Self-assembled multilayer films from dendrimers

Composite molecular films of(AB), type are fabricated by self-assembly of dendritic macromolecules of two adjacent generations using the electrostatic layer-by-layer deposition. Polyamidoamine dendrimers with surface amine groups for generations 4, 6, and 10 (G4, G6, G10) and carboxylic groups for generations G3.5, G5.5, and G9.5 have been used as building units. The molecular films are explored by scanning probe microscopy and X-ray reflectivity. All even generations are observed to form homogeneous, stable monolayers on a silicon surface. The thickness of a single monolayer varies with generation (molecular weight) from 1.8 nm (G4) to 2.8 nm (G6) and 5.6 nm (G10). Average thickness of a molecular layer in multilayer films is much smaller than the diameter of ideal spherical dendritic macromolecules. The model of molecular ordering of dendrimer films assumes compressed dendritic macromolecules of oblate shape with the axial ratio in the range from 1:3 to 1:6. The high interaction strength between ''sticky'' surface groups along with short range van der Waals forces and long range capillary forces are considered to be responsible for formation of compact monolayer structures. A tendency to higher spreading of high generation dendrimers observed here corresponds to the surface behavior predicted by molecular dynamic simulations.