RESEARCH
ACTIVITIES IN OUR GROUP
Our current research is on the dynamical behavior of emulsions and foams including the particlescale
and collective behavior of these systems. In addition to their rich dynamical behavior and
relevance to engineering applications, emulsions and foams are an interesting system because they
provide a wellcharacterized model system for understanding important aspects of more complicated
systems of deformable particles such as polymer blends, gels, and biological fluids.
We have worked in four problem areas which are described below:
(1)
Film drainage and drop coalescence
(2) Drop breakup
(3) Emulsion rheology
(4) Hydrodynamics of surfactantcovered interfaces
Film
drainage and drop coalescence
Recently, we developed new analytical theories and accurate numerical simulations for coalescence
of drops with clean and surfactantcovered interfaces. The focus of these studies is on the ratelimiting
step of drainage of the thin liquid film between drop interfaces just prior to coalescence.
The fundamental understanding of drop coalescence furthered by these studies is important in
engineering applications where the evolution of a drop size distribution must be reliably predicted
or controlled.
We obtained an analytical solution for the longtime asymptotic evolution of the thin liquid film
between deformable drops with mobile interfaces. This had been an unsolved puzzle since the 1978
study of Jones & Wilson [J. Fluid Mech. vol. 87, p. 263, 1978] who concluded that there was “no
prospect” for solving the nonlinear integrodifferential equation which governs the evolution of the
thin film.
In another recent study, we demonstrated that the previouslyignored influence of internal circulation
within drops qualitatively affects coalescence rates. This new hydrodynamic mechanism for
controlling drop coalescence has promising practical applications in fields such as microfluidics. A
surprising result is the prediction of flowstabilized noncoalescing drops, which may explain recent
experiments, where noncoalescence was observed but attributed to a nonhydrodynamic repulsive
force.
Drop
breakup
We developed an adaptive restructuring algorithm for computational meshes on evolving surfaces.
Resolution of the relevant local length scale on the evolving surface is everywhere maintained with
prescribed accuracy through the minimization of an appropriate mesh energy function by a sequence
of local restructuring operations. The resulting discretization depends on the instantaneous
configuration of the surface but is insensitive to the deformation history. Our algorithm made feasible
wellresolved threedimensional boundary integral simulations of drop breakup event by our
group and is being widely used for a variety of problems by research groups elsewhere.
Ultimately, our numerical simulations provide a guide for developing and testing theoretical descriptions
of drop breakup. We used our simulations to explore criteria for breakup and the dynamics
of breakup events in simple flows, and the statistics of breakup events in stochastic flows. Useful
results include the discovery that the volume of daughter drops produced by breakup events scales
with the volume of the criticalsize drop, not the the mother drop as was previously assumed in
population balance models. We developed a theory for the nearcritical dynamics of breaking drops,
according to which a single slowmode undergoes a saddlenode bifurcation at the critical point,
analogous to the Landau theory for phase transitions. Our theory provides a reliable method for
determining critical parameters from experimental data or numerical simulations.
In another study, we derived analytical expressions for the critical parameters for drop breakup in
straindominated flows. Our analysis and numerical simulations demonstrate, for the first time,
distinct coexisting stationary states for drops in Stokes flows. The coexisting states are shown to
correspond to a balance between distorting viscous stresses, and either the rotation of the drop
by the imposed flow or surfacetensiondriven relaxation of the drop shape. Coexisting coiled and
stretched configurations of polymer molecules in viscous flows may be similarly explained by the
balance of viscous stresses, and the rotation or the entropicallydriven relaxation of the molecule.
Rheology of suspensions with deformable particles
We have conducted several studies which provide a rigorous dropscale interpretation of emulsion
rheology. This work involved the development of the first manydrop threedimensional boundary integral simulations for flows of concentrated suspensions of hydrodynamicallyinteracting deformable
particles, and small deformation analyses for the dynamics of surfactantcovered drops in
dilute emulsions, and for emulsions that are concentrated up to and beyond the jamming threshold.
