Amphiphiles with a dendritic structure are attractive materials as they combine the features of dendrimers with the self-assembling properties and interfacial behavior of water-air affinities. We have synthesized three generations of polyester dendrimers and studied their interfacial properties on the Langmuir films. The behavior obtained was, as a rule, the lowest generation dendrimers behaving like traditional amphiphiles and the larger molecules presenting complicated isotherms. The Langmuir films of these compounds have been characterized by their surface pressure versus molecular area ( ) and Brewster angle microscopy (BAM) observations. 1. Introduction Various synthetic routes and structural modifications of dendrimers have been proposed, and several of their properties are now understood [1–4]. Therefore, potential applications of dendrimers at surfaces are clearly growing, for example, in surface-based catalysts [5, 6]; in the synthesis and stabilization of metal nanoparticles or as drug delivery supports [7]. Nevertheless, the general principles determining molecular conformation at the air-water interface are still under study [8–10], with unsolved questions such as the differences in the molecular shape near the interface and their relationship to the three-dimensional; the importance of the chemical functionalities of the different parts of the molecule; the shape of the formed monolayers, and so forth. So far, the knowledge of dendrimer structure in Langmuir films (at the air-water interface) comes largely from pressure-area ( - ) measurements, which are however open to multiple interpretations [11–16]. During the past few years there has been a considerable interest in the use of dendrimers as surface and interface active materials. The preparation of Langmuir films from amphiphilic dendrimers or monodendrons has been investigated by several research groups [17–21], since the Langmuir technique helps to access valuable information about the behavior of dendrimers at the air-water interface. Previous publications showed possible approaches to achieve surface activity for dendritic molecules, but few of them have described Langmuir films obtained from dendritic molecules [22–25] and their application. In this paper, we report the incorporation in Langmuir films of three generations of polyester dendrimers, in order to contribute to the understanding of the supported dendrimer properties and their behavior. 2. Experimental 3,5-Dihydroxybenzoic acid (DHBA) (97+%), 1,3,5-tris(2-hydroxyethyl) cyanuric acid (THECA) (97+%), and p-toluenesulfonic
References
[1]
D. A. Tomalia, H. Baker, J. Dewald et al., “Dendritic macromolecules: synthesis of starburst dendrimers,” Macromolecules, vol. 19, no. 9, pp. 2466–2468, 1986.
[2]
A. W. Bosman, H. M. Janssen, and E. W. Meijer, “About dendrimers: structure, physical properties, and applications,” Chemical Reviews, vol. 99, no. 7, pp. 1665–1688, 1999.
[3]
M. Ballauff and C. N. Likos, “Dendrimers in solution: insight from theory and simulation,” Angewandte Chemie—International Edition, vol. 43, no. 23, pp. 2998–3020, 2004.
[4]
G. J. M. Koper, M. H. P. van Genderen, C. Elissen-Román, M. W. P. L. Baars, E. W. Meijer, and M. Borkovec, “Protonation mechanism of poly(propylene imine) dendrimers and some associated oligo amines,” Journal of the American Chemical Society, vol. 119, no. 28, pp. 6512–6521, 1997.
[5]
A. Mansour, T. Kehat, and M. Portnoy, “Dendritic effects in catalysis by Pd complexes of bidentate phosphines on a dendronized support: heck versus carbonylation reactions,” Organic and Biomolecular Chemistry, vol. 6, no. 18, pp. 3382–3387, 2008.
[6]
Y. N. Niu, Z. Y. Yan, G. Q. Li et al., “1,2,3-Triazole-linked dendrimers as a support for functionalized and recoverable catalysts for asymmetric borane reduction of prochiral ketones,” Tetrahedron Asymmetry, vol. 19, no. 8, pp. 912–920, 2008.
[7]
R. Redón and N. G. García Pe？a, “Triazine based dendrimers: their applications as drug delivery agents,” in Triazines: Synthesis, Applications and Toxicity, R. Bhai Patel and R. Malhotra, Eds., Chemical Engineering Methods and Technology Series, Nova Sciencie, Hauppauge, NY, USA, 2012.
[8]
A. Su, S. Tan, P. Thapa, B. N. Flanders, and W. T. Ford, “Highly ordered langmuir-blodgett films of amphiphilic poly(propylene imine) dendrimers,” Journal of Physical Chemistry C, vol. 111, no. 12, pp. 4695–4701, 2007.
[9]
B. M. Rosen, D. A. Wilson, C. J. Wilson et al., “Predicting the structure of supramolecular dendrimers via the analysis of libraries of AB3 and constitutional isomeric AB2 biphenylpropyl ether self-assembling dendrons,” Journal of the American Chemical Society, vol. 131, no. 47, pp. 17500–17521, 2009.
[10]
B. P. Cahill, G. Papastavrou, G. J. M. Koper, and M. Borkovec, “Adsorption of poly(amido amine) (PAMAM) dendrimers on silica: Importance of electrostatic three-body attraction,” Langmuir, vol. 24, no. 2, pp. 465–473, 2008.
