(197c) 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.

  References

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.