Dec
28

Nanopatterning with dendrimers

Author Rémi Longtin    Category Nanopatterning     Tags , ,

Presentation

The following section is a short introduction to my most recent research (2007 to 2009) at the University of Geneva in the laboratory for colloids and surface chemistry.

G10 PAMAM dendrimer on silicaThe adsorption of macromolecules at the solid-liquid interface is a very common yet complicated phenomenon. One has simply to think of what happens when a drop of blood falls on a surface. Blood is a complex colloidal system. The fluid contains several macromolecules (proteins, biopolymers) as well as ions (Fe, K, Cl, Na etc.) and other cells all interacting with each other and with the surface. Preventing or promoting the adsorption of blood (or its specific constituents) to a surface may be critical in some biomedical applications. This example illustrates how macromolecular adsorption is ubiquitous, yet can be of great importance for both industry and fundamental science.

In terms of nano-technological applications, charged macromolecules from solutions can be used to pattern mineral surfaces. Typically, an interface will acquire a charge when immersed in a solution, water in this case. Similarly, the macromolecule’s ionizable functional groups can take or release protons, thus have a pH-dependent charge. When the charges of both molecule and surface have opposite signs and are of sufficient magnitude, adsorption via electrostatic interactions occurs.

Adsorption of PAMAM dendrimers

A fair deal of research in our lab deals with cationic poly(amidoamine) dendrimers (Fig.1). These hyperbranched synthetic polymers are ideal molecules for surface patterning. They are globular in shape, adsorb rapidly either reversibly or irreversibly at interfaces[1] and are available in a wide range of sizes depending on the generation.

Figure 1: Structure of poly(amido amine) dendrimers (PANAM)

Figure 1: Structure of poly(amido amine) dendrimers (PANAM)

Adsorption of PAMAM dendrimers on silica is the result of strong electrostatic interactions between the charged amine groups (NH3+) on the dendrimer and the dissociated silanol (Si-O-) sites on the surface. Hydrogen bonding is also believed to contribute to the adsorption (Fig.2). The dendrimers tend to flatten once at the interface so as to maximize surface-segment binding.

Figure 2: Schematic representation of PAMAM dendrimer adsorption on silica

Figure 2: Schematic representation of PAMAM dendrimer adsorption on silica

The spontaneously organization of dendrimers at the silica-water interface is not random but rather liquid-like as can be seen from AFM imaging (Fig.3).

Figure 3: AFM image of G10 PAMAM dendrimer on silica

Figure 3: AFM image of G10 PAMAM dendrimer on silica

The inter-dendrimer spacing depends on the electrostatic repulsions, which can be modulated via the pH and ionic strength of the solution[3]. Some degree of control over the monolayer’s structure is achievable as feature dimensions (height, width) depend on the selected dendrimer generation. Therefore solid substrates can patterned at the nanometer scale using adsorbed dendrimers[4]. The reader should consult the cited articles for more details.

Literature

[1] R. Longtin, P. Maroni, M. Borkovec, Langmuir 2009, 25, (5), 2928-2934

[2] I. Popa, R. Longtin, P. Maroni, G. Papastavrou, M. Borkovec, CHIMIA International Journal for Chemistry 2009, 63, 279

[3] B. P. Cahill, G. Papastavrou, G. J. M. Koper, M. Borkovec, Langmuir 2008, 24, (2), 465-473

[4] R. Pericet-Camara, B. P. Cahill, G. Papastavrou, M. Borkovec, Chemical Communications 2007, 266-268.

Author: Remi Longtin

1 Comment to “Nanopatterning with dendrimers”

  • rohit Friday October 8th, 2010 at 12:45 AM

    Is it a conceptual design for polymer free coating process?

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