brochure - UBALDO M. CÓRDOVA

Ubaldo M. Córdova-Figueroa Research Group
low Reynolds fluid mechanics, transport
processes, and colloidal sciences
Life best survives at nicely intermediate conditions—not too hot, not too
cold; not too big, not too small—just right. Many interesting phenomena
occur in the middle. Our research group thus focus somewhere between the
very small and very large—on the colloidal regime. Here we find micro- and
nanoparticles large enough in comparison to the surrounding fluid molecules
that they ‘see’ the fluid as a continuum, yet are still small enough to sustain
appreciable Brownian motion due to collisions with the aforementioned
molecules. At their ‘simplest’ level, colloidal particles play an important role
in applications such as ceramics, foods, paints, and photonic materials. keywords: particulate and multiphase processes, nonequilibrium statistical
mechanics, colloidal dispersions, transport phenomena, self-propulsion,
Ubaldo M Córdova-Figueroa
Assistant Professor
University of Puerto Rico-Mayagüez
Department of Chemical Engineering
Phone: (787) 832-4040 x. 5844
Email: [email protected]
Twitter: @cordovaresearch
2008 Ph.D. Chemical Engineering, California Institute of
Technology, Thesis Advisor: John. F. Brady
2006 M.S. Chemical Engineering, California Institute of
2003 B.S. Chemical Engineering, University of Puerto
Rico, Mayagüez
2011 NSF CAREER Award Recipient
Dynamic Simulations of Reconfigurable Complex Fluids from
Janus and Catalytically-Driven Colloidal Particles
This research combines Prof. Córdova-Figueroa’s expertise in
low Reynolds number hydrodynamics and colloidal suspensions
to study the emerging field of complex fluids based on ‘twofaced’ Janus particles—particles which have two distinct sides—
that depending on their surface functionality could lead to
novel material properties and aggregation/self-ordering
abilities or to autonomous behaviors using on-board chemical
motors operating far from equilibrium. This NSF CAREER
proposal presents research and educational activities designed
to elucidate important aspects of reconfigurable complex fluids
—active materials that could change and relax their structure
with minimum or no external intervention using as precursors
Janus and catalytically-driven colloidal particles. The research
efforts are divided in two main tasks. The first one focuses in
studying the motion, rheology, and structural organization of
Janus particle suspensions guided by a combination of fluid
flows and external forces. Different behaviors are expected
depending on the interparticle force between the ‘Janus’ faces
of the particles (e.g., hard sphere, attractive, soft). The second
research task aims at understanding collective motion of
catalytically-driven Janus particle suspensions. A simple
‘colloidal’ approach to autonomous motion via chemical
reactions will be used and implemented based on classic
multicomponent diffusion and depletion flocculation theory.
Simple elementary dynamic units operating with specific rules
and exploiting chemotaxis will be proposed as ‘elements’ for
future reconfigurable materials. These efforts will be
accomplished by Brownian/Stokesian dynamics simulations
and experiments with collaborating partners.
Ubaldo M. Córdova-Figueroa
Research Group
Our group's research interests are in fluid
mechanics, transport processes, and colloidal
sciences, with a special interest in problems at the
interface between continuum mechanics and
statistical mechanics. One area of research concerns
fundamental studies of complex fluids based on
Janus and catalytically-driven colloidal particles.
Complex fluids is a generic label for materials that
are composed of microstructural elements that
interact via colloidal, hydrodynamic, and Brownian
forces. Familiar examples of such fluids are
suspensions, colloidal dispersions, liquid crystals,
ferrofluids, electrorheological fluids, and polymer
solutions and melts. In these systems the basic
“Studies of Janus and self-propelled
particles in general could bring into
reality a wide range of novel
applications in materials science, nanoand biotechnology, lab-on-a-chip
systems, and drug/cargo delivery.”
question is one of understanding and predicting the
relationship between the material's microstructure
and its macroscopic properties.
