G. Rossi (1), L. Monticelli (2), S. R. Puisto (3), N.
Rostedt (3), I. Vattulainen (4) and T. Ala-Nissilä (1)
(1) Department of Applied Physics, Aalto University
School of Science, P.O. Box 11000, 00076 Aalto, Espoo, Finland
(2) INSERM, UMR-S 665, DSIMB, 6 rue Alexander Cabanel,
75015 Paris, France
(3) MatOx Pembroke House, 36-37 Pembroke Street, Oxford
OX1 1BP, United Kingdom
(4) Department of Physics, Tampere University of
Technology, P.O. Box 692, FI-33101 Tampere, Finland
Optimization of polymer properties in industrial
applications is generally achieved by
controlling the fine details of their chemical composition,
often through expensive and
time-consuming trial-and-error procedures. Computer
modelling can speed up these
procedures by predicting changes in material properties as a
function of chemical
composition. Unfortunately, the classical simulations of
polymer melts from atomistic
detail are subject to stringent limitations to the time and
length scales of the
phenomena that can be observed.
Coarse-graining strategies can help to overcome these
limitations. Coarse-graining
involves grouping clusters of atoms into super-atoms, or
beads. Coarse-grained (CG)
models are computationally faster than atomistic ones thanks
to a reduction in the
number of degrees of freedom and the use of smoother
interaction potentials,
allowing for longer time step in molecular dynamics (MD)
simulations.
We introduce a new hybrid thermodynamic-structural approach
to the coarse-
graining of polymers. The new model is developed within the
framework of the
MARTINI force-field [Marrink et al., J. Phys. Chem. B, 2007,
111, 7812], which uses
mainly thermodynamic properties as targets in the
parameterization. Density and
structural properties of the polymer melt can be used to
refine the force-field
parameterization. We test our procedure on polystyrene [G.
Rossi et al., Soft Matter,
DOI:10.1039/C0SM00481B], a standard benchmark for
coarse-grained polymer
force-fields. Structural properties in the melt are well
reproduced, and their scaling
with chain length agrees with available experimental data.
The CG force-field shows
reasonable transferability between 350 and 600 K. The model
is computationally
efficient and polymer melts and solutions can be simulated
by MD over length scales
of tens of nanometers and time scales of tens of microseconds.
Two applications of polymer models developed within the
MARTINI framework are
shown. The first concerns the dynamics of polystyrene-C60
nanocomposites, a
system that has been shown to have unusual rheological and
mechanical properties.
The second application concerns a polyester resin, whose
mechanical properties are
investigated by means of non-equilibrium molecular dynamics
simulations.
Speaker:
Giulia Rossi
(Aalto University School of Science)