Adsorbed polymers: Neutron reflectivity and concentration profiles

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Abstract
We have determined by neutronreflectivity the volume fraction profile, φ(z) of poly(dimethylsiloxane) chains in toluene adsorbed at the free surface of the solution. φ(z) is found to vary as (a/z)4/3 conforming to scaling laws proposed by de Gennes. The extension of the profile is of the order of the radius of gyration. To arrive at these results, the use of two different isotopic compositions and the simultaneous analysis of results obtained with various polymer chain lengths and concentrations are necessary. The validity of several models has been tested. With a few realistic hypotheses compatible with already existing experimental data, it appears that only the self‐similar profile is acceptable for the system studied.