title: Imaging the volume transition in thermosensitive core-shell particles by cryo-transmission electron microscopy.
abstract: We report a study of colloidal thermosensitive core-shell particles by cryo-transmission electron microscopy (cryo-TEM). The particles consist of a solid core of poly(styrene), onto which a network of cross-linked poly(N-isopropylacrylamide) (PNIPAM) is affixed. In water, the shell of these particles swells when the temperature is low. Raising the temperature above 32 degrees C leads to a marked shrinking of the shell. In this letter, we present the first study of these core-shell particles by cryo-TEM in situ, that is, in aqueous solution. We demonstrate that the core-shell particles are well-defined and exhibit a narrow size distribution. In particular, the PNIPAM shell is compact and has a defined outer surface of a slightly irregular shape. The micrographs show that there are density fluctuations within the network. Cryo-TEM of the system above and below the transition temperature furnishes information about the thermosensitive particles that had not been available through other methods employed in previous investigations.
authors.affiliation: Physikalische Chemie I, University of Bayreuth, 95440 Bayreuth, Germany.
authors.forename: Jérôme J
authors.initials: JJ
authors.lastname: Crassous
authors.forename: Matthias
authors.initials: M
authors.lastname: Ballauff
authors.forename: Markus
authors.initials: M
authors.lastname: Drechsler
authors.forename: Judith
authors.initials: J
authors.lastname: Schmidt
authors.forename: Yeshayahu
authors.initials: Y
authors.lastname: Talmon