) and a dark-field video microscopic system with an optical resolution of approximately 0.5 microm to count the particles after they all have deposited onto the inner surfaces of a parallel-plate glass channel. The average size and the size distribution of the particles are also determined at the end of each experiment. The results confirmed that the visualized "specks" are for individual particles. The measured and prepared particle bulk concentrations in the five experiments closely matched, to within +/-5%, and the measured average size of the particles and their size distribution at the end of the five experiments were in agreement with the known values.
