Appl. Phys. A 74 [Suppl.], S361–S363 (2002) / Digital Object Identifier (DOI) 10.1007/s003390201627 Applied Physics A Materials Science & Processing Self and collective dynamics of ordered star polymer solutions J. Stellbrink 1, ∗ , J. Allgaier 1 , M. Monkenbusch 1 , D. Richter 1 , G. Ehlers 2 , P. Schleger 2 1 Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany 2 Institute Laue Langevin, Avenue des Martyrs, BP156, 38042 Grenoble, France Received: 18 July 2001/Accepted: 11 December 2001 –  Springer-Verlag 2002 Abstract. We investigated the dynamics of 18-arm poly- isoprene star polymer solutions well above their overlap concentration c ∗ . Combining neutron spin echo spectroscopy (NSE) and selective H/D labelling, we were able to separate inter- (collective) and intra-star (self ) dynamics. Only at low Q-vectors do self and collective dynamics become dis- cernible. Here, collective dynamics are found to be consistent with a colloidal approach resulting from star–star interac- tions. The collective short time diffusion coefficient D eff is well described by the term D 0 /S( Q), with D 0 the diffusion coefficient at infinite dilution. At Q m , the peak position in the structure factor S( Q), no difference is observable between collective and self dynamics. For covering the slowed-down dynamics at Q m the time range of NSE was extended for the first time up to 350 ns using long wavelengths, λ = 19 Å, at IN15 (ILL, Grenoble). We found that S( Q, t)/S( Q, 0) relaxes into a concentration-dependent plateau. The plateau height gives the mean-square displacement < r 2 > 1/2 of star cores, which is related to the blob size ξ of the surrounding star polymer solution obtained by dynamic light scattering. PACS: 83.10Nn; 31.10Pp; 61.25Hq Star polymers, i.e. f monodisperse linear polymer chains tethered to a central microscopic core, can actually be viewed as hybrids between polymer-like entities and colloidal par- ticles [1]. In solution star polymers show ordering phenom- ena as known from hard spheres [2], but opposite to those, star polymers start to interpenetrate at the overlap concen- tration c ∗ . The structure factor S( Q) of star polymer solutions could be described starting from a microscopic pair poten- tial [3], but, however, the dynamics are far less understood [4, 5]. Recently we started to investigate the microscopic dy- namics of ordered star polymer solutions by neutron spin echo spectroscopy (NSE) [6]. We found that at Q m , the peak ∗ Corresponding author. (Fax: +49-2461/61-2610, E-mail: j.stellbrink@fz-juelich.de) position in S( Q), the collective intermediate scattering func- tion S( Q, t)/S( Q, 0) relaxes into a concentration dependent plateau, indicating a constrained motion of star cores. Here, we report a continuation of this study to separate between inter- (collective) an intra-star (self ) dynamics by selective H/D-labelling. 1 Experimental Polyisoprene (PI) star polymers were prepared following an established procedure [7]. Living polymer chains prepared by anionic polymerisation were coupled to the linking agent octadeca-chlorosilane. The result of the synthesis are 18- arm star polymers with a near-monodisperse distribution in functionality and molecular weight [7], see Table 1. Whereas the first star polymer consists of protonated monomers near the core (scattering length density  = 2.68 × 10 9 cm −2 ) and deuterated in the shell ( = 7.00 × 10 10 cm −2 ), the second one is completely deuterated. Using deuterated methylcyclo- hexane, C 7 D 14 (99.8% D,  = 6.61 × 10 10 cm −2 ), solvent and deuterated monomers are contrast matched and in the experi- ment only the protonated monomers near the core are visible. NSE experiments were performed either at the new NSE instrument in Jülich [8], λ = 8 Å, 0.04 ≤ Q ≤ 0.2Å −1 , 1 ≤ τ ≤ 25 ns, or at IN15, ILL, λ = 8, 14, 19 Å, 0.02 ≤ Q ≤ 0.2Å −1 , 1 ≤ τ ≤ 348 ns (IN15 is a joined project of FZ Jülich, HMI Berlin and ILL, specially designed for long neu- tron wavelengths [9]). Table 1. Molecular characteristics of PI star polymers sample f N arm p M w /M n R g [Å] φ a) d [%] dh-S18 18 113 1.01 37.5 b) 75.4 d-S18 18 110 1.02 67.0 100 a) degree of deuteration, b) for the protonated core