Black copolymer adsorption at the polymer melt/substrate interface: The effect of matrix competition

Using low-energy forward recoil spectrometry (LE-FRES) and neutron reflecti vity (NR), the interfacial excess, z*, of an asymmetric poly(deuterated sty rene-block-methyl methacrylate) (dPS-b-PMMA) at the polymer matrix/silicon oxide interface was found to decrease as the bromostyrene mole fraction, x, in a poly(styrene-ran-4-bromostyrene) (PBrxS) matrix systematically increa sed. For matrix degrees of polymerization, P = 480 and 3846, z* decreased b y 15% and 33%, respectively, as x increased. Neglecting the matrix-substrat e interaction energy, epsilon(M)(s), self-consistent mean-field (SCMF) calc ulations predicted an increase in z* with x, consistent with an increase in unfavorable matrix-dPS interactions, gamma. By including a small attractiv e interaction (epsilon(M)(s) = -0.01 k(B)T) between the matrix and substrat e, the SCMF z* decreased by ca. 50%, in qualitative agreement with experime nt. Thus, as x increased (and therefore epsilon(M)(s)), matrix chain compet ition for silicon oxide counteracts the expected increased adsorption due t o chi. Furthermore, the dPS volume fraction profile in PBr0.136S had a lowe r z* and was thinner than for the neutral matrix case.