Twitter: @CordovaResearch
If you are interested in joining our group, send an
email to: [email protected]
Group Members
From left to right:
Glenn C. Vidal
(Ph.D. student)
Efrain Aymat
(M.S. student)
Misael Diaz
(Ph.D. student)
Christian Santoni
(M.S. student)
Dr. Sergey Shklyaev
(postdoctoral fellow)
Guided motion of
magnetic osmotic
'non-motile' metabolically active
bacterium in the presence of an uniform
reactant concentration. It has been
observed that a biological cell permeable
to fluid molecules but not to solutes—a
semipermeable membrane—moves away
from concentrated regions. This
phenomenon results from an imbalance
in the osmotic pressure between the two
fluids separated by a cell membrane,
leading to a fluid flow from inside the cell
to high concentration regions in the outer
fluid and from low concentration regions
in the outer fluid to inside the cell. Such
motion is known as osmophoresis. In the
case of metabolically active non-motile
bacteria it is unclear how osmophoresis
will be affected by a chemical reaction at
the surface of the cell that can alter the
concentration field and, therefore, the
osmotic pressure gradient ‘sensed' by the
bacterium. In this study, we consider an
asymmetric surface chemical reaction at
the bacterium surface (e.g., degrading
transmembrane enzymes) causing a local
osmotic pressure gradient autonomously
and thus fluid flow across the membrane.
We demonstrate that this fluid flow
propels the bacterium toward less
concentrated regions and that its velocity
depends on the reaction speed, its size,
and membrane and solvent properties.
Reaction-driven propulsion of colloidal
particles, such as osmotic motors, consists
of the localized generation of a
concentration gradient by an on-board
surface chemical reaction. As shown in
recent experiments, the directed motion
of these particles is hindered by their
rotary Brownian motion and thus
preventing its potential to be completely
realized. However, if the self-propelled
particle is magnetized (or contains a
magnetic dipole), its directionality can be
controlled externally by a magnetic field
and the conversion from chemical energy
into motion becomes more effective. In
this work, we investigate the short and
long-time behavior of osmotic motors
immersed in a dispersion of reactant
particles subject to a magnetic field using
Brownian dynamics simulations. The
strength of the magnetic field is
controlled by the Langevin parameter,
which ultimately dictates the long-time
Bacterial diffusion: A
behavior of the osmotic motor. The
rotational and translational velocity of
the osmotic motor for different surface
reaction speeds, reactant particle
Enterococcus faecalis—a gram-positive nonconcentrations, and Langevin parameters
motile bacterium that inhabits in the
are investigated. intestinal tract of humans—metabolizes
carbohydrates to lactic acid. The
diffusive behavior of Enterococcus
faecalis has been studied by varying the
propulsion of semiconcentration of metabolizable
permeable particles
substrates. For comparison purposes
Recent studies have shown that the 'non- Enterococcus casseliflavus—a similar but
motile' bacteria Syntrophus aciditrophicus has flagellated bacterium—was studied under
the ability to sense its chemical
the same conditions. Diffusivity
environment—an essential step for
measurements were obtained using video
chemotaxis typically observed in 'motile'
microscopy. Results show that the
microorganisms (e.g., Escherichia coli). In diffusivity of the motile microorganism
light of these findings, new questions
decreases with increasing substrate
arise. Could self-propulsion take place
concentration until it reaches a plateau.
naturally in non-motile metabolically
On the other hand, the diffusivity of the
active bacteria without the aid of
non-motile microorganism shows
external gradients or forces? What
surprising trends in the presence of
conditions are necessary for this to occur? substrates. To rule out the possibility that
These questions motivate us to propose a changes in the diffusivity of the nonsimple model for self-propulsion of a
motile bacterium are not owed to
viscosity variations of the fluid, we have
found that the viscosity changes by less
than 5% in the range of studied
concentrations. A comparative study with
micron-sized polystyrene particles at the
same conditions demonstrates the
effectiveness of our method. The
hypothesis suggested by our results is that
substrate intake and inhibition
mechanisms are responsible for the
behavior observed in diffusivity
We study the long-time self-diffusivity of
a probe particle in a dilute suspension of
bath particles. A first order chemical
reaction of the bath particles (reactant)
takes place at the surface of the probe
(catalytic) particles; both types of
particles are assumed solid spheres of the
radii large in comparison with the solvent
molecules. We neglect hydrodynamic
interactions between the particles and
calculate the first correction—
proportional to the volume fraction of
the bath particles—to the long-time selfdiffusivity. In motionless disperse
medium, this very correction is negative
and depends on the Damköhler number,
which is a measure of relative impacts
between chemical reaction and diffusion.
