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Research Interests
Structure and micromechanics of fine particle clusters;
interfacial engineering strategies for advanced materials
processing; dispersive mixing mechanisms and modeling;
non-linear dynamics in polymer processing equipment;
entropic characterization of mixing in processing equipment;
entropic measures of mixing tailored for specific system
property assessment.
Overview of Research
Mixing is an important component of practically every
polymer processing operation. Material processability and
product properties are highly influenced by mixing quality.
Our work focuses on applying the findings of fundamental
research on mixing mechanisms in highly idealized systems to
processes taking place inside complex industrial mixing
devices, such as internal mixers or twin screw extruders.
Modeling the mixing process in real mixing equipment
requires not only an understanding of the mechanics of flow,
but also selection of appropriate indexes to quantify the
mixing process. Our research efforts include developing and
testing mixing indexes and criteria for assessing both
dispersive and distributive mixing efficiency in various
batch and continuous polymer processing equipment. Through
the development of a general framework by which a variety of
processes and machines can be analyzed, our research impacts
on both the polymer processing industry as well as on
equipment manufacturing and evolution of new generations of
compounding machines.
Another broad area of interest focuses on modeling and
evaluation of complex dispersion kinetics for fine particle
clusters. Fine particle clusters are widely used in chemical
and material processing. Very often, the quality of the
resulting product is largely dependent on the degree of
dispersion of the clusters into the background matrix. Our
research is aimed at identifying and understanding the
physical and chemical characteristics of the solids and
processing media that govern dispersion mechanisms and
kinetics. We are studying the links between fine structural
details of particle clusters, interfacial characteristics
and flow geometry in agglomerate dispersion. Towards this
goal we have developed a number of experimental and
analytical techniques that provide appropriate information.
For instance, we have developed the concept of
dispersibility maps to generalize the interfacial
interactions between fillers and matrix fluids. We have also
developed some experimental devices that can be used to
monitor the course of dispersion in various flow geometries.
Our research impacts on both existent technologies but also
on the development of new strategies for the fabrication of
advanced materials.
Another thrust of our research is the development of
interfacial engineering strategies for advanced materials
processing. One example is the use of particles as
compatibilizers in blends of immiscible polymers. Another
example is the use of responsive binders designed to
actively control the cohesivity of fine particle clusters.
These include binder additives, which can provide a variable
augmentation to the agglomerate cohesivity, or thermally
responsive gels (or other intercalants) that can be used to
reduce the agglomerate cohesivity to below its native
strength. We are exploring the development of binders to be
used as dispersant aids in particle assemblies spanning a
range of particle length scales from nanometer to millimeter
in size.
Current Activity
One of the main thrusts of our current research focuses on
identifying the parameters governing dispersion of fine
particle clusters in various media and analytical modeling
of the process. We have demonstrated that dispersion
behavior of porous agglomerates in linear flow fields is
affected by the degree of matrix infiltration in the
agglomerate as well as by cluster permeability. The presence
of fluid within the agglomerate modifies its cohesive
strength and affects the mechanics of stress transmission
from fluid to agglomerate. We are currently investigating
the wetting and spreading behavior of binder liquids on
individual pairs of interacting particles with the aim of
better engineering powder processing operations. In order to
quantitatively assess the influence of viscous binder on
agglomerate cohesivity we have developed an accurate
analytical expression for the total inter-particle force of
interaction induced by the fluid. A non-dimensionalization
algorithm makes this analytical expression independent of
particle size-scales and varied dynamics of the
interactions. We thus have the capability of modeling
pairwise interactions amongst particles with and without
binder. Integrating these in a suitable computer simulation
can be used to predict transmission of forces and hence,
failure thresholds in real-world agglomerates, by
appropriate interspersing of the wet and dry contacts.
We have recently demonstrated the occurrence of two
distinct mechanisms of hydrodynamic dispersion for
fine-particle agglomerates infiltrated to different extents
by the suspending fluid, namely cohesive and adhesive
failure. Dispersion by cohesive failure occurs when
hydrodynamic forces are sufficient to induce the removal of
unilfiltrated fragments from the parent agglomerate or the
breakage of wetted fragments from an infiltrated portion of
the parent agglomerate. Adhesive failure is characterized by
a breakage at the interface between the infiltrated
periphery of an agglomerate and its dry core.
In most previous analyses of the dispersion of particle
agglomerates, both experimental and modeling studies have
focused on steady shear flows of controlled magnitude.
Currently we are expanding our studies to time dependent
flow fields, which are more relevant to industrial
practices. Our emphasis is on dynamic phenomena associated
with the mechanical behavior of agglomerates and how
temporally varying shear or elongational flow fields can
stimulate these phenomena. We intend to predict dispersion
in realistic, time-varying flow fields and to elucidate the
links between cluster structure, interparticle and
particle-fluid interactions, and the details of the
processing history. Our simulations of agglomerate
dispersion use the discrete/distinct element method (DEM).
Implicit in the model is the potential for predicting the
impact of agglomerate size, structure and morphology effects
on dispersion dynamics.
Another broad area of interest focuses on developing and
testing mixing indexes and criteria for assessing dispersive
and distributive mixing efficiency in polymer processing
equipment. We have recently demonstrated that Renyi
entropies offer a rigorous, practical and efficient means by
which to characterize distributive mixing via fractal
dimensions. The independence of the Renyi entropies from the
system geometric profile provides an index to be uniformly
applied to different types of processing equipment. We have
recently expanded the use of Shannon entropy for
simultaneous characterization of dispersive and distributive
mixing and for assessing color homogeneity.
Recent Publications
“Index for simultaneous dispersive and distributive mixing
characterization in processing equipment,” K. Alemaskin,
I. Manas-Zloczower and M. Kaufman, International Polymer
Processing, 19(4), 327-334 (2004).
“Influence of the Extruder Geometry on Laminar Mixing:
Entropic Analysis,” M. Camesasca, I. Manas-Zloczower
and M. Kaufman, Plastics, Rubber & Composites:
Macromolecular Engineering, 33(9/10), 372-376 (2004).
Recent Presentations
Awards
Named Society of Plastics' Engineers (SPE)
Fellow 2006 Elected co-chairman of the Gordon Research Conference on
Computer Aided Engineering for 2005, Chairman in 2007
Technical co-chairman of the Polymer Processing Society
Annual Meeting, June 2004
External international expert for the Foundation of Science
and Technology in Portugal, 2003
Book Advisory Board, Hanser Publishers, 2001
Editor-in-Chief, Journal of Polymer Engineering, 1999
International Representative for the Americas in the Polymer
Processing Society Executive Committee
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