Characterization of the brush regime for grafted polymer layers at the solid-liquid interface by P. Auroy and others (1991, 10.1103/PhysRevLett.66.719)

Physical Review Letters 66, 719–722. The abstract identifies end-grafted polydimethylsiloxane on porous silicon dioxide and reports thickness proportional to $M\sigma$ in a poor solvent and $M{\sigma }^{1/3}$ in a good solvent. The chemical system in that abstract differs from the polystyrene wording of the 2016 exam; the scaling comparison is unaffected.