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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 5pst ≤ 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).

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