*research*

*research**
theme*

*cf** ^{2}*

**We are studying how flexible (polystyrene, long DNA) and semiflexible
(PBZT, actin) macromolecules interact with the flow at the molecular level by
applying high-resolution fluorescence microscopy, shear and extensional rheometry, and non-equilibrium Brownian Dynamics. **

**We are applying similar molecular models to understanding the collapse
of semiflexible objects in bad solvent into toroidal
shapes—e.g., DNA in solution with multivalent ions (with Prof. MacKintosh, Vrije Universiteit ****Amsterdam****). **

**We are also studying the translocation of polymers and biopolymers in nanopores by Brownian Dynamics, Molecular Dynamics, and statistical
mechanics (with Profs. Kolomeisky and Clementi, ****Rice**** ****University****).****
**

**Rheometry****, neutron and light
scattering, AFM, TEM, and molecular modeling, are applied to analyzing how the
degree of intramolecular crosslinking
affects the solution and flow behavior of polymer nanoparticles,
controlling the transition from particles to coils—particoils
(with Prof. Wong, ****Rice**** ****University****). **

**Detailed single-cell mechanics models are being developed based on
nonlinear viscoelasticity and massively parallel
finite element computations to understand how flow affects the stress on the
cell membrane during growth, in an effort to controlling the in-vitro growth of
biomaterials (with Prof. Zygourakis, Rice
University). **

**Cell deformation models are coarsened for application to hemolysis in medical devices such as blood pumps (with
Prof. Behr, ****Rice**** ****University****). **

**The solution behavior of Single-Walled NanoTubes
in superacids is being studied by rheometry,
optical microscopy, and scattering, to design optimal liquid crystalline
solutions for successfully spinning macroscopic, continuous, neat fibers of SWNTs (with Prof. Smalley, Rice University). **

**We are simplifying the single-molecule models of nearly rigid polymers
by Galerkin-projecting them onto convenient basis
functions to yield highly efficient, yet accurate, stochastic models (with
Prof. Wiggins, ****Columbia**** ****University****). **

**The molecular models that are being developed and applied to understand
single-molecule behavior of macromolecular solutions (from flexible to nearly
rigid) are being coarsened through projection techniques based on an extension
of local equilibrium thermodynamics in order to develop equations for
expectation values of microstructural features of
flowing macromolecular liquids; the coarse-grained models are used in
massively-parallel finite elements codes for modeling, analyzing, and
optimizing processes on larger length scales—from microfluidics
(~****m****m), to coating (with Prof. Carvalho, Pontificia Universidade Catolica do Rio de Janeiro) and ink-jet printing (with
Prof. Basaran, Purdue University) (~ 10 to 500 ****m****m), to polymer
processing (~ 100 ****m****m to beyond few mm). **

**We also investigate the rheological behavior of emulsions, and relate it
their physical-chemical properties, which we can control in the formulation
(with A. Peña, ****Rice**** ****University****).**

*specific**
areas of research*

*Microstructured** liquids*

*Free surface flows*

*Computational modeling of process
flows*

*Visualization of flowing single DNA
molecules*

*Rheology and phase behavior of
Single-Walled Carbon Nanotubes*

*Rheology and microstructure of
Polymeric Nanoparticles (particoils)*

*Rheology and microstructure of
Emulsions*

*Single-molecule behavior of
semiflexible macromolecules*