Aggregation Behaviors of Novel Amphiphilic Dendrimers at Solid-Liquid Interface

Generation 1 poly(amidoamine) dendrimer is modified with different alkyl tails. A series of novel quaternary ammonium with dendrimeric framework has been obtained, which is abbreviated as QPAMC_m (m represents the carbon number of the alkyl tail). The modified dendrimers were deposited onto the mica substrate from the solution and the aggregation properties including the morphology and the dynamic process of the adsorption were studied by atomic force microscope (AFM), x-ray photoelectron spectroscopy (XPS), and contact angle measurement. Results show that the bulk concentration and the length of hydrophobic tails significantly affect the aggregate morphology at mica-aqueous interface. With the increasing of the bulk concentration and the adsorption time the sphere aggregates transform to semi-continuous film, which is very different from conventional surfactants and linear polymers. The interaction between the hydrophobic tails might be stronger and the alkyl chains may tilt or wind when the end tail is long enough. The contact angle measurement indicates that the hydrophobicity of the solid surface adsorbed with the dendrimers vary regularly. The contact angles rise with the increasing periphery alkyl chains length of the dendrimers.