Research

Current projects

(Poly)electrolyte solvation (2016-current)

The traditional modeling of electrolyte and polyelectrolyte solutions rely mostly on the “primitive model” of ionic solutions where all charged species are treated explicitly as charged hard spheres and the solvent enters the model through its influence on the permittivity of the continuous medium surrounding the charged species. We demonstrate that treatment of the solvent as a continuum medium neglects both the solvation of the ions and the polymeric species, which can have a crucial role in the structural properties of the polyelectrolyte solutions. We find that solvation influences many thermodynamic and dynamic solution properties that are important for biological applications and ion conductivity for energy storage applications.

Heterogeneous structure formation in a polyelectrolyte solution; polyelectrolyte chains (red), counter-ions (blue), solvent is rendered invisible.
Disappearance of the polyelectrolyte peak in salt-free solutions, Physical Review E 102, 012611 (2020)Polyelectrolyte association and solvation, A. Chremos, J. F. Douglas, J. Chem. Phys. 149, 163305 (2018).Competitive solvation effects in polyelectrolyte solutions, A. Chremos, J. F. Douglas, ACS Books, ACS Symposium Series 1296 Chapter 2, pp 15 (2018).Influence of ion solvation on the properties of electrolyte solutions, M. Andreev, J. de Pablo, A. Chremos, J. F. Douglas, J. Phys. Chem. B 122, 4029 (2018).Coarse-Grained Model of the Dynamics of Electrolyte Solutions, M. Andreev, A. Chremos, J. de Pablo, J. F. Douglas, J. Phys. Chem. B 121, 8195 (2017).Communication: Counter-ion solvation and anomalous low-angle scattering in salt-free polyelectrolyte solutions, A. Chremos, J. F. Douglas, J. Chem. Phys. 147, 241103 (2017).Influence of higher valent ions on flexible polyelectrolyte stiffness and counter-ion distribution, A. Chremos, and J. F. Douglas, J. Chem. Phys. 144, 164904 (2016).Counter-ion distribution around flexible polyelectrolytes having different molecular architecture, A. Chremos and J. F. Douglas, Soft Matter 12, 2932 (2016).

Molecular architecture in polymer melts (2012-current)

Variation of molecular topology offers new venues for designing materials with optimal properties, which has immediate relevance to many applications, e.g., as polymer membranes to control rates of ion transfer in batteries. For specific molecular structures (e.g., linear chains) there are well established theoretical frameworks to describe and predict their behavior. However, we still lack a fundamental understanding of the structure-property relations as the molecular structure deviates from the ideal molecular structures that theories are built on.

Bead-spring model of bottlebrush polymer.
A Comparative Study of Thermodynamic, Conformational, and Structural Properties of Bottlebrush with Star and Ring Polymer Melts, A. Chremos, J. F. Douglas, J. Chem. Phys. 149, 044904 (2018).Influence of polymer architectures on diffusion in unentangled polymer melts, A. Chremos, C. Jeong, and J. F. Douglas, Soft matter 13, 5778 (2017).Communication: When does a branched polymer become a particle?, A. Chremos and J. F. Douglas, J. Chem. Phys. 143, 111104 (2015).Structure and dynamical intra-molecular heterogeneity of star polymer melts above glass transition temperature, A. Chremos, E. Glynos, and P. F. Green, J. Chem. Phys. 142, 044901 (2015).

Machine Learning for the multi-parameter model optimization (2018-current)

Recent advances in machine learning (ML) have allowed for a significant acceleration in the pace of discovery using data-driven paradigms, i.e., efficient and effective methods to generate, manage, and utilize relevant information. The goal is the development of a ML framework that would allow the description and prediction of both the thermodynamic and dynamic properties for simple and complex fluids in a self-consistent way, thus increasing the speed and reducing the cost of having a high-fidelity global representation of the thermodynamic properties and dynamic properties of fluids and their mixtures.

Past projects

Thin films of block copolymers under shear (2009-2012)

Current manufacturing (lithography) techniques cannot mass-provide patterns below the 16 nm threshold due to increasingly high energy and economic costs. A promising alternative is to manipulate matter via self-assembly, though there are still problems of robustness and controlling self-assembly process at nanometer scale. My work at Princeton University was focused on understanding how steady shear influences the morphologies of thin films of diblock copolymers. Above a critical shear rate and below the order-disorder transition, the sphere-forming thin films have their spherical domains melted and reform into cylindrical domains having an orientation parallel to the shear direction. A coarse-grained model is developed allowing the description of these polymers away from equilibrium; a feature not captured in mean field type theories and models. Moreover, we were able to identify the conditions for log-rolling behavior.

Comparison between simulations and experimental images.
Ultra thin films of diblock copolymers under shear, A. Chremos, K. Margaritis, A. Z. Panagiotopoulos, Soft Matter 6, 3588 (2010).Shear-induced alignment of lamellae in thin films of diblock copolymers, A. Chremos, P. M. Chaikin, R. A. Register, A. Z. Panagiotopoulos, Soft Matter 8, 7803 (2012).Sphere-to-cylinder transitions in thin films of diblock copolymers under shear: the role of wetting layers, A. Chremos, P. M. Chaikin, R. A. Register, and A. Z. Panagiotopoulos, Macromolecules 45, 4406 (2012).

Polymer-grafted nanoparticles in solvent-free conditions (2010-2017)

Nanoparticle ionic materials (NIMs) and nanoparticle organic hybrid materials (NOHMs) are organic-inorganic hybrid materials composed by a nanoparticle core functionalized with a covalently tethered (ionic in the case of NIMs) corona. Their flow properties in the absence of solvent range from glassy solids to free flowing liquids and show promising use in carbon capture, energy capture and storage, as well as water purification. The aim was to develop suitable coarse-grained models for gaining insights on the structural and dynamical properties of polymer-grafted nanoparticles in solvent-free conditions. Novel temperature-depended structural behavior maps that predict under what molecular parameters (e.g., core size and grafting density) a structural behavior is anticipated, e.g., anisotropic aggregation or a reverse thermal vitrification were constructed. Unlike conventional materials, we found that the fluid properties can be tuned by the variation of the geometric properties alone.

Morphology diagram of polymer-grafted nanoparticles in the absence of solvent.
Particle localization and hyperuniformity of polymer‐grafted nanoparticle materials, A. Chremos, J. F. Douglas, Annalen der Physik 529, 1600342 (2017).Self-assembly of polymer-grafted nanoparticles in solvent-free conditions, A. Chremos and J. F. Douglas, Soft matter 12, 9527 (2016).Dynamics in coarse-grained models for oligomer-grafted silica nanoparticles, B. Hong, A. Chremos, A. Z. Panagiotopoulos, J. Chem. Phys. 136, 204904 (2012).Dynamics of solvent-free grafted nanoparticles, A. Chremos, A. Z. Panagiotopoulos, and D. L. Koch, J. Chem. Phys. 136, 044902 (2012).Simulations of the structure and dynamics of nanoparticle-based ionic liquids, B. Hong, A. Chremos, and A. Z. Panagiotopoulos, Faraday Discussions 154, 29 (2012).Structure of solvent-free grafted nanoparticles: Molecular dynamics and density-functional theory, A. Chremos, A. Z. Panagiotopoulos, H. Y. Yu, and D. L. Koch, J. Chem. Phys. 135, 114901 (2011).Structural Transitions of Solvent-Free Oligomer-Grafted Nanoparticles, A. Chremos and A. Z. Panagiotopoulos, Phys. Rev. Lett. 107, 105503 (2011).