Effect of Temperature and Ionic Strength on Micellar Aggregates of Oppositely Charged Thermoresponsive Block Copolymer Polyelectrolytes

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  • Bence Fehér, Eötvös Loránd University
  • ,
  • Kaizheng Zhu, Universitetet i Oslo
  • ,
  • Bo Nyström, Universitetet i Oslo
  • ,
  • Imre Varga, Eötvös Loránd University
  • ,
  • Jan Skov Pedersen

The self-assembly of two oppositely charged diblock copolymers that have a common thermosensitive nonionic block of poly(N-isopropylacrylamide) (pNIPAAM) has been investigated. The effect of the mixing ratio and total polymer concentrations on the self-assembly of the components and on the phase stability of the mixtures was studied by dynamic light scattering, electrophoretic mobility, and turbidimetry measurements in water at 20 °C. The effect of the competing electrostatic and hydrophobic interactions on the nanostructure of negatively charged electrostatically self-assembled micelles bearing a pNIPAAM corona was investigated by small-angle X-ray scattering (SAXS). The electrostatic and hydrophobic interactions were controlled independently by tuning the ionic strength (from pure water to 50 mM NaCl) and the temperature (20-50 °C) of the investigated mixtures. The SAXS data could be fitted by a spherical micelle model, which has a smoothly decaying radial profile and a Gaussian star term that describes the internal structure of the micellar structures and possible attractive interactions between the polymer chains. At high temperature, a cluster structure factor was included for describing the formation of bulky clusters of the formed micelles. At low temperature and ionic strength, the formation of micelles with a coacervate core and hydrated pNIPAAM shell was observed. The structural evolution of the self-assembled micelles with increasing ionic strength and temperature could be followed, and finally at high ionic strength and temperature, the formation of inverted micelles with a hydrophobic core and polyelectrolyte shell could be identified.

OriginalsprogEngelsk
TidsskriftLangmuir
Vol/bind35
Nummer42
Sider (fra-til)13614-13623
Antal sider10
ISSN0743-7463
DOI
StatusUdgivet - 2019

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