Unraveling an Alternative Mechanism in Polymer Self-Assemblies: An Order-Order Transition with Unusual Molecular Interactions between Hydrophilic and Hydrophobic Polymer Blocks

Lukas Hahn, Theresa Zorn, Josef Kehrein, Tobias Kielholz, Anna Lena Ziegler, Stefan Forster, Benedikt Sochor, Ekaterina S. Lisitsyna, Nikita A. Durandin, Timo Laaksonen, Vladimir Aseyev, Christoph Sotriffer, Kay Saalwächter, Maike Windbergs, Ann Christin Pöppler, Robert Luxenhofer

Research output: Contribution to journalArticleScientificpeer-review

7 Citations (Scopus)
20 Downloads (Pure)

Abstract

Polymer self-assembly leading to cooling-induced hydrogel formation is relatively rare for synthetic polymers and typically relies on H-bonding between repeat units. Here, we describe a non-H-bonding mechanism for a cooling-induced reversible order-order (sphere-to-worm) transition and related thermogelation of solutions of polymer self-assemblies. A multitude of complementary analytical tools allowed us to reveal that a significant fraction of the hydrophobic and hydrophilic repeat units of the underlying block copolymer is in close proximity in the gel state. This unusual interaction between hydrophilic and hydrophobic blocks reduces the mobility of the hydrophilic block significantly by condensing the hydrophilic block onto the hydrophobic micelle core, thereby affecting the micelle packing parameter. This triggers the order-order transition from well-defined spherical micelles to long worm-like micelles, which ultimately results in the inverse thermogelation. Molecular dynamics modeling indicates that this unexpected condensation of the hydrophilic corona onto the hydrophobic core is due to particular interactions between amide groups in the hydrophilic repeat units and phenyl rings in the hydrophobic ones. Consequently, changes in the structure of the hydrophilic blocks affecting the strength of the interaction could be used to control macromolecular self-assembly, thus allowing for the tuning of gel characteristics such as strength, persistence, and gelation kinetics. We believe that this mechanism might be a relevant interaction pattern for other polymeric materials as well as their interaction in and with biological environments. For example, controlling the gel characteristics could be considered important for applications in drug delivery or biofabrication.

Original languageEnglish
Pages (from-to)6932–6942
Number of pages11
JournalACS Nano
Volume17
Issue number7
DOIs
Publication statusPublished - 2023
Publication typeA1 Journal article-refereed

Keywords

  • inverse thermogelation
  • molecular dynamics simulation
  • NMR spectroscopy
  • poly(2-oxazine)
  • poly(2-oxazoline)

Publication forum classification

  • Publication forum level 3

ASJC Scopus subject areas

  • General Materials Science
  • General Engineering
  • General Physics and Astronomy

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