Funding NSF – CBET- 0852948

Multiscale Modeling of Flow over Functionalized Surfaces: Algorithms and Applications

Intellectual Merit: In many microfluidic, synthetic-materials, and biomedical applications there is often a need to model accurately multiscale flow phenomena across several orders of magnitude in spatio-temporal scales, hence capturing important molecular details within a near-wall subdomain but also efficiently resolving the outer flow over long simulation times. The goal of this project is to develop a validated methodology for simulating multiscale flow phenomena over functionalized surfaces with a biomedical focus. To this end, we propose a \triple-decker" flow model based on interfacing seamlessly a mesoscopic method (dissipative particle dynamics or DPD) to molecular dynamics (MD) on one side and incompressible Navier-Stokes (NS) equations on the other side. The novelty of our approach is the use of a mesoscopic layer between NS and MD - unlike previous approaches -- to facilitate a smooth transition from the atomistic to the continuum regime. Our preliminary results for simple fluids show the great potential of this method, and here we propose fundamental new developments to make the method applicable to complex fluids and to flows over functionalized surfaces. We first consider modeling of polymer brushes, i.e., an assembly of polymer chains tethered by one end to a surface, used in creating a responsive "active" surface with specialized properties. Given the large theoretical and experimental volume of works published on this topic, starting with the work of de Gennes, we will use this application as a testbed to validate the proposed methodology and evaluate its efficiency. We will then extend this multiscale framework to modeling cytoadhesion over protein-coated surfaces using the polymer brushes as model of cell surface. Our objective here is to develop a molecularly based adhesive dynamics model to complement existing mechanistic macromodels for multiparticle adhesive dynamics. Specifically, we will simulate the binding of malaria-infected red blood cells (RBCs) to functionalized walls, as was done in recent microfluidic experiments, in essence mimicking cytoadhesion in arterioles and capillaries.

Broad Impact and Outreach: The triple-decker (MD-DPD-NS) approach we propose is general and can be applied to simple and complex fluids in microfluidic or biomedical applications but also in more classical applications, e.g., control of wall shear stress using surfactants or hydrophobic surfaces. There are currently no established methods for numerical modeling of functionalized surfaces and most models involve phenomenological approaches or ad hoc interaction potentials. DPD, first popularized in Europe, is a very effective method for modeling both complex fluids and soft matter but has not yet been adapted widely in USA, and the proposed work will contribute to its further use and development. More broadly, our work on polymer brushes can be used in a wide range of industrial applications in oil recovery, automotive lubrication, colloid stabilization, and in tailoring surface properties. Similarly, our studies on cytoadhesion may provide new insight for potential new approaches to treat malaria by improved microcirculatory flow.

Education and Outreach: We will disseminate our models and the triple-decker codes as open source codes via existing external open source websites. We will organize seminar-courses open to all students at Brown University focused on multiscale modeling and applications. In addition, undergraduate students, through Brown's UTRA (Undergraduate Teaching and Research Assistantships) program, will be involved in the research projects, either during the academic year or the summer. We also plan outreach activities for inner-city high school students in a partnership with the MET school, where Brown students will be tutoring MET high school students in physics and mathematics in close collaboration with MET school teachers.

Publications

  • D. A. Fedosov and G. E. Karniadakis. Triple-Decker: Interfacing Atomistic-Mesoscopic-Continuum Flow Regimes. Journal of Computational Physics, 228(4), 1157-1171, 2009.