Block Copolymer Adsorption at the Polymer Melt/Substrate Interface: The Effect of Matrix Competition

Abstract

Using low-energy forward recoil spectrometry (LE-FRES) and neutron reflectivity (NR), the interfacial excess, z *, of an asymmetric poly(deuterated styrene- 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) (PBr x S) matrix systematically increased. For matrix degrees of polymerization, P = 480 and 3846, z * decreased by 15% and 33%, respectively, as x increased. Neglecting the matrix−substrate interaction energy,, self-consistent mean-field (SCMF) calculations predicted an increase in z * with x, consistent with an increase in unfavorable matrix−dPS interactions, χ. By including a small attractive interaction ( = −0.01 k B T ) between the matrix and substrate, the SCMF z * decreased by ca. 50%, in qualitative agreement with experiments. Thus, as x increased (and therefore ), matrix chain competition for silicon oxide counteracts the expected increased adsorption due to χ. Furthermore, the dPS volume fraction profile in PBr 0.136 S had a lower z * and was thinner than for the neutral matrix case.