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 melts at interfaces

Understanding the fascinating and complex dynamics of melts of large flexible polymer coils close to solid substrates has been an ongoing challenge for many decades. From the point of view of molecular simulations, the spectrum of length and time scales associated with polymer melts of long chains poses a formidable challenge to studying the long-time dynamics.

We have formulated a method, based on combining self-consistent field theory with dynamically corrected transition state theory, for estimating the rates of adsorption and desorption of end-constrained chains e.g., by cross-links or entanglements) from a polymer melt onto a solid substrate. This approach has been successfully applied on a polyethylene/graphite system, where the whole methodology was parameterized by atomistically detailed molecular simulations. For short-chain melts, which can still be addressed by molecular dynamics simulations with reasonable computational resources, the self-consistent field approach gives predictions of the adsorption and desorption rate constants which are gratifyingly close to molecular dynamics estimates.


Figure 1: Schematic illustration of an end-constrained subchain of 50 CH2 units (marked in red), whose residence times in the adsorbed and desorbed state, in the course of an MD simulation, were used for estimating adsorption and desorption kinetics via hazard-plot analysis. External link: http://pubs.acs.org/doi/abs/10.1021/ma501454t

To the best of our knowledge, this the first time that the solution of the polymer SCF problem next to a solid surface has been used to provide insight into the dynamics of the system. This work suggests that SCF, coupled with transition-state theory, can give good results for the rate of adsorption/ desorption between polymers in a melt and a surface. SCF theory is less computationally demanding than atomistic simulations, and thus SCF can be used to examine regimes not practically accessible to atomistic simulations, such as the regimes of low adsorption or low desorption rates. Furthermore, the parameters in SCF have been directly connected to atomistic parameters, suggesting that SCF may provide a more faithful description of the problem than alternative, coarse-grained simulation methods. In the regime where molecular dynamics simulation of adsorption rates is practical (short chains, very close to the surface), our results for the adsorption rate are in good agreement with the results from molecular dynamics simulation. Finally, a reasonable agreement between the melt adhesion tension computed from SCF and that measured in atomistic simulations and in experiment, was found.


Figure 2: Adsorption rate constant, predicted by Self Consistent Field / Transition State Theory calculations, is presented as a function of the distance of the ends of an end-constrained subchain from the graphite surface. Both ends are kept at the same distance from the graphite surface, and we consider chain lengths of N = 50 and N = 100 methylenes. Adsorption rates for an end-constrained C50 subchain in a C200 polyethylene melt next to graphite obtained by MD simulation using a detailed united-atom model are also shown. External link: http://pubs.acs.org/doi/abs/10.1021/ma501454t

Relevant publications

[1] Daoulas, K. C.; Theodorou, D. N.; Harmandaris, V. A.; Karayiannis, N. C.; Mavrantzas, V. G. "Self-Consistent-Field Study of Compressible Semiflexible Melts Adsorbed on a Solid Substrate and Comparison with Atomistic Simulations" Macromolecules 2005, 38, 7134-7149.
http://pubs.acs.org/doi/abs/10.1021/ma050218b
[2] Theodorou, D. N.; Vogiatzis, G. G.; Kritikos, G. "Self-Consistent-Field Study of Adsorption and Desorption Kinetics of Polyethylene Melts on Graphite and Comparison with Atomistic Simulations" Macromolecules 2014, 47, 6964-6981.
http://pubs.acs.org/doi/abs/10.1021/ma501454t
[3] Kritikos, G.; Sgouros, A.P.; Vogiatzis, G.G.; Theodorou, D.N. "Molecular Dynamics Study of Polyethylene under Extreme Confinement" Journal of Physics: Conference Series 2016, 738.
http://dx.doi.org/10.1088/1742-6596/738/1/012012
[4] Sgouros, A.P.; Vogiatzis, G.G.; Kritikos, G.; Boziki, A.; Nikolakopoulou, A.; Liveris, D.; Theodorou, D.N. "Molecular simulations of free and graphite capped polyethylene films" Macromolecules 2017, 50, 8827-8844.
http://dx.doi.org/10.1021/acs.macromol.7b01808


Relevant projects

[1] 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/
[2] "Multiscale Simulations of Complex Polymer Systems" (MuSiComPS), Limmat Foundation, Zurich, Switzerland.