An experimental approach to the molecular viscoelasticity of bulk polymers by spectroscopic techniques: neutron scattering, infrared dichroism and fluorescence polarization

Abstract

Small-angle neutron scattering (s.a.n.s.), infrared dichroism (i.r.d.) and fluorescence polarization (f.p.) are techniques which provide information on the molecular orientation of stretched polymers; they can thus be used to study the viscoelastic behaviour of bulk polymers on a molecular scale.

The basic principles, the experimental requirements and the molecular parameters available from experiments are described for each technique. Thus s.a.n.s. leads to overall dimensions of deuterated chains in a mixture of deuterated and hydrogenated polymers. In contrast, i.r.d. yields the chain segment orientation averaged over all the chains of the sample, whereas orientation determined from f.p. only deals with labelled sequences (central or end sequences) of labelled chains mixed with normal chains.

Experimental results obtained by i.r.d. and f.p. on polystyrene samples stretched at a constant strain rate above T_g are discussed. The influence of the molecular weight of either labelled chains or polymer matrices leads us to consider first a topological coupling between the relaxation processes of the labelled chain and those of the surrounding chains and secondly an orientation effect arising from the anisotropy of the strained polymer medium.

An i.r.d. study of the orientation of compatible blends of polystyrene and poly(2,6-dimethyl-1,4-phenylene oxide) is reported. Each polymer component exhibits different orientation behaviour.