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  • Progress in Improvement Study on the Turbidity Measurement of the Absolute Coagulation Rate Constant
    Author:   | Date:2006-06-01   | Click Rate:    | 【Close
    The knowledge of the stability and coagulation kinetics of colloidal systems is crucial for various applications in chemical, food, pharmaceutical, and material industries, environmental engineering, as well as in biotechnology and nanotechnology. The absolute coagulation rate constant is an important parameter to characterize the coagulation kinetics of colloidal systems and its accurate experimental data is particularly important for the development of relevant theories or for deriving information of colloidal interactions. To determine the absolute coagulation rate constant of suspensions, the turbidity measurement has been extensively adopted because of its simplicity and easy implementation. However, to determine the absolute coagulation rate by the turbidity measurement, the difference between extinction (or attenuation) cross sections of one doublet or dimer (two adhered particles) and of two single particles have to be evaluated from theory. For spheres the extinction cross section can be calculated exactly from the Mie theory. However, for hard sphere particles, like polystyrene latex, as considered in our study, the doublets are not spherical so that it can not be calculated exactly by Mie theory. And the existing theories used to calculate the extinction cross sections of doublets for treating the turbidity measurement are only valid for small particles. Thus, until now the application of this methodology is still limited only to suspensions of small particles. To improve the applicability of the turbidity measurement, T-matrix method has been proposed by researchers of NML of our institute to accurately calculate extinction cross sections of real doublet in the turbidity measurement. In addition, they adopted a special experimental approach, by using different particle-sized (radius = a) suspensions at incident wavelengths (λ) ranging from near infrared to ultraviolet light, to expose the physical nature reflected in the turbidity measurement and to examine the performances of different theoretical approaches. Their experiments show that the rate constants derived from all previous theories become untenable as the size parameter (α=2πa/λ) increases. In contrast to these existing theories, the T-matrix method provides a robust solution which is effective in extending the applicability range of the turbidity methodology and increasing measurement accuracy. The relevant paper has been published in Langmuir (2006, Vol 22, Issue 11, on pages 4946-4951).
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