Neutron spin echo investigation of the concentration fluctuation dynamics in melts of diblock copolymers

Abstract

Diblock copolymers in the melt exhibit order-disorder phase transitions ͑ODT͒, which are accompanied by strong concentration fluctuations. These transitions are generally described in terms of the random phase approximation ͑RPA͒ of Leibler and Fredrickson, which is able to explain small angle scattering results in the neighborhood of the ODT, in particular around the correlation peak at q*. The RPA theory has been extended to include dynamical phenomena, predicting the short time relaxation of the dynamic structure factor in polymeric multicomponent systems. We report small angle neutron scattering and neutron spin echo experiments on polyethyleneblock-polyethylethylene ͑PE-PEE͒ and poly͑ethylene-propylene͒-block-polyethylethylene ͑PEP-PEE͒ copolymers with molecular weights of 16.500 and 68.000 g/mol, which explore the structure and dynamics of these block copolymers. Studying melts with different hydrogen/ deuterium labeling it was possible to observe experimentally the different relaxation modes of such systems separately. In particular the collective relaxation behavior as well as the single chain motion were accessed. The experimental results were quantitatively compared with the RPA predictions, which were based solely on the dynamical properties of the corresponding homopolymers and the static structure factors. The collective dynamics exhibits an unanticipated fast relaxation mode. This mode is most visible at low wave numbers (qуq*) but extends to length scales considerably shorter than the radius of gyration. Furthermore, the dynamical RPA yields expressions for the mobilities of chain segments in the block copolymer melt. These combination rules are at variance with the experimental findings for the single chain dynamics, while they hold for the collective response.

Polymer dynamics from large to small scales

“…2 displays experiments on polyethylethylene (PEE) (Montes et al, 1999) (PEE is obtained by hydrogenation from anionically synthesized 1-2 polybutadiene), where this prediction was tested. Experiments at different momentum transfers were superimposed according to equation 5.…”

Experimental aspects of polymer dynamics

“…In our presentation of neutron results on the dynamics of a polymer we restrict ourselves to the dynamics of linear polymer melts and omit the large number of experiments on solutions, on branched polymers like stars30 block copolymers,31 etc. In melts, the space–time frame of quasielastic scattering encompasses polymer motions on very short scales (side‐group, single bond) to, in favourable cases, global chain dimension.…”

“…Figure 4 displays experiments on polyethylethylene (PEE)31 (PEE is obtained by hydrogenation of anionically synthesized 1,2‐polybutadiene), where this prediction was tested. Experiments at different momentum transfers were superimposed according to Eqn.…”

Polymer Dynamics in Block Copolymer Electrolytes Detected by Neutron Spin Echo

“…Previous studies on these systems using NSE are limited to the Rouse regime ( t ≤ 20 ns). 14,17,33 Previous studies on nanostructured block copolymer electrolytes are limited to studying the cooperative grain dynamics on the 10 -2 -10 2 s timescale. 34 The block copolymer electrolyte of interest is a well-studied model system: , were 0, 0.025, 0.075, and 0.10.…”