Bayreuth 1998 – scientific programme
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PO: Polymerphysik
PO 1: Molekulare Dynamik
PO 1.2: Talk
Tuesday, March 10, 1998, 16:45–17:05, H17
Entanglement effects on the microscopic dynamics of concentrated star polymer solutions investigated by neutron spin echo spectroscopy — •J. Stellbrink, J. Allgaier, M. Monkenbusch, and D. Richter — IFF, Forschungzentrum Jülich, D-52425 Jülich
Neutron spin echo spectroscopy (NSE), a high resolution quasi-elastic
scattering method, allows the investigation of dynamical processes
on microscopic time and length scales.
NSE measures directly the intermediate scattering function S(Q,t) in the
range 5ps ≤ t ≤ 40ns and r ≈ 10 Å.
The recently developed new NSE instrument at the FRJ-2 in J"ulich was used
for studying the effects of intra- and intermolecular entanglements on
the microscopic dynamics of star polymer solutions well below and above
the overlap concentration c*.
We found a pronounced minimum of the reduced relaxation
frequency Γ/Q3 as a function of scattering vector Q.
Whereas in dilute solution this minimum arises from the nonuniform density
distribution inside one star polymer,
above c* the position of the minimum scales with the peak
position of the static structure factor S(Q), i.e. is due to
intermolecular interactions causing a liquid like order.
This phenomenon resembles the deGennes-narrowing known
from simple liquids.
Moreover, the obtained NSE results are discussed in the context of an expected
structural glass transition of star polymer solutions, as recently
found by dynamic light scattering1).
Both results emphasize the
importance of star polymers as
hybrids between polymer and colloid like entities
thereby connecting these two areas of research.
1) J.Stellbrink, J. Allgaier and D. Richter; Phys. Rev. E, 56, 3772
(1997).