In our recent paper [1] we present numerical results and theoretical arguments,
demonstrating a non-exponential, long ranged decay of the bond-bond correlation
function P(s) as a function of the contour distance s.
Suggesting a profound analogy with the well-known long range
velocity correlations in liquids we find
P(s) to decay algebraically as s-3/2.
See the figure on the right.
As a consequence, the operational definition of the persistent length should be carefully revisited.
We have analysed in detail the polymer form factor F(q)
and the total structure factor S(q) in order to provide
experimental testing beds for our theoretical predicitions.
For instance, we show a strinking hump in the Kratky plot
representation of q2 F(q) which may be
visible in neutron scattering experiments of long
flexible polymers.
3. Polymer melts in ultrathin slits: Silberberg's hypothesis put to a test
Consistently, we find P(s) ~ 1/s for polymer melts in ultrathin
quasi two dimensional slits [2]. The confinement has a pronounced effect
on intra- and intermolecular correlations: the walls force a chain to
fold back into volume it pervades; this volume is thus gradually
depleted of other chains as the film thickness decreases.
The resulting reduction of chain interdigitation entails deviations from
ideal behavior (Silberberg's hypothesis). We study these deviations by
discussing mainly conformational properties (chain extension, intrachain
structure factor, etc.) of the polymer films. Our simulation results are
compared with a recent theoretical approach attempting to go beyond
Silberberg's hypothesis.
4. Fluctuation-induced long-range interactions in composite polymer systems
We also challenge the applicability of the so-called "Random Phase
Approximation" (A.N. Semenov and A. Johner [3]) for dense polymers.
There are fluctuation-induced universal long-range forces which have
the important consequence to counterbalance attractive van-der Waals
forces between two colloidal particles (of size much smaller than
that of a polymer coil). This should lead to a stabilization of the
dispersed particles in a polymer matrix consisting of long chains.
We propose to further explore this stabilization mechanism
theoretically and via computer simulations.
A.N. Semenov and S. Obukhov have also developed a theoretical approach
predicting polymer-induced repulsion between colloidal particles in
semidilute solutions [4,5].
Finding the optimal conditions for such polymer-induced colloidal
stabilization is another important goal inviting theoretical
investigations of the effects of concentration, molecular weight,
molecular weight distribution, solvent quality,
macromolecular architecture (linear, branched or other),
block-copolymer structure and polymer-colloid interactions
on the long-range forces.
5. Collaboration
J.P. Wittmer (principal investigator), H. Meyer, J. Baschnagel,
A. Johner, A.N. Semenov, S. Obukhov (Gainesville, USA),
M. Müller (Göttingen, Germany)
6. Related papers