These studies explain the rich rheological behavior of emulsions (e.g., shear thinning viscosities,
nonzero normal stresses, and nonlinear frequency response) in terms of the interplay between the
distinct time scales of the system, including the relaxation times associated with the drop shape
and surfactant distribution, and the time scales associated with convective distortion and rotation
of the drop shape and surfactant distribution. The shape modes corresponding to the spectrum of
relaxation times reveal interesting features, such as finescale oscillatory structures at the contact
lines in jammed emulsions which contribute significantly to the stress in the system. Qualitative
features of the predicted rheology are observed in a variety of other systems, such as shearthinning
resulting from drop rotation in polymer blends and gels and transient shear stress oscillations
in micelle solutions which suggests that our work has broad application to complex fluids with
deformable particles. Indeed, our results have been used by theorists elsewhere who are attempting
to formulate coarsegrained models and generic theories of complex fluids.
Hydrodynamics
of surfactantcovered interfaces
We developed a theory for the hydrodynamics of incompressible surfactant films, which applies to a
broad class of problems where capillary stresses dominate viscous stresses. According to the theory,
constant surfactant density is maintained by Marangoni stresses (surface tension gradients) on the
interface. The situation is closely analogous to the theory of (threedimensional) incompressible
fluid flow, where constant mass density is maintained by pressure in the fluid.
We also developed a theory for film drainage between drops with surfactantcovered interfaces
which describes a hydrodynamic backflow mechanism by which compressible surfactant films hinder
coalescence more than immobile interfaces (e.g., rigid particles). An expression was derived for the
critical concentration of adsorbed surfactant below which coalescence occurs rapidly.
Liquid flow and transport in foams is another research area where our group is working. Here,
one of the principal questions is the permeability of liquid in foams and the effects of surfactants.
We developed an analytical solution for the permeability and surfactant transport in foams. Our
analysis is the first to properly incorporate Marangoni stresses and the predicted permeabilities
are twenty times larger than expected in the absence of Marangoni stresses. Recent microscopic
measurements of the bubble scale flow by research groups elsewhere support the distinct countergravity
flow pattern predicted by our theory.
PUBLICATIONS
 Loewenberg, M., Bellan, J. & Gavalas, G.R. 1987 A simplified description of char combustion.
Chem. Eng. Commun. 58, 89103.
 Loewenberg, M. & Gavalas, G.R. 1988 Steadystate reactant flux into a medium containing
spherical sinks. Chem. Eng. Sci. 43, 24312444.
 Levendis, Y.A., Nam, S., Loewenberg, M., Flagan, R.C. & Gavalas, G.R. 1989 The effects of
the catalytic activity of calcium in the combustion of carbonaceous particles. Energy Fuels 3, 2837.
 Loewenberg, M. & Gavalas, G.R. 1989 Timedependent, diffusioncontrolled reactions: the
influence of boundaries. J. Chem. Phys. 90, 177182.
 Loewenberg, M. 1989 Reactant flux into a medium containing spherical sinks: the time dependent problem. Chem. Eng. Sci. 44, 23942398.
 Loewenberg, M. & Levendis, Y.A. 1991 Combustion behavior and kinetics of synthetic and
coalderived chars: comparison of theory and experiment. Combust. Flame. 84, 4765.
 Loewenberg, M. & O’Brien, R. W. 1992 The dynamic mobility of nonspherical particles. J. Colloid Interface Sci. 150, 158168.
 Loewenberg, M.&Davis, R.H. 1993 Nearcontact thermocapillary migration of a nonconducting viscous drop normal to a planar interface. J. Colloid Interface Sci. 160, 265274.
 Loewenberg, M. 1993 The unsteady Stokes resistance of arbitrarily oriented, finitelength
cylinders. Phys. Fluids A 5, 30043006.
 Loewenberg, M. & Davis, R.H. 1993 Nearcontact, thermocapillary motion of two nonconducting drops. J. Fluid Mech. 256, 107131.
 Loewenberg, M. 1993 Stokes resistance, added mass, & Basset force for arbitrarily oriented,finitelength cylinders. Phys. Fluids A. 5, 765767.
