Nanocavities via amphiphilic block copolymer thin films

PMSE 124

Andrew C. Miller, acmiller@mit.edu1, Ryan D. Bennett1, Paula T. Hammond, hammond@mit.edu1, Robert E. Cohen1, and Darrell J. Irvine2. (1) Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, (2) Department of Materials Science and Engineering/Department of Biological Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Room 8-425, Cambridge, MA 02139
We investigated the structure of thin films formed from close-packed poly(styrene-b-polyacrylic acid) (PS-b-PAA) inverse micelles cast on solid substrates following exposure to aqueous solutions or alcohols of varying polarity. These micelles formed close-packed spheres when cast on solid substrates from toluene solutions, but on exposure to polar solvents, the micelles ‘cavitated': the PAA cores swelled, fracturing the glassy polystyrene corona. The cavitation behavior of three different PS-b-PAA molecular weights was characterized using AFM and TEM following exposure of films to aqueous solutions of varying pH and ionic strength, or a series of alcohols of increasing alkyl chain length. In addition, we demonstrated the availability of PAA groups at the film surface by derivatizing cavitated films with fluorescent markers. Cavitation of micelle films was found to depend on the pH and ionic strength of the aqueous medium, as well as the molecular weight of the PS corona of the micelles.