|365. Walther, A.; Barner-Kowollik, C.; Müller, A.H.E.: Mixed, Multicompartment, or Janus Micelles? A Systematic Study of Thermoresponsive Bis-Hydrophilic Block Terpolymers, Langmuir 26(14), 12237 (2010) -- DOI: 10.1021/la101173b|
We present a systematic investigation of the extent of compartmentalization in micelles formed by a series of bis-hydrophilic block terpolymers with two outer water-soluble segments. The corona blocks are constructed from poly(ethylene oxide) (PEO) and the thermo-responsive 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 thermo-responsive 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 a last section, we relate our results to previously studied systems and attempt to derive some generalities. Firstly, we try to answer the question how likely it is in terms of thermodynamics to obtain truly self-assembled 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-to-hydrophobic phase transition is triggered in one of the blocks.
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- Project: DFG-ARC (447 AUS-113/24/0-1): Living Free Radical Polymerizations for Nanotechnology Applications