Neutron Scattering by Small Chainlike Molecules Dispersed in CS2

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Abstract
The energyspectra of neutronsscattered by dilute solutions of chainlike molecules can throw light on the various types of molecular movements. Such a scattering experiment has been carried out using two low molecular weight ( Z=3 and 9) polymers of the poly‐oxy‐ethylene type dissolved in CS2, as scattering samples. The quasielastic part of the energyspectra has been analyzed in terms of the motion of the center of mass and that of the chain segments. The variation with Z of the diffusion coefficient D (connected with the center of mass motion) indicates that the solvent—solute system interacts in the free draining limit. The constant a (related to the random motion of the chain segments) varies as q γ with the exponent γ increasing with Z. It is also found that in both the cases studied, the value of γ is smaller than 4, the value predicted by de Gennes' theory for the case of molecules for which Z tends to infinity. The inelastic part of the spectrum has been analyzed in terms of the Krieger—Nelkin approximation with a single effective mass. The effective mass obtained in the case of both scattering samples is much less than the real mass of the chain perhaps showing that the neutrons are sensitive to the rotation of the (CH2) groups. The agreement between the theory and experiment is not satisfactory in the inelastic case, indicating the need for a more sophisticated theory than the one used in our analysis.