Asymmetric swelling and self-assembly of poly(N-isopropyl-acrylamide)-block-poly(ethylene glycol) in water

This investigation focused on the self-assembly of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) (PNIPA-b-PEG) in water. We distinguish four regions in the phase diagram: a transparent sol, opaque sol, opaque gel, and syneresis. Small-angle neutron scattering measurements revealed that microphase separation occurs above 17 ∘ C to form disordered micelles, which includes a range of states from (i) asymmetric swelling to (ii) micelle formation with only short-range liquid-like order. This result may be attributed to the action of water, which starts to behave as a selective solvent for PEG blocks; the PEG chains are more swollen with water than are the PNIPA chains.