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Brownian coagulation at high concentration
1Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zürich, Switzerland.
Langmuir : the ACS Journal of Surfaces and Colloids
|August 10, 2007
Summary
Particle growth accelerates significantly at higher concentrations, deviating from classic theories. Simulations show self-preserving size distributions form even in concentrated suspensions, though they broaden with increasing particle volume fraction.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Chemical Engineering
Background:
- Brownian coagulation is a key process in particle growth.
- Existing models, like Smoluchowski's, are well-established for dilute systems.
- High particle concentrations introduce complexities not fully captured by dilute models.
Purpose of the Study:
- Investigate particle growth via Brownian coagulation in concentrated suspensions.
- Evaluate the accuracy of classic coagulation models at high particle volume fractions.
- Determine the influence of concentration on self-preserving size distributions (SPSDs).
Main Methods:
- Solving Langevin dynamics (LD) equations for individual particle trajectories.
- Simulating polydisperse suspensions across a range of particle volume fractions (phis).
- Monitoring the attainment and characteristics of SPSDs.
Main Results:
- Classic Smoluchowski theory is accurate only below 0.1% particle volume fraction.
- Coagulation rates are 4-10 times faster at 10-20% phis compared to classic predictions.
- SPSDs develop in concentrated suspensions (up to 35% phis) but broaden with increasing concentration.
- A new overall coagulation rate is proposed for high concentrations.
Conclusions:
- Particle coagulation kinetics are strongly concentration-dependent.
- Existing models underestimate coagulation rates at high particle concentrations.
- Concentration affects SPSD characteristics, broadening them as volume fraction increases.
- Fractal agglomerates may only temporarily exhibit SPSDs due to increasing effective volume fraction.
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