FACILE SURFACE MODIFICATION OF COLLOIDAL PARTICLES USING BILAYER SURFACTANT ASSEMBLIES - A NEW STRATEGY FOR ELECTROSTATIC COMPLEXATION IN LANGMUIR-BLODGETT-FILMS

Preliminary investigations have recently indicated that interdigitated bilayer assemblies of fatty acid molecules form spontaneously on coll oidal silver particle surfaces while such bilayer structures are not o bserved on planar silver films. In this paper, this problem is probed further through contact angle and quartz crystal microgravimetry measu rements of monolayer formation of lauric acid molecules on well-define d hydrophobic monolayers (formed from octadecanethiol chemisorbed on g old films) as a function of solution pH. The repulsive interaction bet ween the ionized carboxylic acid groups in the lauric acid molecules p revents the formation of bilayer assemblies on planar surfaces. Howeve r, nanoscale surface curvature of colloidal particles permits interdig itation of the hydrocarbon chains in the bilayers, thereby maximizing the hydrophobic interaction as well as considerably reducing the elect rostatic repulsive interactions of the headgroups, leading to stable b ilayer assemblies. The strategy based on bilayer formation on colloida l particles is flexible and is used to derivatize colloidal silver par ticles with carboxylic acid and amine functional groups and thereafter electrostatically immobilize them at the air-hydrosol interface using the conjugate Langmuir monolayer. Good quality multilayer colloidal p article films can be deposited by the Langmuir-Blodgett technique, ind icating that the bilayer assemblies on the colloidal particles are qui te robust. This novel approach considerably extends the scope for the generation of nanoscale architectures using self-assembly of surface-m odified colloidal particles.