National Technical University of Athens
School of Chemical Engineering
Department of Materials Science and Engineering
Computational Materials Science and Engineering Group (Co.M.S.E.)
 
 
 
 
News

16-July-2018
Master thesis presentation: On the 17th of July 2018, Panagiotis Petris will present his Master Thesis, entitled "Thermodynamic Analysis of n-Hexane/Ethanol Binary Mixtures Using Kirkwood-Buff Theory" in front of his three-member examination committee. The presentation will take place in the "Nikos Koumoutsos" hall of the Chemical Engineering building at 16:00.
Click here for an abstract of the presentation!

29-June-2018
During July 2-5, the following group members: Aikaterini Galata, Nikolaos Evaggelou, Matrona Panou, Vasilios Papasimakopoulos and Evaggelos Konialidis, will defend their Diploma Thesis. Details regarding the presentations can be found in the news section.

13-June-2018
This Monday, 17th of June 2018, David will celebrate with us his 30+ birthday around 4 pm! Let's all be there!
(free cake/sweets will be served!!!)

18-May-2018
Next Thursday, 24th of May 2018, at 13:00, we will hold our group meeting in "Nikos Koumoutsos" room. Dr. David Nieto Simavilla will present his work "Changes in the thermal properties of polymeric materials induced by molecular orientation: Experimental methods, current understanding and strategies for the application to numerical methods".
Click here to download the abstract of the presentation.

15-May-2018
Warmest congratulations to our former group member and collaborator, Dr. Georgios Vogiatzis for receiving the EΛETY-GRACM Ph.D Award for the best thesis of the year 2015!
The award will be bestowed at the opening ceremony of the 9th GRACM 2018 International Congress on Computational Mechanics on 4-6 June at Chania, Crete.

4-May-2018
Next Thursday, 10th of May 2018, at 13:00, we will hold our group meeting in "Nikos Koumoutsos" room. Aikaterini Galata will present her recent work "Thermodynamic Analysis of Lennard-Jones Binary Mixtures Using Kirkwood-Buff Theory".
Click here to download the abstract of the presentation.

24-April-2018
Diploma thesis presentation: On the 30th of April 2018, Dora Argyropoulou will present her Diploma Thesis, entitled "Computational Study of the Effects of Tacticity on the Conformational Properties of Unperturbed Chains of Polypropylene Homopolymers and Ethylene-Propylene Copolymers" in front of her three-member examination committee. The presentation will take place in the "Nikos Koumoutsos" hall of the Chemical Engineering building at 13:00.
Click here for an abstract of the presentation!

5-April-2018
On the 27th of March 2018, Prof. Doros N. Theodorou, Ph.D. received the honor at DFYP 2018, the international conference on Deformation, Yield, and Fracture of Polymers, in Kerkrade, the Netherlands!
For more details go to the News section or to the official source!

16-March-2018
Ph.D. thesis presentation: On the 19th of March 2018, Orestis George Ziogos will present his Ph.D. Thesis, entitled "Multiscale Simulations of Discotic Materials" in front of his seven-member examination committee. The presentation will take place in the "Nikos Koumoutsos" hall of the Chemical Engineering building at 12:00.
Click here for an abstract of the talk




Read all news...
Polymer-matrix nanocomposites

Polymer-matrix nanocomposites, i.e. nanoparticle-filled polymers, offer huge potential for future applications and energy savings, and are considered as an important branch of the emerging field of nanotechnology. The observation that, other things being equal, the effectiveness of the filler increases with an increase in surface to volume ratio has provided large impetus for a shift from micron- to nanosized filler particles.


Figure 1: Levels of modeling developed for the study of polymer matrix nanocomposites, methods employed in each one and main simulation observables.

Four interconnected levels of representation have been developed for polymer-matrix nanocomposites (Figure 1):

(a) An atomistic one, where both nanoparticles and polymer chains are represented in terms of detailed atomistic force fields. Fullerenes (C60) are dispersed in PS matrix and atomistic Molecular Dynamics (MD) simulations are undertaken to uncover details of packing and to quantify (local and global) segmental dynamics and (atomic and local) stresses (Figure 2).


