Disruption of polystyrene latex aggregates in capillary flow |
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Authors: | S Tang C M McFarlane Z Zhang |
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Institution: | (1) Department of Chemical Engineering and Chemical Technology Imperial College, London SW7 2BY, UK e-mail: s.tang@ic.ac.uk, GB;(2) School of Chemical Engineering University of Birmingham Birmingham B15 2TT, UK, GB |
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Abstract: | Disruption of polystyrene latex aggregates, formed in 1 M citric acid/phosphate buffer solution at pH 3.8 through diffusion-limited
colloid aggregation (DLCA) and in 0.2 M NaCl solution at pH 5.5 through reaction-limited colloid aggregation (RLCA), was studied
with respect to aggregate size and fractal nature. This was achieved using small-angle laser scattering in conjunction with
a specially designed sampling method, which brought about the elimination of the disruption of the aggregates caused by a
commercial stirrer sample unit. Aggregations were carried out in a mixture of deuterium oxide and water instead of water alone
as a solvent to minimise sedimentation resulting from the differences in density between the latex particles and the electrolytes.
An initial “steady state” in terms of aggregate size and fractal dimension was found to occur after around 20 min and 2 days
for DLCA and RLCA aggregates, respectively, at 25 °C. No aggregate disruption was detected for DLCA and RLCA aggregates after
their passing through a capillary tube for shear rates up to 1584 and 2694 s−1, respectively. At higher shear rates, significant decreases in the aggregate volume-mean diameter, D4, 3], occurred after shearing. The degree of reduction in D4, 3] was larger for DLCA aggregates in comparison to RLCA aggregates. The results would suggest that DLCA aggregates were
more subject to disruption during shearing. A high degree of disruption was observed in turbulent flow for both aggregates.
Received: 30 June 1999 Accepted in revised form: 11 November 1999 |
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Keywords: | Disruption Aggregates Size Fractal dimension Capillary flow |
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