 Loewenberg, M. 1994 Unsteady, electrophoretic motion of a nonspherical, colloidal particle
in an oscillating electric field. J. Fluid Mech., 278, 149174.
 Loewenberg, M. & Davis, R.H. 1994 Flotation efficiencies of fine, spherical particles and drops. Chem. Eng. Sci., 49, 39233941.
 Loewenberg, M. 1994 Asymmetric, unsteady Stokes flow past an oscillating, finitelength
cylinder; the macroscopic effect of particle edges. Phys. Fluids 6, 10951107.
 Loewenberg, M. 1994 Diffusioncontrolled, heterogeneous reaction in a material with a bimodal poresize distribution. J. Chem. Phys. 100, 75807589.
 Loewenberg, M. 1994 Axisymmetric, unsteady Stokes flow past an oscillating, finitelength
cylinder. J. Fluid Mech. 265, 265288.
 Loewenberg, M. & Davis, R.H. 1995 Nearcontact, electrophoretic particle motion. J. Fluid Mech., 288, 103122.
 Nichols, C.S., Loewenberg, M. & Davis, R.H. 1995 Electrophoretic particle aggregation. J. Colloid Interface Sci., 176, 342351.
 Loewenberg, M. & Hinch, E.J. 1996 Numerical simulation of a concentrated emulsion in shear flow. J. Fluid Mech. 321, 395419.
 Wang, H., Zheng, S., Loewenberg, M. & Davis, R.H. 1997 Particle aggregation due to combined gravitational and electrophoretic motion. J. Colloid Interface Sci. 187, 213220.
 Loewenberg, M. & Hinch, E.J. 1997 Collision of deformable drops in shearflow. J. Fluid Mech. 338 299315.
 Loewenberg, M. 1998 Numerical simulation of concentrated emulsion flows. J. Fluids Eng. 120, 824832.
 Manga, M., Castro, J., Cashman, K.V. & Loewenberg, M. 1998 Rheology of bubblebearing
magmas: theoretical results. J. Volcanology & Geothermal Res. 87, 1528.
 Cristini, V., Blawzdziewicz, J. & Loewenberg, M. 1998 Drop breakup in threedimensional
viscous flows. Phys. Fluids Letters 10, 17811783. [pdf]
 Cristini, V., Blawzdziewicz, J. & Loewenberg, M. 1998 Nearcontact motion of spherical
surfactantcovered droplets. J. Fluid Mech. 366, 259287. [pdf]
 Ramirez, J., Zinchenko, A., Loewenberg, M. & Davis, R.H. 1999 The flotation rates of fine
spherical particles under Brownian and convective motion. Chem. Eng. Sci 54, 149157.
 Blawzdziewicz, J., Wajnryb, E. & Loewenberg, M. 1999 Hydrodynamic interactions and
collision efficiencies of surfactantcovered spherical drops: incompressible surfactant films. J. Fluid Mech. 395, 2959. [pdf]
 Blawzdziewicz, J., Cristini, V. & Loewenberg, M. 1999 Nearcontact motion of spherical
surfactantcovered droplets: ionic surfactants. J. Colloid Interface Sci. 211, 355366. [pdf]
 Kraynik, A.M., Reinelt, D.A. & Loewenberg, M. 1999 Foam Microrheology. In Foams and Films D. Weaire and J. Banhart (eds.), Verlag MIT.
 Blawzdziewicz, J., Cristini, V. & Loewenberg, M. 1999 Stokes flow in the presence of a planar interface covered with incompressible surfactant. Phys. Fluids 11, 251258. [pdf]
 Blawzdziewicz, J., Vlahovska, P., & Loewenberg, M. 2000 Rheology of a dilute dispersion of
surfactantcovered spherical drops. Physica A 276, 5085. [pdf]
 Nemer, M., Blawzdziewicz, J. & Loewenberg, M. 2001 Linear viscoelasticity of concentrated
emulsions. In Mechanics for a new millennium, 7584, H. Aref and J.W. Phillips (eds.),
Kluwer. [pdf]
 Cristini, V., Blawzdziewicz, J. & Loewenberg, M. 2001 An adaptive mesh algorithm for
evolving surfaces: simulations of drop breakup and coalescence. J. Comp. Phys. 168 445
463. [pdf]
 Manga, M. & M. Loewenberg, 2002 Viscosity of magmas containing highly deformable bubbles. J. Volcanology & Geothermal Res. 105 1924.
