SEGREGATION STUDY OF A BAB TRIBLOCK COPOLYMER AT THE A B HOMOPOLYMER INTERFACE/

The segregation of a 2-vinylpyridine)-b-styrene-d8-b-(2-vinylpyridine) ] triblock copolymer (PVP-dPS-PVP) to a planar interface between the h omopolymers PS and PVP is determined by forward recoil spectrometry (F RES). Compared to a diblock copolymer of dPS-PVP with the same mole fr action of PVP (approximately 0.15) and total degree of polymerization (approximately 500), we find that the triblock copolymer interfacial e xcess z(i) at saturation is roughly half that of the diblock copolyme r. Self-consistent mean field theory produces a segregation isotherm i n fair agreement with the experimental results for the triblock copoly mer using the same value of the Flory parameter chi deduced for the di block copolymer. Both triblock and diblock copolymers show an increase in z(i) beyond the saturation plateau which is due to the condensati on of block copolymer micelles adjacent to the interface in the PS pha se. This increase for the triblock copolymer occurs at a copolymer vol ume fraction phi(infinity) = 0.15 in the PS phase, whereas for the dib lock copolymer it occurs at a much lower volume fraction, 0.05. This r esult indicates that the triblock copolymer has a larger critical mice lle concentration (CMC) than the diblock copolymer. While the condensa tion of diblock copolymer micelles at the surface occurs above the CMC , no such preferential segregation is observed for the triblock copoly mer. Transmission electron microscopy was used to examine the structur e of the triblock copolymer micelles at and near the interface.