With increase in the Damköhler number,
the absolute value of the correction
initially grows and then decay inversely
proportional to the Damköhler number.
In case of advection of the catalytic
particle through the reactant ones, the
effect of chemical reaction is more
complicated. The intensity of advection
is characterized by the Péclet number.
The longitudinal and transversal
components of the self-diffusivity differ,
since there is a preferential direction due
to the advection. However, the qualitative
behavior of these two components with
variation of the problem parameters is
similar, only the quantitative distinction is
found. In the absence of chemical
reaction, the corrections to the selfdiffusivity change their signs with
increase in the Péclet number and
become positive. The chemical reaction,
in turn, rather weakens this effect; again
with growth of the Damköhler number,
the correction to the self-diffusivity
Graduate Programs in Chemical
Engineering at UPRM
The UPRM Department of Chemical Engineering offers
programs leading to M.S., M.E., and Ph.D. degrees. Graduate
studies at UPRM offer you the opportunity to do leading-edge
research in any of a broad range of innovative areas; to work
with our dynamic faculty, each a leader in his or her chosen
specialty; and to take advantage of the extensive resources
within the department, throughout the UPRM, and in the
intellectually and culturally rich Mayagüez area.
Today, ten years after the establishment of the PhD program
and almost at the 40th anniversary of the masters program, the
milestones achieved include: 19 faculty members active in
research (3 CAREER Award recipients; 1 PECASE awardee),
29 PhDs and 191 masters granted, 51 students currently
enrolled, over 100 peer-reviewed publications during the last
five years (32 in 2010), and over $3 million dollars in research
equipment acquired from external funding. In addition, our
faculty research efforts contribute over $4 million in external
funds (e.g., NSF, NIH, NASA, etc.) each year.
Students are supported through Teaching Assistantships,
Research Assistantships, or other special scholarships.
Complex Fluids
Transport Phenomena
Apartments and houses can be rented in Mayagüez and nearby
towns at prices ranging from US $200-400 per month.
For additional information visit us at:
Department of
Chemical Engineering
Materials Science
Renewable Energy
Center for
Center for Pharmaceutical
Research Areas
Student Life in Puerto Rico
Competitive Research in an Exotic Destination
Research: The University of Puerto Rico offers a centennial
history full of opportunities and unique cultural experiences not
found in the rest of the world. This place impacts the scope and
reach of our research. Graduate studies could be tough, but as a
student, take some time to explore the tropical island of Puerto
Rico, where you can find local exotic hideaways, miles of white
sandy beaches, mountains and valleys, and many other natural
wonders. In addition to the natural splendors you will find
yourself surrounded by warm and friendly people. This is the
perfect place to relax after constant hard work.
the island became Puerto Rico and its capital San Juan. The
United States anglicized the name to "Porto Rico" when it
occupied the island in 1898 after the Spanish-American War.
This spelling was discontinued in 1932.
Brief history: Christopher Columbus landed in Puerto Rico
in 1493, during his second voyage, naming it San Juan Bautista.
The Taínos, the indigenous people, called the island Boriquén
Tierra del alto señor ("Land of the Noble Lord"). In 1508, the
Spanish granted settlement rights to Juan Ponce de León, who
established a settlement at Caparra and became the first
governor. In 1519 Caparra had to be relocated to a nearby
coastal islet with a healthier environment; it was renamed
Puerto Rico ("Rich Port") for its harbor, among the world's best
natural bays. The two names were switched over the centuries:
Culture: Puerto Ricans are known for their warm hospitality,
often considered very friendly and expressive to strangers.
Greetings are often cordial and genuine. Puerto Ricans are best
known by speaking using lively hand and facial gestures, as
hand and body language are important forms of
Food: Although Puerto Rican cooking is somewhat similar to
both Spanish, Cuban and Mexican cuisine, it is a unique tasty
blend of Spanish, African, Taíno, and American influences,
using such indigenous seasonings and ingredients as coriander,
papaya, cacao, nispero, apio, plantains, and yampee.