Core-shell morphology in poly(N-isopropyl acrylamide) copolymer gels induced by restricted diffusion of surfactant

In this paper, we report on the synthesis of copolymer gels of poly(N-isopr opyl acrylamide) and poly(acryloyl aminoacids) and their interaction with a nionic surfactant, namely, sodium dodecyl sulfate (SDS). While we were stud ying the swelling behavior of these copolymer gels in SDS solutions, we obs erved core-shell morphology in the swollen gels along with two discontinuou s volume transitions. Such morphologies have potential applications in drug delivery systems. We provide a mechanistic interpretation of these new obs ervations on the basis of electrostatic charge repulsion and restricted dif fusion of surfactant into the gel.