Direct measurement of the penetration of free chains into a tethered chain layer

Direct measurements of the penetration of free chains into a layer of tethered chains in good solvent conditions are reported. The segmental profiles of both the tethered chains (N = 1625 monomer units) and the free chains (P = 413 and 3846 monomer units) are obtained by neutron reflection. At 6 vol. %, the free chains penetrate the tethered layer at low surface density (sigma), but are progressively excluded from the layer with increasing sigma. At the highest sigma (sigma pi R-g(2) congruent to 12) there remains significant penetration into the layer for both values of P; however, the form of the profile is strikingly different.