Mono- and multilayers of mesogen-substituted carbosilane dendrimers on mica

Self-assembled ultrathin (5-15 nm) films of carbosilane dendrimers with mesogenic units on the periphery, obtained after deposition on mica surfaces, have been studied with atomic force microscopy. Dendritic polymers with 12, 36, and 108 mesogenic cholesteryl end groups, first, second, and third generation, respectively, were employed. Solvent casting was used to generate the films. At high concentrations of the dendrimers in solution, flat, homogeneous films of 2-4 dendrimer layers were found. For low dendrimer concentrations, a single dendrimer monolayer exhibiting an irregular cellular pattern of holes was observed. The thickness of the monolayer correlated well with the diameter of the dendrimers and with wide-angle X-ray scattering results obtained on crystalline powders. Annealing of the films of G1 and G2 in the liquid crystalline phase caused reorientation of the molecules at the surface. The third-generation dendrimer with 108 end groups (G3), the periphery of which is densely packed with mesogens, behaved differently and did not show dewetting or reorientation upon annealing, which is attributed to lower molecular mobility.