Stimuli-induced core-corona inversion of micelles of water-soluble poly(sodium 2-(acrylamido)-2-methyl propanesulfonate-b-N-isopropylacrylamide)

Micelles of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate-b-N-isopropylacrylamide) (PAMPS-b-PNIPAM) have been investigated in aqueous solutions using various techniques including dynamic light scattering, scanning electron microscopy, transmission electron microscopy and ζ-potential measurements. It was found that PAMPS-b-PNIPAM produces two distinct types of micelle structures; one is a PAMPS-core/PNIPAM-corona structure and the other is a PNIPAM-core/PAMPS-corona structure. The PAMPS-core micelle with the PNIPAM-corona was obtained by insolubilizing the PAMPS block with ferric ion (Fe3+) at room temperature, and the PNIPAM-core micelle with the PAMPS-corona was obtained by increasing the solution temperature above the lower critical solution temperature (LCST) of the PNIPAM block in the absence of the Fe3+ ion. We have also found that the inversion from one type to the other is reversible. The transformation from the PAMPS-core micelle to the PNIPAM-core micelle was induced by removing Fe3+ ion using ethylenediaminetetraacetic acid followed by elevating the temperature above the LCST of the PNIPAM block, while the reverse transformation was triggered by adding Fe3+ ion at a lower temperature.