Synthesis and Surface Chemistry Study of a New Amphiphilic PAMAM Dendrimer Guodong Sui, Miodrag Micic, Qun Huo, and Roger M. Leblanc* Center for Supramolecular Science and Center for Advanced Microscopy, Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, Florida 33124 Received April 18, 2000. In Final Form: July 18, 2000 A new disk-shaped amphiphilic dendrimer has been synthesized by attaching sixty-four 12-hydroxy- dodecanoic acid chains to a fourth generation poly(amido amine) (PAMAM) dendrimer core. Surface pressure and surface potential-area isotherm measurements have shown that the dendrimer forms a stable monolayer at the air/water interface with limiting molecular area of 160 Å 2 /molecule. This small area relative to the huge size of the dendrimer suggests that the dendrimer molecules form an edge-on disk-shaped structure at the air/water interface. The topography of the dendrimer monolayer was observed by Brewster angle microscopy (BAM) at air/water interface as well as by environmental scanning electron microscopy (ESEM) as a Langmuir-Blodgett film. The striplike monolayer domains observed from BAM images correspond to the monolayer topography as observed from ESEM images. Introduction Langmuir and Langmuir-Blodgett films with novel molecular architectures have always been a focal point in surface chemistry research area. In the late 1980s and early 1990s, disklike molecules 1,2 have triggered the interest of surface chemists due to their unique anisotropic physical properties. Ringsdorf and Wendoff as well as other groups have investigated systematically the molecular structures and properties of various discotic molecules in Langmuir or Langmuir-Blodgett films and in bulk state. 3-8 Face-on and edge-on models were used to characterize the arrangement of the discotic molecules at the air-water interface (Figure 1). 3-5 The edge-on con- figuration was of more interest compared to the face-on configured monolayer, since the edge-on configured mono- layers are columnar Langmuir films which may display anisotropic transport properties related to electron trans- port, energy transport, etc. 9-12 Dendrimers, representing a new class of macromolecules and characterized by their treelike structure, have wide potential applications in medical science and material research. 13,14 Recently, the design, synthesis, and surface chemistry studies of amphiphilic dendrimers in Langmuir or Langmuir-Blodgett films are attracting increased attention. 15-20 One of the interesting features of am- phiphilic dendrimers is that most of them are also disklike molecules, with a flat hydrophilic dendrimer core sur- rounded by flexible hydrophobic chains. Face-on and edge- on configurations were also found in the Langmuir monolayers of these macromolecules. 19,20 In the face-on configuration, the dendrimer core lies flat on the water surface, while the hydrocarbon chains extend away from the interface. The molecules with relatively strong core- water interactions and weak core-core interactions would generally show the face-on arrangement. In the edge-on configuration, the dendrimer core sits perpendicular to the interface with part of the flexible chains submerged into the water and with other chains extended into the air. Recently, we reported the synthesis and surface chem- istry study of an amphiphilic dendrimer (PDA-PAMAM * To whom correspondence may be addressed: Tel 305-284-2282; Fax 305-284-4571; E-mail rml@umiami.ir.miami.edu. (1) Chandrasekar, S.; Ranganath, G. S. Rep. Prog. Phys. 1990, 53, 57. (2) Gregg, B. A.; Fox, M. A.; Bard, A. J. J. Am. Chem. Soc. 1989, 111, 3024. (3) Albrecht, O.; Cumming, W.; Kreuder, W.; Laschewsky, A.; Ringsdorf, H. Colloid Polym. Sci. 1986, 264, 659. (4) Ortmann, E.; Wegner, G. Angew. Chem., Int. Ed. Engl. 1986, 25, 1105. (5) Laschewsky, A. Angew. Chem. Adv. Mater. 1989, 101, 1606. (6) Karthaus, O.; Ringsdorf, H.; Tsukruk, V. V.; Wendorff, J. H. Langmuir 1992, 8, 2279. (7) Tsukruk, V. V.; Wendorff, J. H.; Karthaus, O.; Ringsdorf, H. Langmuir 1993, 9, 614. (8) Dahn, U.; Erdelen, C.; Ringsdorf, H.; Festag, R.; Wendorff, J. H.; Heiney, P. A.; Maliszewskyj, N. C. Liq. Cryst. 1995, 19, 759. (9) Boden, N.; Bushby, R. J.; Clements, J.; Jesudason, M. V.; Knowles, P. P.; Willliams, G. Chem. Phys. Lett. 1988, 152, 94. (10) Karthaus, O.; Ringsdorf, H.; Urban, C. Makromol. Chem. Macromol. Symp. 1991, 46, 347. (11) Praefcke, K.; Singer, D.; Kohne, B.; Ebert, M.; Liebmann, A.; Wendorff, J. H. Liq. Cryst. 1991, 10, 147. (12) Moller, M.; Tsukruk, V. V.; Wendorff, J. H.; Bengs, H.; Ringsdorf, H. Liq. Cryst. 1992, 12, 17. (13) Fre´chet, J. M. Science 1994, 263, 1710. (14) Zeng, F.; Zimmerman, S. C. Chem. Rev. 1997, 97, 1681. (15) Sayed-Sweet, Y.; Hedstrand, D. M.; Spinder, R.; Tomalia, D. A. J. Mater. Chem. 1997, 7, 199. (16) Schenning, A. P. H. J.; Elissen-Roman, C.; Weener, J.-W.; Barrs, M. W. P. L.; van der Gaast, S. J.; Meijer, E. W. J. Am. Chem. Soc. 1998, 120, 8199. (17) Sheiko, S. S.; Buzin, A. I.; Muzafarov, A. M.; Rebrov, E. A.; Getmanova, E. V. Langmuir 1998, 14, 7468. (18) Kampf, J. P.; Frank, C. W.; Malmstro¨m, E. E.; Hawker, C. J. Langmuir 1999, 15, 227. (19) Josefowicz, J. Y.; Maliszewskyj, N. C.; Idzik, S. H. J.; Heiney, P. A.; Mccauley, J. P. Jr.; Smith III, A. B. Science 1993, 260, 323. (20) Mindyuk, O. Y.; Heiney, P. A. Adv. Mater. 1999, 11, 341. Figure 1. Face-on and edge-on configurations of disklike molecules in Langmuir and Langmuir-Blodgett films. 7847 Langmuir 2000, 16, 7847-7851 10.1021/la0005762 CCC: $19.00 © 2000 American Chemical Society Published on Web 09/06/2000