[Zurück]

D. Toneian, R. Blaak, G. Kahl, C. N. Likos:
"Conformational and Dynamic Properties of Magnetic Star Polymers Under Shear";
Poster: NECD18 - Nonequibrilibium Collective Dynamics: Bridging the Gap between Hard and Soft Materials, Potsdam; 08.10.2018 - 11.10.2018.

We present computer simulations of magnetically functionalized star polymers and their
conformational and dynamic properties, with an emphasis on systems that are driven
out of equilibrium via externally applied shear flow. Hydrodynamic interactions are taken
into account via Multi-Particle Collision Dynamics (MPCD) [1], which is coupled to the
Molecular Dynamics (MD) simulation of the stars.
Star polymers are macromolecules that consist of a central core, to which one attaches
a number of linear polymer chains, called arms. Star polymers with different chemical
composition of the polymer arms can exhibit very different behavior in various scenarios;
in particular, self-assembly phenomena, both on the level of a single star and in the case
of numerous stars in dense solution, are sensitive to the way the polymer arms interact
with one another.
We propose a model where, instead of relying on e.g. hydrophobicity to drive self-
assembly [2], we decorate the free ends of the arms with super-paramagnetic particles.
In the presence of an external magnetic field, these particles develop a magnetic dipole
moment, the magnitude and orientation of which are well-defined functions of the external
field.
We discuss the dominant role the magnetic field plays for the conformational properties
of the star polymers in equilibrium [3]. We then demonstrate in non-equilibrium computer
simulations that the number of magnetic clusters, along with their orientation relative to
the shear flow direction and shear gradient direction, is of crucial importance for the ob-
served size and geometry; since there is a competition between the attractive interaction
of the super-paramagnetic dipoles and the shear-flow-induced stresses that try to tear
magnetic clusters apart, the strength of the applied magnetic field is also shown to be
of great influence. We consider further dynamic aspects of stars under shear, demon-
strating a strong dependence of e.g. rotational behavior on the strength and direction of
the external magnetic field, and briefly discuss future developments and hypotheses for
possible applications in drug delivery or tunable mixers in micro-fluidics.
[1] G. Gompper, T. Ihle, D. M. Kroll, and R. G. Winkler, Adv. Polym. Sci. 221, 1 (2009). [2]
B. Capone, I. Coluzza, F. LoVerso, C. N. Likos, R. Blaak, Phys. Rev. Lett. 109, 238301
(2012). [3] R. Blaak and C. N. Likos, Eur. Phys. J. E 41, 3 (2018).

Projektleitung Gerhard Kahl:
DFS