[11]
W. J. Pao, M. R. Stetzer, P. A. Heiney, W. D. Cho, and V. Percee, “X-ray reflectivity study of langmuir films of amphiphilic monodendrons,” Journal of Physical Chemistry B, vol. 105, no. 11, pp. 2170–2176, 2001.
[12]
K. L. Genson, D. Vaknin, O. Villacencio, D. V. McGrath, and V. V. Tsukruk, “Microstructure of amphiphilic monodendrons at the air-water interface,” Journal of Physical Chemistry B, vol. 106, no. 43, pp. 11277–11284, 2002.
[13]
X. Zhai, S. Peleshanko, N. S. Klimenko et al., “Amphiphilic dendritic molecules: hyperbranched polyesters with alkyl-terminated branches,” Macromolecules, vol. 36, no. 9, pp. 3101–3110, 2003.
[14]
M. Ornatska, S. Peleshanko, K. L. Genson, B. Rybak, K. N. Bergman, and V. V. Tsukruk, “Assembling of amphiphilic highly branched molecules in supramolecular nanofibers,” Journal of the American Chemical Society, vol. 126, no. 31, pp. 9675–9684, 2004.
[15]
S. Peleshanko, R. Gunawidjaja, S. Petrash, and V. V. Tsukruk, “Synthesis and interfacial behavior of amphiphilic hyperbranched polymers: poly(ethylene oxide)-polystyrene hyperbranches,” Macromolecules, vol. 39, no. 14, pp. 4756–4766, 2006.
[16]
S. Peleshanko and V. V. Tsukruk, “The architectures and surface behavior of highly branched molecules,” Progress in Polymer Science, vol. 33, no. 5, pp. 523–580, 2008.
[17]
G. Sui, M. Micic, Q. Huo, and R. M. Leblanc, “Synthesis and surface chemistry study of a new amphiphilic PAMAM dendrimer,” Langmuir, vol. 16, no. 20, pp. 7847–7851, 2000.
[18]
A. P. H. J. Schenning, E. Peeters, and E. W. Meijer, “Energy transfer in supramolecular assemblies of oligo(p-phenylene vinylene)s terminated poly(propylene imine) dendrimers,” Journal of the American Chemical Society, vol. 122, no. 18, pp. 4489–4495, 2000.
[19]
J. F. Nierengarten, J. F. Eckert, Y. Rio, M. P. Carreoón-Castro, J. L. Gallani, and D. Guillon, “Amphiphilic diblock dendrimers: synthesis and incorporation in Langmuir and Langmuir-Blodgett films,” Journal of the American Chemical Society, vol. 123, no. 40, pp. 9743–9748, 2001.
[20]
H. K. Shin, J. M. Kim, Y. S. Kwon, E. Park, and C. Kim, “Optical behavior and surface morphology of the azobenzene functionalized dendrimer in Langmuir and Langmuir-Blodgett monolayers,” Optical Materials, vol. 21, no. 1–3, pp. 389–394, 2002.
[21]
K. Tanaka, S. Dai, T. Kajiyama, K. Aoi, and M. Okada, “Aggregation states and molecular motion in amphiphilic poly(amido amine) dendrimer monolayers on solid substrates,” Langmuir, vol. 19, no. 4, pp. 1196–1202, 2003.
[22]
S. B. Jung, C. Kim, and Y. S. Kwon, “Fabrication and electrical properties of dendritic macromolecule thin films based on metal complexes,” Thin Solid Films, vol. 438-439, pp. 27–32, 2003.
[23]
M. Liebau, H. M. Janssen, K. Inoue et al., “Preparation of dendritic multisulfides and their assembly on air/water interfaces and gold surfaces,” Langmuir, vol. 18, no. 3, pp. 674–682, 2002.
[24]
A. S. Costa and T. Imae, “Morphological investigation of hybrid langmuir—blodgett films of arachidic acid with a hydrotalcite/dendrimer nanocomposite,” Langmuir, vol. 20, no. 20, pp. 8865–8869, 2004.
[25]
S. R. Lee, D. K. Yoon, S. H. Park et al., “Surface ordering of a perfluorinated, self-assembled, dendrimer on a water subphase,” Langmuir, vol. 21, no. 11, pp. 4989–4995, 2005.
[26]
S. H. Mansour, N. N. Rozik, K. Dirnberger, and N. E. Ikladious, “Hyperbranched polyesters based on polycondensation of 1,3,5-tris(2-hydroxyethyl) cyanuric acid and 3,5-dihydroxybenzoic acid,” Journal of Polymer Science A, vol. 43, no. 15, pp. 3278–3288, 2005.
[27]
C. J. Hau, D. Yan, and Z. Wang, “Preparation and characterization of fluorescent hyperbranched polyether,” Reactive and Functional Polymers, vol. 58, no. 1, pp. 65–72, 2004.
[28]
J. N. Israelachvili, Intermolecular and Surface Forces, Academic Press, San Diego, Calif, USA, 2nd edition, 1992.
