Effect of cosolvent on the rheological properties and self-assembled structures from telechelic polyampholytes
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INVITED ARTICLE
Effect of cosolvent on the rheological properties and self-assembled structures from telechelic polyampholytes Margarita A. Dyakonova 1 & Yanan Li 1 & Ioanna N. Besiri 2 & Zhenyu Di 3 & Isabelle Grillo 4 & Constantinos Tsitsilianis 2 & Christine M. Papadakis 1 Received: 30 July 2020 / Revised: 19 September 2020 / Accepted: 25 September 2020 # The Author(s) 2020
Abstract A triblock copolymer with hydrophobic end blocks and a polyampholytic middle block is investigated in a mixture of water and acetone with a focus on the dependence of the rheological properties and of the micellar structure and correlation on the content of acetone. The polymer under study is PMMA86-b-P(DEA190-co-MAA96)-b-PMMA86, where PMMA stands for poly(methyl methacrylate) and P(DEA-co-MAA) for poly(2-(diethylamino) ethyl methacrylate-co-methacrylic acid). The pH is chosen at 3. Rheological measurements reveal a transition from a viscoelastic solid over a viscoelastic liquid to a freely flowing liquid upon addition of 5 or 10 wt% of acetone to a 3 wt% aqueous polymer solution, respectively. Using small-angle neutron scattering on 0.5 wt% polymer solutions in water/acetone with the content of the latter ranging between 0 and 30 wt%, significant structural changes are observed as well, such as a decrease of the distance between the PMMA cross-links and of the size of the network clusters upon increasing acetone constant. These changes are attributed to the reduction of the dielectric constant by the addition of the cosolvent acetone, enhancing the flexibility of the middle blocks and their tendency to backfolding, as well as to the decrease of the solvent selectivity, inducing significant exchange rate enhancement of the core-forming PMMA blocks. Keywords Triblock copolymers . Cosolvent . Rheology . Small-angle neutron scattering
Introduction Self-assembled hydrogels from telechelic polymers form by hydrophobic interaction, i.e., the hydrophobic end blocks form micelles and a part of the hydrophilic blocks form elastic bridges [1–4]. Using polyelectrolytes as the middle blocks, hydrogels which are responsive to pH and ionic strength have been designed [5–11]. Using a polyampholyte middle block This paper is dedicated to the late Isabelle Grillo. * Christine M. Papadakis [email protected] 1
Physik-Department, Fachgebiet Physik weicher Materie, Technische Universität München, James-Franck-Str. 1, 85748 Garching, Germany
2
Department of Chemical Engineering, University of Patras, 26504 Patras, Greece
3
Jülich Centre for Neutron Science at MLZ, Forschungszentrum Jülich GmbH, Lichtenbergstr. 1, 85748 Garching, Germany
4
Large Scale Structures Group, Institut Laue-Langevin, 71, Avenue des Martyrs, 38042 Grenoble, France
has the advantage of an even stronger pH response. However, non-equilibrium states cannot be excluded especially for long and strongly hydrophobic blocks [4]. We investigated previously a telechelic polyampholyte, namely PMMA-b-P(DEA-co-MAA)-b-PMMA, where PMMA stands for poly(methyl methacrylate) and P(DEAco-MAA
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