Dendrimers on Surfaces Conformational Behaviour

The preparation of thin films and layers from dendrimers by self-assembly is a topic of great current interest since it allows the construction of functional interfaces that use specific dendritic properties such as size, shape, porosity, end-group density and multifunctionality. It is also an area of research that benefits substantially from the flexible character intrinsic to most dendrimers. 

Predictions made by Mansfield et al. regarding the surface behaviour of dendrimers were confirmed by Tsukruk et al. who used poly(amidoamine) (PAMAM) dendrimers (generations G3.5-G10) to construct self-assembled monolayers (SAMs) [34,35]. PAMAMs of two adjacent generations with surface amine and carboxylic acid end-groups, respectively, were used in an electrostatic 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

Depending on the strength and type of interaction between the dendrimer and the surface, they can flatten out almost completely. Although the unique spherical shape of the dendrimer is very often lost in self-assembled films, other specific properties such as multifunctionality, porosity etc. are retained. This important feature has led to the birth of a new and exciting area of research functional dendritic surfaces, which will be discussed in the next section. 

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