Publication: The effect of number of arms on the aggregation behavior of thermoresponsive poly (N-isopropylacrylamide) star polymers
Authors
Zhu, Kaizheng ; Pamies, Ramón ; Al-Manasir, Nodar ; Hernández Cifre, José G. ; García de la Torre, José ; Nyström, Bo ; Kjøniksen, Anna-Lena
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Publisher
Wiley
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DOI
https://doi.org/10.1002/cphc.202000273
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info:eu-repo/semantics/article
Description
© 2020 The Authors. This manuscript version is made available under the CC-BY 4.0 license http://creativecommons.org/licenses/by/4.0/
This document is the Published Manuscript version of a Published Work that appeared in final form in ChemPhysChem. To access the final edited and published work see https://doi.org/10.1002/cphc.202000273
Abstract
The thermoresponsive nature of aqueous solutions of poly(Nisopropylacrylamide) (PNIPAAM) star polymers containing 2, 3, 4, and 6 arms has been investigated by turbidity, dynamic light scattering, rheology, and rheo-SALS. Simulations of the thermosensitive nature of the single star polymers have also been conducted. Some of the samples form aggregates even at temperatures significantly below the lower critical solution temperature (LCST) of PNIPAAM. Increasing concentration and number of arms promotes associations at low temperatures.
When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Monte Carlo simulations show that the single stars contract with increasing temperature, and that this contraction is more pronounced when the number of arms is increased. Some samples exhibit a minimum in the turbidity data after the initial increase at the cloud point. The combined rheology and rheo-SALS data suggest that this is due to a fragmentation of the aggregates followed by re-aggregation at even higher temperatures. Although the 6-arm star polymer aggregates more than the other stars at low temperatures, the more compact structure renders it less prone to aggregation at temperatures above the cloud point.
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Citation
ChemPhysChem, 2020, Vol. 21, Issue12, pp. 1258-1271
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Este ítem está sujeto a una licencia Creative Commons. http://creativecommons.org/licenses/by/4.0/