Temperature-dependent formation of dendrimer islands from ring structures.

Previously unobserved high surface mobility and phase transformation phenomena in condensed, micron-scale dendrimer structures are documented using atomic force microscopy. Stratified dendrimer rings (a unique morphology resulting from microdroplet evaporation of dendrimer-alcohol solutions on mica) undergo dramatic temperature, time, and dendrimer-generation-dependent morphological changes associated with large-scale molecular rearrangements and partial melting. These transformations produce ring structures consisting of a highly stable first monolayer of the scalloped structure in equilibrium with spherical cap shaped dendrimer islands that form at the center of each pre-existing scallop (creating a "pearl necklace" structure).

Dendrimer pattern formation in evaporating drops.

The redistribution of organic solutes during drop evaporation is a nanoscale self-assembly process with relevance to technologies ranging from inkjet printing of organic displays to synthesis of biosmart interfaces for sensing and screening. We have used solutions of dendrimer molecules with incrementally varying terminal site chemistry to explore whether the condensed dendrimer patterns resulting from microdroplet evaporation sensitively depend on, and are characteristic of, the surface chemistry of the solute molecules. This hypothesis has been experimentally confirmed by comparing the behavior of microdroplets of G4, G4-25%C12, and G4-50%C12 dendrimers dissolved in pentanol and deposited on mica substrates.