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The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N‐isopropylacrylamide) Star Polymers

Zhu, Kaizheng ; Pamies, Ramón ; Al‐Manasir, Nodar ; Ginés Hernández Cifre, José ; García de la Torre, José ; Nyström, Bo ; Kjøniksen, Anna‐Lena

Chemphyschem, 2020-06, Vol.21 (12), p.1258-1271 [Periódico revisado por pares]

Germany: Wiley Subscription Services, Inc

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  • Título:
    The Effect of Number of Arms on the Aggregation Behavior of Thermoresponsive Poly(N‐isopropylacrylamide) Star Polymers
  • Autor: Zhu, Kaizheng ; Pamies, Ramón ; Al‐Manasir, Nodar ; Ginés Hernández Cifre, José ; García de la Torre, José ; Nyström, Bo ; Kjøniksen, Anna‐Lena
  • Assuntos: Agglomeration ; Aggregates ; Aqueous solutions ; Computer simulation ; dynamic light scattering ; Low temperature ; Monte Carlo simulations ; Photon correlation spectroscopy ; poly(N-isopropylacrylamide) ; Polyisopropyl acrylamide ; Polymers ; Rheological properties ; Rheology ; Size reduction ; star polymers ; Temperature ; thermoresponsive ; Turbidity
  • É parte de: Chemphyschem, 2020-06, Vol.21 (12), p.1258-1271
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
  • Descrição: The thermoresponsive nature of aqueous solutions of poly(N‐isopropylacrylamide) (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. How many arms? Aqueous solutions of poly(N‐isopropylacrylamide) (PNIPAAM) star polymers exhibit a complex thermosensitive behavior. Increasing the number of arms promotes aggregation below the cloud point. When the temperature is raised, there is a competition between size increase due to enhanced aggregation and a size reduction caused by contraction. Some of the samples exhibits fragmentation of the aggregates at temperatures above the cloud point, followed by re‐aggregation at even higher temperatures.
  • Editor: Germany: Wiley Subscription Services, Inc
  • Idioma: Inglês;Norueguês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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