[Zurück]

D. Toneian, R. Blaak, G. Kahl, C. N. Likos:
"Magnetically Functionalized Star Polymers in Equilibrium and under Shear";
Poster: 10th Liquid Matter Conference (2017), Ljubljana; 17.07.2017 - 21.07.2017.

Star polymers are macromolecules consisting of a central site, attached to which are a
number f of linear polymer chains, called "arms". Depending on the chemical compo-
sition of the arms, the polymer stars exhibit intriguing features, both in isolation and in
concentrated solution. If, for example, one makes the fraction α of the polymers closest
to the central site of each arm solvophilic, and the remainder of the arm solvophobic,
one finds in computer simulations that the solvophobic parts aggregate into patches, the
number of which per polymer star is determined by f and α. These so called telechelic
star polymers can connect to one another via their patches, resulting in aggregate crys-
tals. The stability of the crystal lattice (e.g. diamond or simple cubic) is dependent on the
coordination number, i.e. the number of patches per star, and as such ultimately by f , α,
and the solvent quality. [1]
While one may be able to manipulate the latter parameter in an experiment, the function-
ality f and the solvophilic arm fraction α are set during synthesis of the star polymers,
and as such cannot be changed in-situ. To provide an additional, versatile avenue by
which one can control the inter-star interactions, we study in this work an alternative type
of star polymers: Instead of triggering aggregation of parts of the stars via solvophobicity,
we perform computer simulations of stars where each arm is homogeneous, except for
the free ends of the arms, which carry super-paramagnetic dipole moments. This way,
one can employ fine-grained control of the attraction of the arms´ ends by applying an
external magnetic field, the magnitude of which controls the interaction strength of the
dipoles. The direction of the external field plays an important role in the case where we
impose external shear flows of varying shear rates on the system.
We use Multiparticle Collision Dynamics (MPC) simulations [2, 3] to efficiently model the
explicit solute and allow for hydrodynamic interactions, and couple MPC to a Molecu-
lar Dynamics (MD) treatment of a coarse-grained model of the star polymers, the con-
stituents of the polymer chains being represented as a number N of effective monomers.
This approach allows us to scan parameter space and examine static and dynamic prop-
erties of dilute solutions, such as the number of patches, their alignment with the shear
flow direction, measures of the shape of the overall star, and relaxation times. We present
and interpret the data gathered, and discuss implications for possible applications, such
as tunable mixers in microfluidic devices.
[1] B. Capone, I. Coluzza, F. LoVerso, C. N. Likos, R. Blaak, Phys. Rev. Lett. 109, 238301
(2012).
[2] A. Malevanets and R. Kapral, J. Chem. Phys. 110, 8605 (1999).
[3] G. Gompper, T. Ihle, D. M. Kroll, and R. G. Winkler, Adv. Polym. Sci. 221, 1 (2009).

Projektleitung Gerhard Kahl:
DFS