In situ investigation of adlayer formation and adsorption kinetics of amphiphilic surface-block dendrimers on solid substrates

The adlayer formation and adsorption kinetics of third- and fourth-generation (G3 and G4) amphiphilic surface-block dendrimers with amino and n-hexyl terminals (amino/hexyl), hydroxyl and n-hexyl terminals (hydroxyl/hexyl), and N-acetyl-D-glucosamine and n-hexyl terminals (glucosamine/hexyl) on solid substrates were investigated using atomic force microscopy, contact angle, surface plasmon resonance spectroscopy, and surface-enhanced infrared absorption spectroscopy. The amino/hexyl and hydroxyl/hexyl dendrimers formed dimer-unit layers on a solid surface, but the whole adlayer of the glucosamine/hexyl dendrimers displayed a rather flat surface, while the adlayer surface of each dendrimer was always hydrophilic. The time dependence of the adlayer formation, which was monitored in situ, obeyed two-step adsorption kinetics, namely, fast and slow adsorption steps. The adsorption amount at the adsorption equilibrium decreased in the order of hydroxyl/hexyl > amino/hexyl > glucosamine/hexyl. dendrimers, and the adsorption amount of the third-generation species was greater than that of the fourth-generation species. The linear dependence of the whole adlayer thickness on the concentration of hydroxyl/hexyl dendrimers was obtained at the equilibrium state. The molecular orientation of the hexyl chains in the adlayers was in the order of amino/hexyl > hydroxyl/hexyl > glucosamine/hexyl dendrimers.