Two distinct types of micelle structures have been successfully obtained from poly(ethylene oxide-b-methacrylic acid) (PEO-b-PMAA) in aqueous solutions: one with a PEO-core surrounded by a PMAA corona and the other with a PMAA-core surrounded by a PEO-corona. The PLO-core micelles were obtained by decreasing the cloud point of the PEO to room temperature by adding phosphate ions (PO43-), and the PMAA-core micelles were obtained by reducing the solubility of the PMAA block by adding calcium ions (Ca2+). The reversibility between the PMAA-core and PEO-core micelles was also confirmed; (1) the transformation from the PMAA-core to PEO-core micelles was achieved by solubilizing the PMAA block by removing Ca2+ with ethylenediaminetetraacetic acid followed by the addition of PO43-, and (2) the reverse transformation was carried out by removing PO43- by dialysis followed by the addition of Ca2+. The two types of micelles were characterized using various techniques such as turbidimetry, dynamic light scattering, scanning electron microscopy and electrophoretic light scattering. (C) 2010 Elsevier Inc. All rights reserved.