Self-assembly of block copolymer-based ionic supramolecules based upon multi-tail amphiphiles
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Utilising simple acid-base titration chemistry, a new family of Linear-b-Amphiphilic Comb (L-b-AC) ionic supramolecules [Soft Matter 2013, 9, 1540-1555] featuring multi-tail side-chains have been synthesized and examined by synchrotron SAXS. To three different parent diblock copolymers of poly(styrene)-b-poly( methacrylic acid) PS-b-PMAA multi-tail ammonium side-chains of (C8)(2)-, (C8)(4) -or (C12)(2)-type were attached at various side-chain grafting densities (X), making it possible to separate effects of the details of the AC-block architecture from effects of the overall volume fraction of the AC block. The micro-segregated morphologies of these systems include AC-block filled spherical microdomains in a liquid-like state (SPHLL), AC-block filled hexagonally-packed cylinders (CYL), alternating lamellar microlayers of AC- and L-blocks (LAM) and L-block filled hexagonally-packed cylinders (CYL*). For systems with the same parent diblock copolymer that also carry a constant volume fraction of AC-blocks, an increase in the side-chain length (l(sc)) and/or in the number of alkyl tails at a side-chain branch point (m) result in a microdomain morphology that is either unchanged or changed into one with a less curved interface. For lamellae-forming L-b-AC ionic supramolecules made up of the same parent diblock copolymer, a body of experimental data showing small variations in the repeat distance of the LAM micro-segregated structure (d(LAM)) could be obtained by making appropriate combinations of X, lsc and m. For such lamellae-forming L-b-AC ionic supramolecules, the average of d(LAM) values decreases when l(sc) and/or m increase. For systems with (C12)(2)-type side-chains, the effective Flory-Huggins interaction parameter between L-and AC-blocks chi'(C12)(2)/X was determined at various side-chain grafting densities and it was observed that chi'(C12)(2)/X increases when X is increased.