Diblock copolymers attached to homopolymer surfaces and interfaces

Abstract

Nuclear reaction analysis (NRA) was used to study the segregation of an asymmetric diblock copolymer, consisting of polyisoprene (PI, molecular weight M = lV)/deuterated polystyrene (dPS, M = 105) blocks, to the interfaces formed by polystyrene (PS) homopolymer with various phases. PS/vacuum, PSI silicon, and PS/PI homopolymer interfaces were investigated for different M values of the PS matrix (M = 1.7 X lo3-330 X lo3), and segregation isotherms were established as a function of temperature and of diblock concentration within the PS homopolymer. In all cases the diblocks attach to the interfaces by their PI moieties alone, to form brushlike structures of end-attached PS tails. The high spatial resolution of the NRA technique enabled studies of the brush conformation as a function of the attachment density at the PS/ vacuum surface and was used to characterize the extent of penetration of the PS matrix chains into the diblock brushes. Detailed analysis of the brush conformation and of the segregation isotherms, mainly in terms of a Flory-type mean field model based on those due to de Gennes and to Leibler, provided a consistent description of our data, it enabled the extraction of the PI/PS segmental interaction parameter XPIPS, yielding values in accord with scattering studies, and of the attachment energies of the PI diblock moiety to the PS/air and PS/silicon interfaces. The values of xpps extracted from our data using this Flory-type model were found to increase at lower M values of the PS matrix, in qualitative accord with previous results.