Eur. Phys. J. E (2008) 27: 205-211
https://doi.org/10.1140/epje/i2008-10373-8

Regular Article

Aggregation of a hydrophobically modified poly(propylene imine) dendrimer

¹ Microscopy Laboratory, Oklahoma State University, 1110 S Innovation Way, 74074, Stillwater, OK, USA
² Department of Chemistry, Oklahoma State University, 74078, Stillwater, OK, USA

^* e-mail: susheng.tan@okstate.edu
^** e-mail: warren.ford@okstate.edu

Received: 26 February 2008
Revised: 23 June 2008
Accepted: 15 September 2008
Published online: 16 October 2008

Abstract

The poly(propylene imine) dendrimer DAB-dendr- (NH₂)₈ was hydrophobically modified with dodecanoyl end groups. The modified dendrimer was deposited onto mica by adsorption from solution and observed by atomic force microscopy. With the decrease of adsorption time, the modified dendrimer varied from continuous film to scattered islands. For the adsorption time of 20s the dendrimer formed a sub-monolayer thin film that contained many fractal aggregates of fractal dimension 1.80 that were > 1 μm in diameter and no more than 0.8nm thick. After 5 months at 1#1 , the initial fractal aggregates transformed into disks and other less-branched shapes with average heights of the domains of 0.6nm and 0.4nm, respectively. Formation of the fractal aggregates is explained by diffusion-limited aggregation. The slow reorganization of dendrimer molecules in the fractal aggregates occurs at a temperature well above the T_g of the dendrimer.