LSTM GROUP:  Dr. Pavlos Stephanou

Research Associate

Research summary

A major theme of our research work is the development of reliable constitutive models for describing the dynamics and flow behavior of complex polymeric fluids. To this, we rely on the use of non-equilibrium thermodynamics (NET), in particular on the Generalized Bracket and GENERIC formalisms, for developing closed-form balance equations for the fundamental hydrodynamic fields. No matter what the system is (say biological or chemical), it must obey the laws of thermodynamics. In particular, when the system is beyond equilibrium (e.g., under the influence of a flow field), its time evolution must be dictated by the laws of non-equilibrium thermodynamics (NET). This is exactly the reason why in our work we employ NET: by construction the new constitutive models obey the laws of thermodynamics. So far, we have developed generalized constitutive models for polymer melts, polymer solutions, and polymer nanocomposites. Currently, we are using NET to develop constitutive models for biomolecular fluids such as blood.

In most cases, the resulting constitutive equations contain parameters whose values are not known. To overcome this, we resort to atomistic simulations, both (equilibrium) Molecular Dynamics (MD) and non-equilibrium MD (NEMD), and coarse-grained Brownian Dynamics (BD) simulations. This allows us to develop interconnections between three different levels of system description: the atomistic or microscopic, the mesoscopic, and the macroscopic. As one moves from the atomistic to the macroscopic level (coarse-graining), the degrees of freedom of the system are significantly reduced, which results in dramatic reductions in computational demands. However, coarse-graining must be done carefully to avoid the loss of important information. Our work connects the three levels through the development of scale-bridging methodologies, and the outcome is a set of, closed-form, constitutive equations for the time evolution of the structural and hydrodynamic fields selected to describe the system. Overall, the building blocks of our bridging methodology are the following: 1) At the atomistic level: we use atomistic MD and NEMD simulations to simulate the real system to obtain the values of important parameters entering the description of the system at the mesoscopic level. 2) At the mesoscopic level: we design coarse-grained simulations (e.g. BD simulations) which provide information about the evolution of the system for much larger time spans than what is addressed by atomistic simulations. 3)At the macroscopic level: we use NET to derive generalized constitutive models for complex systems whose parameters are evaluated from the previous levels.

Education

  • 2011: Ph.D., Department of Chemical Engineering, University of Patras
  • 2006: Diploma in Chemical Engineering, University of Patras

Research experience

  • 09/2016 – present: Post-doctoral research fellow, Department of Mathematics and Statistics, University of Cyprus, Cyprus (with Prof. Georgios Georgiou).
  • 03/2015-09/2016: Post-doctoral research fellow, Department of Materials, ETH-Zürich, Institut für Polymere, Zürich, Switzerland (with Profs. Hans Christian Öttinger and Martin Kröger).
  • 09/2011-02/2015: Post-doctoral research fellow, Department of Mathematics and Statistics, University of Cyprus, Cyprus (with Prof. Georgios Georgiou).
  • 09/2008-04/2009: Ph.D. Research Assistant, Department of Chemical and Biomolecular Engineering, The University of Tennessee-Knoxville, TN, USA (with Profs. Brian J. Edwards and Bamin Khomami).
  • 09/2006-07/2011: PhD studies, thesis ” Development of scale-bridging methodologies and algorithms founded on the outcome of detailed atomistic simulations for the reliable prediction of the viscoelastic properties of polymer melts”, supervised by Prof. Vlasis G. Mavrantzas.

Awards-honors-fellowships

  • Top of Class Award for Undergraduate studies, State Scholarship Foundation, annually 2001 – 2006.
  • Top of Class Award for Undergraduate studies for the academic year 2003-2004, Technical Chamber of Greece, 2007.
  • Top of Class Award for excellence in Undergraduate studies, Technical Chamber of Greece, 2008.
  • Marie Curie Reintegration grant, European Commission, (FP7-PEOPLE-2011-CIG, Code 293945), 08/2011-07/2012 [Terminated as it was not possible to have it funded simultaneously with ΔΙΔΑΚΤΩΡ/0311/40].
  • National post-doctoral grant, Cyprus Research Promotion Foundation (ΔΙΔΑΚΤΩΡ/0311/40), 07/2012-12/2014.
  • Swiss Government Excellence Scholarship for Foreign Scholars, 01/09/2015-31/08/2016 (ESKAS No. 2015.0297).
  • Cyprus Research Award – “Young Researcher” 2015 (Thematic Area: Physical Sciences and Engineering), November 2015, https://www.youtube.com/watch?v=SX1OC-xs9zA (in Greek).
  • National grant, Cyprus Research Promotion Foundation (made available through the Cyprus Research Award – “Young Researcher” 2015) (ΚΟΥΛΤΟΥΡΑ/ΒΡ-ΝΕ/0415/01), 09/2016-03/2018.

Professional activities

  • Member of Hellenic Society of Rheology (HSR), European Society of Rheology (ESR), and Society of Rheology (SOR).
  • Reviewer for Physical Review Letters (PRL), Langmuir, Soft Matter, Journal of Rheology, Journal of Chemical Physics, Industrial and Engineering Chemistry Research, Powder Technology, Chemical Physics Letters, Physical Review E, Journal of Non-Newtonian Fluid Mechanics, and Macromolecular Theory and Simulation.