Figure 2: Quantification of many-particle influence on polymer dynamics via a Voronoi tessellation of the simulation box (left figure). Mean-square atomic displacements (MSD) of PS backbone carbon atoms as a function of time for pure PS and PS + 1% C60 (right-hand side figure). In the case of fullerene nanocomposites, an analysis of the dependence of backbone MSD on confinement is also presented for most and least confined Voronoi cells. External links: http://pubs.acs.org/doi/abs/10.1021/ma402214r, http://arxiv.org/abs/1401.4314

(b) A coarse-grained representation, in which each repeat unit is mapped onto a single "superatom", and each nanoparticle is viewed as a solid object interacting with the polymer superatoms and other nanoparticles via Hamaker-type potentials. Equilibration of coarse-grained polymer-nanoparticle systems at all length scales is achieved via connectivity-altering Monte Carlo (MC) moves. These simulations are important for generating well-equilibrated initial configurations for atomistic MD through reverse mapping.

(c) A Field Theory-inspired Monte Carlo (FT-i MC) level, where polymer chains are represented as freely jointed sequences of Kuhn segments. For polymer-polymer interactions, an effective energy function is used, which prevents large departures of the local polymer density from its value in the bulk melt everywhere in the system. This simulation methodology is capable of capturing structural features at length scales on the order of hundreds of nanometers. Brush thickness and scattering curves from the grafted PS corona of silica particles dispersed in PS have been predicted (Figure 3).


Figure 3: The calculated brush thickness (using two estimates indicated in the left figure) is plotted versus the square root of the degree of polymerization of grafted chains, Ng, times the fourth root of the grafting density, σ. Points correspond to systems containing an 8-nm-radius silica particle grafted with PS chains and dispersed in PS matrix. External links: http://pubs.acs.org/doi/abs/10.1021/ma400107q, http://arxiv.org/abs/1401.4001

(d) A slip-spring network representation where cross-links, entanglements and chain ends are the degrees of freedom of the polymeric matrix. From the thermodynamic point of view, the system under study is fully described by a Helmholtz energy function which accounts for the entropic springs connecting cross-links or entanglements, non-bonded interactions (derived from any appropriate equation of state, e.g. the Sanchez-Lacombe) and Hamaker interactions between nodal points - nanoparticles and nanoparticles - nanoparticles. Brownian simulations at this level, operating at the length scales of up to 1 μm and time scales up to 1 ms, account for changes in segmental mobility induced by the nanoparticles and track elementary events of chain slippage across entanglements, chain entanglement and re-entanglement.

Relevant publications

[1] Vogiatzis, G. G.; Voyiatzis, E.; Theodorou, D. N. "Monte Carlo simulations of a coarse grained model for an athermal all-polystyrene nanocomposite system" Eur. Polym. J. 2011, 47, 699-712.
http://dx.doi.org/10.1016/j.eurpolymj.2010.09.017, http://arxiv.org/abs/1401.3364
[2] Vogiatzis, G. G.; Theodorou, D. N. "Structure of Polymer Layers Grafted to Nanoparticles in Silica - Polystyrene Nanocomposites" Macromolecules 2013, 46, 4670-4683.
http://pubs.acs.org/doi/abs/10.1021/ma400107q, http://arxiv.org/abs/1401.4001
[3] Vogiatzis, G. G.; Theodorou, D. N. "Local Segmental Dynamics and Stresses in Polystyrene - C60 Mixtures" Macromolecules 2014, 47, 387-404.
http://pubs.acs.org/doi/abs/10.1021/ma402214r, http://arxiv.org/abs/1401.4314
[4] Mathioudakis, I.G.; Vogiatzis, G.G.; Tzoumanekas, C.; Theodorou, D.N. "Molecular Modeling and Simulation of Polymer Nanocomposites at Multiple Length Scales" IEEE Trans. Nanotechnol. 2016, 15, 416-422.
http://dx.doi.org/10.1109/TNANO.2016.2538460

Relevant projects

[1] EU NANOMODEL, Multi-scale modeling of nano-structured polymeric materials: from chemistry to materials performance.
http://cordis.europa.eu/project/rcn/88888_en.html
[2] EU COMPNANOCOMP, Multiscale computational approach to the design of polymer-matrix nanocomposites.
http://cordis.europa.eu/project/rcn/101278_en.html
http://www.compnanocomp.eu/