457437 Development of Population Balance Model and Semi-Mechanistic Layering Kernel for Two Stage Heteroaggregation of Oppositely Charged Micro- and Nano-Particles
Development of Population Balance Model and Semi-mechanistic Layering Kernel for Two Stage Heteroaggregation of Oppositely Charged Micro- and Nano-particles
Anik Chaturbedi, Nina Shapley, Rohit Ramachandran
Rutgers, the State University of New Jersey, Piscataway, NJ, USA 08854
In colloid science, heteroaggregates (aggregates of particles that are different in various aspects such as size, surface charge) are gaining popularity due to their versatile applicability. The properties of these heteroaggregates are affected by the properties of the constituent particles as well as the size of the heteroaggregates, which in turn is influenced by the initial relative concentration of the constituent particles in the system. Different initial relative concentrations lead to different regimes in the system and either facilitates or prevents heteroaggregate formation. Traditionally, core-shell particles, produced by heteroaggregation have been used for xerography, printing ink, drug delivery applications. Customized heteroaggregates for instance can also be used for water purification applications (Yu, et al., 2013), based on the idea that oppositely charged components of the heteroaggregates will adsorb toxic anions and cations such as Cadmium, Mercury, Lead, Chromium, Molybdenum, Vanadium, Arsenic from waste-water.
In this work, the heteroaggregation of alginate microparticles and chitosan nanoparticles has been studied. Since these particles are hydrogels, very different in terms of size (alginate particles are about 130 times bigger in diameter than the chitosan particles), and are oppositely charged, this system is inherently different from the commonly studied systems consisting of charged nanoparticles and negligibly charged microparticles (Zhang, et al., 2008). We assume that the heteroaggregation process, in this case, happens in two stages. Firstly, the positively charged, small chitosan particles are attracted to the negatively charged, big alginate particles dominantly due to the electrostatic force and form a layer around the latter. The particles formed are referred to as monoaggregates. In the second stage, depending on the composition and net surface charge of the monoaggregates, they either repel each other or alternatively attract each other; agglomerate and form big heteroaggregates. There are various forces in play in this system such as van der Waals, electrostatic, hydration. The complex dynamics resulting from the interaction of these forces is modeled using a population balance model with a semi-mechanistic layering kernel developed specifically for the first stage of heteroaggregation to get an accurate particle size distribution at the end of the layering process of chitosan nanoparticles on alginate microparticles, for use as the initial particle size distribution for the second stage of heteroaggregation. Using this model, the relation between the initial relative concentration of alginate and chitosan with the final particle size distribution is studied. Also, the particle size distributions at the end of the process obtained from the model are compared with experimentally obtained particle size distributions from laser diffraction spectroscopy and microscopic images of the particles to validate the model. Results show good agreement between model and experiment. The presence of different heteroaggregation regime is observed in both the experiment results and model calculations.
Yu, K., Ho, J., McCandlish, E., Buckley, B., Patel, R., Li, Z., & Shapley, N. C. (2013). Copper ion adsorption by chitosan nanoparticles and alginate microparticles for water purification applications`. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 31-41.
Zhang, F., Long, G. G., Jemian, P. R., Ilavsky, J., Milam, V. T., & Lewis, J. A. (2008). Quantitative Measurement of Nanoparticle Halo Formation around Colloidal Microspheres in Binary Mixtures. Langmuir, 6504-6508.
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