Segmental motion of alkyl chains grafted on silica gel, studied by neutron scattering

J.P. Beaufils , M. C. Hennion , R. Rosset

The quasielastic neutron scattering spectra of CnH2n+ 1 grafted on silica are obtained for n = 4, 8,12, 16,18, 22. The well known difficulty in determining the mass in the beam is overcome by using (as a reference) the integrated elastic and quasielastic scattering function, extrapolated to q = 0. A correction for the coherent scattering contribution is applied. It is thus possible to determine the molar scattering functions of the chains Sn(q, ω). Assuming that in all chains there is a constant number ne of end atoms contributing Se to Sn for all n and that the remaining middle CH2 are all equivalent, each contributing S m to Sn, we obtain Sn = Se + (n - n e) Sm. This relationship is verified for the elastic incoherent structure factor and used to calculate Sm. The n = 22 case is left apart, its anomalous behaviour is explained by interaction between neighbouring chains. The data agree with a 3-bonds jump model with a time between jumps equal to 1.9 x 10-11 s at room temperature.

Mots clés: gels; neutron diffraction examination of materials; organic compounds; silicon compounds

Domaines: Articles anciens

J.P. Beaufils, M. C. Hennion, R. Rosset. Segmental motion of alkyl chains grafted on silica gel, studied by neutron scattering. Journal de Physique, 1983, 44 (4), pp.497-503. ⟨10.1051/jphys:01983004404049700⟩. ⟨jpa-00209623⟩