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Archiv-Übersicht     Angebot Nr. 14555

Angebotsdatum: 8. April 2022
Art der Stelle: Doktorarbeit / Diplomarbeit
Fachgebiet: Physik > Angewandte Physik
Titel des Themas: Long-range repulsion in polymer melts: Does the Anti-Casimir effect exist ?

Institut: Institut Charles Sadron CNRS & Univ. de Strasbourg
Herr Joachim Wittmer
23 Rue du Loess
67034 Strasbourg
Tel.: +33 (0)3 88 41 40 55   Fax.: +33 (0)3 88 41 40 99
Homepage: http://https://www.ics-cnrs.unistra.fr/
E-Mail Kontakt: mail

Beschreibung: In quantum field theory, the Casimir effect is a physical force, acting on the macroscopic boundaries of a confined space, which arises from the quantum fluctuations of the field. Named after the Dutch physicist Hendrik Casimir, who introduced the effect in 1948 focusing on electromagnetic systems, it is closely related to the London–van der Waals force which can be formulated on the same footing. Importantly, the (generalized) Casimir forces as the other (classical) contributions to the van der Waals force are always attractive which leads, e.g., to the well-known aggregation of small colloidal particles in solvents. Interestingly, recent theoretical work of our research group at the Institut Charles Sadron in Strasbourg suggests that universal long-range interactions exist in dense solutions and melts of linear polymer that are directly opposite to the van der Waals attraction and it was argued that this Anti-Casimir effect may increase the stability of colloids in dense polymer solutions [1].

Methoden: As one important consequence it was found that the pair correlation function of all monomers of the melt should follow at large distances a power law [1], rather than the exponential decay predicted by Edwards based on Flory's ideality hypothesis [2], and a corresponding relation in reciprocal space for the (experimentally relevant) total structure factor. In the first part of the proposed PhD project we shall attempt to demonstrate numerically the existence and relevance of the Anti-Casimir effect for equilibrium polymer systems with and without closed loops by means of the Monte Carlo simulations of the bond-fluctuation model using soft monomers and allowing the chains to freely break and recombine [2].

The second part of the PhD will focus on the pressure difference of a polymer melt confined in a thin slit of width H in grand-canonical contact with a large reservoir. While for equilibrium polymer melts with loops the density and pressure differences inside and outside the slit must vanish they should become finite for linear chain systems according to theory. We shall investigate the predictions for soft equilibrium polymers (with and without closed loops) by means of the LAMMPS programming environment [3].

In a nutshell: Motivated by recent polymer field theoretical work we suggest a mainly computational PhD study on equilibrium polymer melts with soft excluded volume.
Anfangsdatum: 1. Oktober 2022
Geschätzte Dauer: 3 years
Bezahlung: salaire brut" is 2135 Euro, the "salaire
Papers: [1] S.P. Obukov, A.N. Semenov, PRL, 95, 038305 (2005)
[2] J.P. Wittmer et al., J. Stat. Phys., 145, 1017-1126 (2011)
[3] S. J. Plimpton, J. Comp. Phys., 117, 1 (1995)
Sonstiges: To obtain the funding from the "Ecole Doctorale ED182" of the Strasbourg University interested candidates must present themself with a short motivation speech in front of a jury. We would in a first step select one promising candidate and invite him/her to the ICS to prepare this talk. At least this would be the normal procedure. Due to the covid pandemia all this may happen per "viscioconference" (online).