Athanassios Z. Panagiotopoulos

Susan Dod Brown Professor of Chemical and Biological Engineering
Chair, Department of Chemical and Biological Engineering
Phone: 
609-258-4591
Email Address: 
azp@Princeton.EDU
Assistant: 
Office Location: 
A217 Engineering Quad
Degrees: 

Ph.D., Massachusetts Institute of Technology, 1986

Dipl. Eng., National Technical University of Athens, 1982

Honors and Awards

  • Robert L. Pigford Memorial Lecturer, U. of Delaware, 2018
  • Keith E. Gubbins Inaugural Lecturer, N. Carolina State U., 2016
  • Fellow, American Institute of Chemical Engineers, 2014
  • Chemical Engineering Distinguished Lecturer, Texas A&M at Qatar, 2013
  • American Academy of Arts and Sciences, 2012
  • National Academy of Engineering, 2004
  • J.M. Prausnitz Award in Applied Chemical Thermodynamics, 1998
  • Allan P. Colburn Award, American Institute of Chemical Engineers, 1995
  • Teacher-Scholar Award, Camille and Henry Dreyfus Foundation, 1992
  • Presidential Young Investigator, National Science Foundation, 1989
  • Postdoctoral Scholar, University of Oxford, 1986-87

Affiliations

  • Associated Faculty, Princeton Institute for Computational Science and Engineering
  • Associated Faculty, Princeton Institute for the Science and Technology of Materials

Research Interests

Research in our group focuses on development and application of theoretical and computer simulation techniques for the study of properties of fluids and materials. Emphasis is on molecular-based models that explicitly represent the main interactions among microscopic constituents of a system. These models can be used to predict the behavior of materials at conditions inaccessible to experiment and to gain a fundamental understanding of the microscopic basis for the observed macroscopic properties.  Our work usually requires large-scale numerical calculations involving a number of powerful molecular simulation methodologies. An example of such a methodology is Gibbs ensemble Monte Carlo, which provides a direct way to obtain coexistence properties of fluids from a single simulation.

Polymers under non-equilibrium conditions. The group is interested in developing methods for the study of properties of polymers under non-equilibrium conditions. We have investigated the formation of structures in colloid/polymer mixtures under strong flow conditions (see image below). Nonequilibrium molecular dynamics simulations have been used to investigate the influence of hydrodynamic interactions on vertical segregation (stratification) in drying mixtures of long and short polymer chains. In agreement with previous computer simulations and theoretical modeling, the short polymers stratify above the long polymers at the top of the drying film when hydrodynamic interactions between polymers are neglected. However, no stratification occurs under the same drying conditions when hydrodynamic interactions are incorporated through an explicit solvent model. We have also used a multi-scale approach which combines molecular dynamics and kinetic Monte Carlo simulations, to study a simple and scalable method for fabricating charge-stabilized polymer nanoparticles formed through a rapid solvent exchange. 

Polymers under non-equilibrium conditions

Image from Howard et al., Phys. Rev. Fluids 1 (4), 044203 (2016)

Self-assembly of nanoparticles. We are interested in the basic mechanisms of self-assembly in nanoparticle systems under both equilibrium and non-equilibrium conditions. We are determining the influence of interactions on the thermodynamics and kinetics of nanoparticle crystal phases, with special interest in open structures. As an example of non-equilibrium self-assembly, we have recently used molecular dynamics simulations of the epitaxial growth of high quality crystalline films for photonics applications from triblock Janus colloids. With a featureless substrate, the film morphologies had two stacking polymorphs appearing in nearly equal proportion. However, with a patterned substrate deliberately designed to be easy to fabricate by standard photolithography techniques, both grain size and selectivity towards the photonically active polymorph were greatly improved. Lower particle flux led to higher quality crystals, while higher flux led to frustrated films with smaller crystalline domains – see figure.

snapshots from the lowest and highest flux simulations

Figure from Reinhart and Panagiotopoulos, J. Chem. Phys. 150: 014504 (2019), shows snapshots from the lowest and highest flux simulations for patterned (A and B) and flat (C and D) substrates. 

Properties and Models for Electrolyte Systems. Electrolyte systems play an important role in chemical engineering separations, and also in geochemical environments and for biophysics. The mean ionic activity coefficients quantify the deviation of salt chemical potential from ideal solution behavior; experimental measurements are available for many salts over broad ranges of concentration and temperature, but there have been practically no prior simulation studies of these quantities, because if sampling difficulties for explicit-solvent electrolyte solutions. We are developing new methods for determination of properties of aqueous electrolytes and using them to improve the models for water and ions, by incorporating polarizability in the intermolecular potential models. For example, we have recently used forward-flux-sampling and metadynamics methods to obtain insights on the nucleation rates and pathways for salt crystallization from supersaturated aqueous solutions and to compare different salt and water models with respect to their ability to describe experimental measurements, as shown in the figure. We are also exploring the properties of molten carbonate electrolytes, which have applications to high-temperature fuel cells that can be used to separate CO2 for carbon sequestration.

nucleation rate prediction

Figure from Jiang et al., J. Phys. Chem.149: 141102 (2018), shows significant improvement in the nucleation rate prediction when polarizable models are used. 

Publications List: 
  1. A. Z. Panagiotopoulos, "Direct determination of phase coexistence properties of fluids by Monte Carlo simulation in a new ensemble," Mol. Phys., 61: 813-826 (1987).
  2. J. C. Palmer, F. Martelli, Y. Liu, R. Car, A. Z. Panagiotopoulos, and P. G. Debenedetti, “Metastable Liquid–Liquid transition in a Molecular Model of Water,” Nature, 510: 385-388 (2014).
  3. N. Li, A. Nikoubashman, and A. Z. Panagiotopoulos, “Multi-scale simulations of polymeric nanoparticle aggregation during rapid solvent exchange,” J. Chem. Phys., 149: 084904 (2018).
  4. H. Jiang, P. G. Debenedetti, and A. Z. Panagiotopoulos, “Communication: Nucleation rates of supersaturated aqueous NaCl using a polarizable force field,” J. Chem. Phys., 149: 141102 (2018).
  5. W. F. Reinhart and A. Z. Panagiotopoulos “Directed assembly of photonic crystals through simple substrate patterning,” J. Chem. Phys. 150: 014504 (2019).