Matteo Pasquali

Research Interests:

Micro- and nanostructured liquids

Interfacial and biological flows

Multiscale modeling of complex flows of complex fluids

Carbon nanotubes in liquids

Education:

Laurea (1992) University of Bologna, Italy

Ph.D. (1999) University of Minnesota

My research focuses on processing flows of microstructured liquids. Micro-structured liquids are ubiquitous in the chemical, polymer processing, coating, food, and biomedical industries. Theoretical and computational modeling of flow and transport in microstructured liquids will be a very important tool to design new processes and apparatus that can produce defect-free products at high rate with minimal environmental impact.

Conventional transport laws based on classical irreversible thermodynamics fail to describe transport in liquids like polymer melts, solutions, blood, and dough. In recent years, two new approaches have appeared to model flow and transport in microstructured liquids. One method (mesoscopic) introduces field variables obeying transport equations to represent average local values of the liquid microstructure. The other method (micro-scopic) represents the microstructure by means of a large number of micromechanical contrivances distributed in the flow volume and following stochastic differential equations. The equations of the mesoscopic models include several phenomeno-logical coefficients, whereas the microscopic models depend on few parameters that can be estimated often from knowledge of the liquid's molecular structure. Microscopic models are presently impractical for process modeling because their equations are computationally much more expensive than those of the mesoscopic models.

Another important open problem in the study of polymeric liquid flow is the experimental determination of the interaction of flow and microstructure. Conventional techniques (e.g. flow birefringence) are now being ported from rheometric flows to prototype process flows. Meanwhile, new methods like fluorescence microscopy have proven effective to study the dynamics of polymeric liquids in rheometric flows.

Modeling process flows with mesoscopic rheological theories: The current approach to computational modeling of complex flows of a polymeric liquid relies on choosing a constitutive equation for the stress based on a shear flow characterization of the liquid. The constitutive equation is then solved together with the mass and momentum transport equations. If flow predictions and measurements do not agree, another constitutive equation is selected and solved. This procedure is very labor-intensive and rarely succeeds. I am developing a set of algorithms that will automatically search the parameter space of a family of mesoscopic constitutive equations, compute flow states, compare computations and experiments, and select the constitutive equation that correctly predicts the flow of the liquid in a particular process.

Solution of microscopic transport equations in process flows:Microscopic models have not been used yet to compute free surface flows of polymer melts and solutions. A few interesting studies have recently shown that it is possible to compute simple two-dimensional flows using microscopic models (Ottinger 1996). I am interested in solving free surface flows of polymeric liquids described by microscopic models. The results of the detailed microscopic simulations can be used to improve the mesoscopic models.

Visualization of single DNA molecules in process flows:DNA molecules behave qualitatively as ordinary polymers. DNA can be marked with fluorescent stains and visualized by optical microscopy (Perkins et al. 1994) and is an attractive model system to study how macromolecules flow and deform. I have used DNA molecules to study the flow and deformation field in a roll-and-knife coating flow, and I am going to study other process flows. I am also working on improving our current image acquisition and analysis techniques to enhance image quality and determine automatically the conformation and velocity of the flowing DNA. The results of these studies clarify the interaction of polymer conformation and flow structure, and can be used to improve the theoretical models of transport in polymeric liquids.

Selected Publications

1. L. M. Ericson, H. Fan, H. Peng, V. A. Davis, W. Zhou, J. Sulpizio, Y. Wang, R. Booker, J. Vavro, C. Guthy, A. N. G. Parra-Vasquez, M. J. Kim, S. Ramesh, R. K. Saini, C. Kittrell, G. Lavin, H. Schmidt, W. W. Adams, W. E. Billups, M. Pasquali, W.-F. Hwang, R. H. Hauge, J. E. Fischer, and R. E. Smalley, Macroscopic Neat Single-Walled Carbon Nanotube Fibers. Science, 2004, accepted.
2. M. Pasquali, Swell properties and swift processing. Nature Mater., 3, p. 509-510, (2004), (Invited News & Views Article).
3. M. Bajaj, P. P. Bhat, J. R. Prakash, and M. Pasquali, Micro-Macro simulation of viscoelastic free surface flows using the Brownian configuration fields method. Proc. XIVth Int. Congr. on Rheology, Seoul, Korea, (22-27 August 2004), accepted (June 2004).
4. V. A. Davis and M. Pasquali, Macroscopic Fibers of Single-Walled Carbon Nanotubes. In Nanoengineering of Structural, Functional and Smart Materials, Eds. M. Schulz, A. Kelkar, and M. Sundaresan, CRC Press, accepted (May 2004) [invited review article].
5. D. Arora, M. Behr, and M. Pasquali, Blood Damage Measures for Ventricular Assist Device Modeling. Artificial Organs, accepted (April 2004).
6. X. Xie and M. Pasquali, A New, Convenient Way of Imposing Open-flow Boundary Conditions in Two- and Three-dimensional Viscoelastic Flows. J. Non-Newtonian Fluid Mech., accepted (February 2004).
7. M. Pasquali and L. E. Scriven, Theoretical modeling of microstructured liquids: a simple thermodynamic approach. J. Non-Newtonian Fluid Mech., 120, p. 101-135, (2004).
8. R. Duggal and M. Pasquali, Visualization of Individual DNA Molecules in a Small-scale Coating Flow. J. Rheol., 48, p. 745-764 (2004).
9. S. Ramesh, L. M. Ericson, V. A. Davis, R. K. Saini, C. Kittrell, M. Pasquali, W. E. Billups, W. W. Adams, R. H. Hauge, R. E. Smalley, Dissolution by Direct Protonation and Nematization of Pristine Single Walled Carbon Nanotubes in Superacids. J. Phys. Chem. B, 108, p. 8794-8798 (2004).
10. A. Montesi, M. Pasquali, and F. C. MacKintosh, Collapse of a semiflexible polymer in poor solvent. Phys. Rev. E, 69, 021916 (2004).

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