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Kinetics of aggregation in micellar solutions of thermoresponsive triblock copolymers - influence of concentration, start and target temperatures

  • In aqueous solution, symmetric triblock copolymers with a thermoresponsive middle block and hydrophobic end blocks form flower-like core-shell micelles which collapse and aggregate upon heating through the cloud point (CP). The collapse of the micellar shell and the intermicellar aggregation are followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while heating micellar solutions of a poly((styrene-d(8))-b-(N-isopropyl acrylamide)-b-(styrene-d(8))) triblock copolymer in D2O rapidly through their CP. The influence of polymer concentration as well as of the start and target temperatures is addressed. In all cases, the micellar collapse is very fast. The collapsed micelles immediately form small clusters which contain voids. They densify which slows down or even stops their growth. For low concentrations and target temperatures just above the CP, i.e. shallow temperature jumps, the subsequent growth of the clusters is described by diffusion-limited aggregation. In contrast, for higherIn aqueous solution, symmetric triblock copolymers with a thermoresponsive middle block and hydrophobic end blocks form flower-like core-shell micelles which collapse and aggregate upon heating through the cloud point (CP). The collapse of the micellar shell and the intermicellar aggregation are followed in situ and in real-time using time-resolved small-angle neutron scattering (SANS), while heating micellar solutions of a poly((styrene-d(8))-b-(N-isopropyl acrylamide)-b-(styrene-d(8))) triblock copolymer in D2O rapidly through their CP. The influence of polymer concentration as well as of the start and target temperatures is addressed. In all cases, the micellar collapse is very fast. The collapsed micelles immediately form small clusters which contain voids. They densify which slows down or even stops their growth. For low concentrations and target temperatures just above the CP, i.e. shallow temperature jumps, the subsequent growth of the clusters is described by diffusion-limited aggregation. In contrast, for higher concentrations and/or higher target temperatures, i.e. deep temperature jumps, intermicellar bridges dominate the growth. Eventually, in all cases, the clusters coagulate which results in macroscopic phase separation. For shallow temperature jumps, the cluster surfaces stay rough; whereas for deep temperature jumps, a concentration gradient develops at late stages. These results are important for the development of conditions for thermal switching in applications, e.g. for the use of thermoresponsive micellar systems for transport and delivery purposes.show moreshow less

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Metadaten
Author:Joseph Adelsberger, Isabelle Grillo, Amit Kulkarni, Melissa Sharp, Achille M. Bivigou-Koumba, André LaschewskyORCiDGND, Peter Müller-Buschbaum, Christine M. Papadakis
DOI:https://doi.org/10.1039/c2sm27152d
ISSN:1744-683X (print)
Parent Title (English):Soft matter
Publisher:Royal Society of Chemistry
Place of publication:Cambridge
Document Type:Article
Language:English
Year of first Publication:2013
Year of Completion:2013
Release Date:2017/03/26
Volume:9
Issue:5
Pagenumber:15
First Page:1685
Last Page:1699
Funder:DFG [Pa771/4, Mu1487/8, La611/7, SPP1259]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Chemie
Peer Review:Referiert