Anisotropy of a flexible polymeric chain in a nematic field : neutron scattering versus magnetic resonance

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Abstract
Flexible polymeric chains are dissolved in a nematic liquid crystal; the effect of the nematic field is probed through s.a.n.s. and 2H n.m.r. The orientational order for the segments of perdeuterated polystyrene (Mw = 2 100), dissolved in p-ethoxybenzilidene p-n butylaniline, is obtained from 2H n.m.r. spectra : this parameter has the same temperature dependence as the order parameter of the solvent. Yet s.a.n.s. experiments do not show an anisotropy of the overall dimensions of the same macromolecules dissolved in p-azoxy-anisole. This apparent conflict is resolved when the anisotropy of the radius of gyration is calculated as a function of the spherical harmonics which describe the averaged orientation of the segments