 Vlahovska, P., Blawzdziewicz, J. & Loewenberg, M., 2002, Nonlinear rheology of a dilute
emulsion of surfactantcovered spherical drops in timedependent flows. J. Fluid Mech. 463,
1–24. [pdf]
 Blawzdziewicz, J, Cristini, V. & Loewenberg, M. 2002, Critical behavior of drops in linear
flows: I. phenomenological theory for drop dynamics near critical stationary states. Phys. Fluids 14 2709–2718. [pdf]
 Blawzdziewicz, J., Cristini, V. & Loewenberg, M., 2003, Multiple stationary drop shapes in
straindominated linear Stokes flows. Phys. Fluids Letters 15, L3740. [pdf]
 Patel, P.D., Shaqfeh, E.S.G., Butler, J.E., Cristini, V.,Blawzdziewicz J. & Loewenberg, M.,
2003, Drop breakup in the flow through fixed fiber beds: An experimental and computational
investigation. Phys. Fluids 15, 11461157.
 Cristini, V., Blawzdziewicz, J., Loewenberg, M. & Collins, L.R. 2003 Breakup in stochastic
Stokes flows: subKolmogorov drops in isotropic turbulence. J. Fluid Mech. 492, 231–250. [pdf]
 Cristini, V., Guido, S., Alfani, A., Blawzdziewicz, J. & Loewenberg, M. 2003 Drop breakup
and fragement size distribution in shear flow. J. Rheol. 47, 1283–1298.
 Cunha, F.R. & Loewenberg M. 2003 A study of emulsion expansion by a boundary integral
method. Mech. Res. Commun. 30, 639–649.
 Nemer, M., Chen, X., Papadopoulos, D. H., Blawzdziewicz, J.& Loewenberg, M., 2004, Hindered and accelerated coalescence of drops in Stokes flow. Phys. Rev. Letters 92, 114501. [pdf]
 Ismail A.E. & Loewenberg, M. 2004 Longtime evolution of a drop size distribution by coalescence in a linear flow. Phys. Rev. E. 69 46307.
 Vlahovska, P., Blawzdziewicz, J. & Loewenberg, M., 2005, Deformation of a surfactantcovered drop in a linear flow. Phys. Fluids, bf 17, 103103.
 Nemer, M.B., Chen, X., Papadopoulos, D.H., Blawzdziewicz, J, & Loewenberg, M., 2007,
Comment on ”Two touching spherical drops in uniaxial extensional flow: Analytical solution
to the creeping flow problem”. J. Colloid Interface Sci., 308, 1–3.
 Hashmi, S.M., Loewenberg, M. & Dufresne, E.R., 2007, Spatially extended FCS for visualizing and quantifying highspeed multiphase flows in microchannels. Optics Express, 15 65286533.
 Vlahovska, P.M., Blawzdziewicz, J. & Loewenberg, M., 2009, Small deformation theory for a surfactantcovered drop in linear flows. J. Fluid Mech., 624 293337.
 Santoro, P. & Loewenberg, M., 2009, Coalescence of drops with tangentially mobile interfaces: effects of ambient flow. Ann. N.Y. Acad. Sci. 1161, 277–291.
 Janssen, P.J.A., Anderson, P.D. & Loewenberg, M., 2010, A slenderbody theory for lowviscosity drops in shearflow between parallel walls. Phys. Fluids, 22 042002.
 Ramachandran, A., Loewenberg, M. & Leighton, D.T., 2010, A constitutive equation for
droplet distribution in unidirectional flows of dilute emulsions for low capillary numbers. Phys. Fluids, 22 083301.
