Solid-like states of a dendrimer liquid displayed by scanning force microscopy

Adsorption and aggregation of carbosiloxane dendrimers on mica and pyrolytic graphite were investigated by scanning force microscopy (SFM). The aggregation process started from (i) single molecules which coagulated to (ii) clusters and (iii) fluid droplets followed by formation of (iv) a complete layer on the solid substrate. The molecules were displayed as a globular particle with a diameter of about 2.5 nm. Tapping SFM of the liquid was possible due to the fact that the dendrimer undergoes a transition to a viscoelastic state below the tapping frequency of about 360 kHz. Dynamic shear compliance experiments have shown a plateau of 5 · 10⁻⁷ Pa⁻¹ around this frequency. Dendrimer droplets slowly spread into polygonal lamellae with a thickness of two molecular layers. The structures indicate a rather regular dense packing of the globular molecules.