The bulk dynamics of a compositionally asymmetric diblock copolymer studied using dynamic light scattering
1 Condensed Matter Physics and Chemistry Department,
Risø National Laboratory, P.O. Box 49, DK-4000 Roskilde,
2 Fakultät für Physik und Geowissenschaften, Universität Leipzig, Linnéstr. 5, D-04103 Leipzig, Germany - Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic, Heyrovsky Sq. 2, CZ-16206 Prague, Czech Republic
Received 19 March 1999 and Received in final form 25 August 1999
We have studied the bulk dynamics of a compositionally asymmetric poly(ethylene propylene)-poly(dimethylsiloxane) (PEP-PDMS) diblock copolymer in a large temperature range both in the ordered and in the disordered state. The volume fraction of the PEP block is 0.22. Apart from the disordered state, the sample shows three ordered morphologies. Using dynamic light scattering, we have investigated the dynamics in all four phases and combined these results with those obtained using pulsed field gradient NMR. In the disordered state, we find--apart from the slow cluster mode--the heterogeneity mode related to the self-diffusion of single chains. The relaxation time of this mode, reduced by temperature and the zero-shear viscosity , , increases with temperature. In the cubic phase right below the ODT temperature, we observe two diffusive processes, and we attribute the faster one to the mutual diffusion of micelles and block copolymers not bound to micelles (``free chains'') through the PDMS matrix. The slower mode may either be due to the mutual diffusion of free chains and chains bound to PEP micelles or to the cooperative diffusion of micellar aggregates. In the non-cubic ordered state at intermediate temperatures, an additional weak diffusive mode is observed. The low-temperature ordered state is body-centered cubic, and here, only the mutual diffusion of micelles and free chains lies in our experimental time window.
61.41.+e Polymers, elastomers and plastics - 83.10.Nn Polymer dynamics - 87.64.Cc Scattering of visible, uv, and infrared radiation
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