Sprecher
Beschreibung
Concentrated solutions and gels of block copolymer micelles demonstrate both the cohesive strength of solids and the diffusive transport characteristics of liquids, and are subject of theoretical and technological interest [1]. Special attention is devoted to polymers containing a stimuli-responsive "switching" block that imparts the system the ability to undergo sharp, reversible changes in response to variation of external control parameters (e.g. temperature)[2]. In this work we investigate the behaviour of diblock and triblock copolymers containing thermoresponsive poly-N-isopropyl acrylamide (PNIPAM) and persistently hydrophobic polystyrene (PS) blocks, in concentrated water solution [3]. The polymers form spherical micelles in water, whose strucural parameteres have been determined by small-angle neutron scattering (SANS). At high concentration, the micellar samples show a completely different rheological behaviour depending on block size and, most importantly, architecture. In particular, a “soft” gel is formed in triblock-containing samples as the triblocks form junctions bridging different micellar cores. At the microscopic level, the PNIPAM chain mobility is influenced by the size and architecture of the polymer as well as topological constrains induced by the grafting on the PS core. Neutron spin echo (NSE) data shows how the single-chain dynamics is at best described by Zimm with one end fixed and additional internal friction between monomers. A characteristic modulation in the dynamics related to the geometrical arrangement is found. Side chains are mobile but strongly constrained by a much slower backbone. The theoretical approach derived herein can serve as a framework for describing other systems in which polymeric junctions play a significant role [4].
[1] R. Ganguly et al., J. J. Mol. Liq. 2020, 314, 113591. R. Tamate et al., Adv. Mat. 2018, 30, 1802792.
[2] A. Nykänen et al., Macromolecules 2007, 40(16), 5827–5834. S. P. Sridhar et al., Surfaces and Interfaces 2020, 21, 100800. S. Kirkland et al., Biomacromolecules 2008, 9, 481–486.
[3] J. Adelsberger et al., Colloid Polym Sci 2011, 289, 711–720. J. Adelsberger et al., Macromolecules 2010, 43, 2490–2501.
[4] B. Rosi et al., Macromolecules 2025, 12, 13009-13021.