Self-Assembled Multilayer Films from Dendrimers

Abstract

Composite molecular films of (AB)x 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.

Layer-by-layer self-assembly of hydrophobically modified polyelectrolytes

“…Also, the very thin average thicknesses suggest a complete decoiling of the polymers upon adsorption, with micelle-like hydrophobic domains being absent. An analogous extended, flat conformation was reported for adsorbed cationic dendrimers 28) . Nevertheless, the roughnesses of the multilayers are rather high, increasing with the number of deposition cycles for a given system, but also with the hydrophobic character of the polycation, up to the range of 2.0 -4.0 nm.…”

Probing the validity of the Derjaguin approximation for heterogeneous colloidal particles

“…At these conditions the dendrimers are fully charged 29 and are known to adsorb strongly to oppositely charged surfaces. 30,31 The adsorption has reached saturation after 12 h. When such a dendrimer-coated surface is in contact with pure electrolyte solution, the adsorption is irreversible within the experimental time window. This fact has been verified under similar conditions by AFM imaging and time-resolved reflectometry.…”

Assembling hyperbranched polymerics

“…[78][79][80][81][82] Relevant surface layers from dendrimers, which are popular, regular, highly branched polymers, have been fabricated and studied since mid-1990s. 23,[83][84][85][86][87] For instance, Xiao and coworkers have created thin films from SiCl 3 -terminated dendrons on mica. 88 Van Duijvenbode and coworkers fabricated surface layers from five generations of 1,4-diaminobutane poly(propylene imine).…”