Imaging the Volume Transition in Thermosensitive Core−Shell Particles by Cryo-Transmission Electron Microscopy

• Published in: Langmuir Vol. 22; no. 6; pp. 2403 - 2406
• Main Authors: Crassous, Jérôme J, Ballauff, Matthias, Drechsler, Markus, Schmidt, Judith, Talmon, Yeshayahu
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14-03-2006
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry; Water; Fluctuations; Transition temperature; Shape; Hydrocarbon; In situ; Density; Solid; Particle; Transmission electron microscopy; Imaging; Distribution; Styrene; Benzenic compound; Aqueous solution; Low temperature
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la053198f

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 °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.