© Copyright 2007 American Chemical Society
APRIL 24, 2007 VOLUME 23, NUMBER 9
Letters Controlled Stacking of Charged Block Copolymer Micelles Zhibin Li,†,§ Zhiyun Chen,‡ Honggang Cui,† Kelly Hales,† Karen L. Wooley,*,‡ and Darrin J. Pochan*,† Materials Science and Engineering and Delaware Biotechnology Institute, UniVersity of Delaware, Newark, Delaware 19716, and Center for Materials InnoVation and Department of Chemistry, Washington UniVersity in Saint Louis, Saint Louis, Missouri 63130 ReceiVed NoVember 10, 2006. In Final Form: January 19, 2007 Using poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) triblock copolymers or a mixture of different molecular weight PAA-b-PS diblock copolymers, stacks of polymeric micellar assemblies, such as disks and Y-shaped cylinders, were formed through intermicellar interactions. Whereas micelles hierarchically stacked together, micellar interactions within the stack defined a uniform micelle geometry and size for up to micrometers in length. The kinetic pathway dependence and stability of the stacked assemblies were studied, and possible intermicellar interactions between micelles within the stacks are proposed.
Nanoscale phase separation of block copolymers in bulk and thin film systems has been used to form bulk functional materials and patterned surfaces.1-6 Amphiphilic block copolymers that assemble into polymer micelles have also been studied for nanotechnology applications7-12 and drug-delivery systems.13-18 In this letter, stacks of polymer micellar assemblies, such as * Corresponding authors. E-mail:
[email protected], klwooley@ artsci.wustl.edu. † University of Delaware. ‡ Washington University in Saint Louis. § Present address: Boehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, Connecticut 06877. (1) Whitesides, G. M. Small 2005, 1, 172-179. (2) Russell, T. P. Curr. Opin. Colloid Interface Sci. 1996, 1, 107-115. (3) Granick, S.; Kumar, S. K.; Amis, E. J.; Antonietti, M.; Balazs, A. C.; Chakraborty, A. K.; Grest, G. S.; Hawker, C.; Janmey, P.; Kramer, E. J.; Nuzzo, R.; Russell, T. P.; Safinya, C. R. J. Polym. Sci., Part B: Polym. Phys. 2003, 41, 2755-2793. (4) Fasolka, M. J.; Mayes, A. M. Annu. ReV. Mater. Res. 2001, 31, 323-355. (5) Bates, F. S. Science 1991, 251, 898-905. (6) Yan, X.; Liu, G.; Li, Z. J. Am. Chem. Soc. 2004, 126, 10059-10066. (7) Vriezema, D. M.; Aragones, M. C.; Elemans, J. A. A. W.; Cornelissen, J. J. L. M.; Rowan, A. E.; Nolte, R. J. M. Chem. ReV. 2005, 105, 1445-1489. (8) Behera, D. K.; Bag, D. S.; Alam, S.; Mathur, G. N. J. Polym. Mater. 2004, 21, 81-88. (9) Wooley, K. L. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 13971407. (10) Foerster, S.; Antonietti, M. AdV. Mater. 1998, 10, 195-217.
disks, cylinders, and Y-shaped cylinders (Ys), are reported, which form from amphiphilic linear block copolymers in tetrahydrofuran (THF)/water solvent mixtures. These well-arranged, stacked micelle structures form in solution compositions that exist between those that produce regions of bulk phase separation versus those that produce a discrete micellization of block copolymers. Figure 1 shows micro- and nanoscale image examples of bulk phase separation, stacked micelles, and separated/discrete micelles. The block copolymer bulk phase separation forms a lamellar precipitate, stacks of disks exist in an optically cloudy solution without precipitation, and the solution of discrete micelles is (11) Moffitt, M.; Zhang, L.; Khougaz, K.; Eisenberg, G. A. NATO ASI Ser., Ser. E 1996, 327, 53-72. (12) Zhang, L.; Eisenberg, A. Science 1995, 268, 1728-1731. (13) Gaucher, G.; Dufresne, M.-H.; Sant, V. P.; Kang, N.; Maysinger, D.; Leroux, J.-C. J. Controlled Release 2005, 109, 169-188. (14) Le Garrec, D.; Ranger, M.; Leroux, J.-C. Am. J. Drug DeliVery 2004, 2, 15-42. (15) Nishiyama, N.; Bae, Y.; Miyata, K.; Fukushima, S.; Kataoka, K. Drug DiscoVery Today: Technol. 2005, 2, 21-26. (16) Vasir, J. K.; Reddy, M. K.; Labhasetwar, V. D. Curr. Nanosci. 2005, 1, 47-64. (17) Otsuka, H.; Nagasaki, Y.; Kataoka, K. AdV. Drug DeliVery ReV. 2003, 55, 403-419. (18) Adams Monica, L.; Lavasanifar, A.; Kwon Glen, S. J. Pharm. Sci. 2003, 92, 1343-1355.
10.1021/la063292b CCC: $37.00 © 2007 American Chemical Society Published on Web 03/31/2007
4690 Langmuir, Vol. 23, No. 9, 2007
Letters
Figure 1. Phase behavior for S203 triblock copolymers in THF/water solvent mixtures with the addition of EDDA diamine in a 1:1 amine/acid ratio. (Top) At low water content (
