Understanding the stiffness of Macromolecules: From single chains to semi flexible polymer brushes
DIPC Seminars
- Speaker
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Kurt Binder (Institut fuer Physik, Johannes Gutenberg Universitaet, Mainz, Germany)
- When
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2015/09/30
13:00 - Place
- Donostia International Physics Center
- Add to calendar
-
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Professor Kurt Binder
Institut fuer Physik,Johannes Gutenberg Universitaet Mainz
55099 Mainz,Staudinger Weg 9,Germany
ABSTRACT
The key parameter to characterize the stiffness of polymers is their
persistence length. Unfortunately,there is confusion in the literature on the
proper definition of this length: Using the decay constant of an exponentially
decaying orientation correlation of bonds along the chain contour works only
for "phantom chainsâ€. For real macromolecules in the long chain limit the
decay is always a power law (with an exponent 3/2 for chains in the melt or
Theta solutions,and an exponent related to the Flory exponent for polymers in
dilute solutions under good solvent conditions).The validity of the Kratky-
Porod model for chain extensions of semiflexible chains hence also is
restricted (it fails in d=2 dimensions,a case relevant for adsorbed DNA,apart
from the trivial rod-like regime ; in d=3 Gaussian behavior occurs only for a
intermediate range of chain lengths).These results are exemplified by
extensive Monte Carlo simulations of a lattice model using the pruned-enriched
Rosenbluth method(PERM).
A subtle problem is the extension of these concepts to "bottlebrush
polymers",where flexible chains are grafted to a (flexible) backbone,and thus
(on a coarse-grained level) a wormlike chain results.The dependence of the
persistence length on the side chain length will be clarified,discussing also
pertinent experiments.Finally,also the effects of chain stiffness for standard
polymer brushes (where macromolecules are densely grafted by one chain end to
a planar substrate) will be discussed,and evidence for a new kind of phase
transition in compressed semiflexible polymer brushes is given.