Mixed, multicompartment, or janus micelles? A systematic study of thermoresponsive bis-hydrophilic block terpolymers

Andreas Walther*, Christopher Barner-Kowollik, Axel H E Müller

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

70 Citations (Scopus)

Abstract

We present a systematic investigation of the extent of compartmentalization in micelles formed by a series of bishydrophilic block terpolymers with two outer water-soluble segments. The corona blocks are constructed from poly(ethylene oxide) (PEO) and the thermoresponsive poly(N-isopropyl-acrylamide) (PNiPAAm). The fraction of PNiPAAm is varied to establish its influence on the supramicellar aggregation and corona phase behavior. We demonstrate that-when the collapse of PNiPAAm is triggered-a clustering of micelles into superstructures only occurs when the contour length of the thermoresponsive block is longer than that of the PEO chains. The volume fractions play a minor role. The extent of superstructure formation increases with the amount of heating cycles, pointing to a rearrangement of micelles with a mixed corona into a phase-segregated corona. The collapse of PNiPAAm is exploited to artificially raise the incompatibility and drive phase segregation. A uniform population of biphasic Janus micelles cannot be obtained. After repeated heating cycles, the mixture consists of a range of multicompartment architectures, whose patch distribution can be derived from aggregate structures found in cryo-TEM obtained at high temperature. In the last section, we relate our results to previously studied systems and attempt to derive some generalities. First, we try to answer the question of how likely it is in terms of thermodynamics to obtain truly selfassembled Janus micelles. Furthermore, our results can provide an estimation for the volume ratio or/and block lengths required in micelles composed out of two corona blocks to induce supramicellar aggregation when a hydrophilic-tohydrophobic phase transition is triggered in one of the blocks.

Original languageEnglish
Pages (from-to)12237-12246
Number of pages10
JournalLangmuir
Volume26
Issue number14
DOIs
Publication statusPublished - 20 Jul 2010
MoE publication typeA1 Journal article-refereed

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