Contrast variation small-angle neutron scattering study of the structure of block copolymer micelles in a slightly selective solvent at semidilute concentrations

Jan Skov Pedersen, Ian W. Hamley, Chang Yeol Ryu, Timothy P. Lodge

Research output: Contribution to journalArticle

65 Scopus citations

Abstract

The structure of micelles of an asymmetric polystyrene-polyisoprene (PS-PI) diblock copolymer has been studied in di-n-butyl phthalate (DBP), which is a slightly selective solvent for PS. The polymer has a molecular weight of 11 500 for the fully deuterated d-PS block and 48 500 for the PI block. Contrast variation SANS using mixtures of protonated and deuterated solvent and a polymer volume fraction of 18% at 10 °C were performed to get detailed information on the structure of the micelles. An additional contrast was obtained by performing a small-angle X-ray scattering measurement on a sample in protonated DBP. It was found that micelles are formed with an anisometric PI-rich core surrounded by dissolved d-PS chains. The data were analyzed using model form factors of micelles with, respectively, cylindrical and ellipsoidal cores. It was necessary to include a term to describe the concentration fluctuations within the swollen PI cores. The particle interference effects originating from the high volume fraction were described by a hard-sphere structure factor. Both models fit the data well, however, a cylindrical model which includes size polydispersity gives the best fit.

Original languageEnglish (US)
Pages (from-to)542-550
Number of pages9
JournalMacromolecules
Volume33
Issue number2
DOIs
StatePublished - 2000

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