Self-assembled particle monolayers on polyelectrolyte multilayers: particle size effects on formation, structure, and optical properties

Monolayers of charged polystyrene latex particles ranging in size from 100 nm to 10 mu m were deposited on oppositely charged polyelectrolyte multilayers (PEMs) by electrostatic interactions and capillary forces. Ultrathin PEMs (similar to 30 nm) formed on a glass slide provided an excellent underlying adhesive layer. As the sample surface was being dried, strong capillary forces between particles resulted in a unique pattern of particle monolayers (i.e., two-dimensional (2-D) particle aggregates). The resulting topographical structure of the coatings strongly influenced the transmission of visible light through the slides. The total and specular transmittances showed three different characteristics as a function of particle size: (1) anti-reflection, when the particle diameter (D-paticle) is around a quarter of the wavelength of the incident visible light (D-particle similar to lambda(vis)/4), (2) diffraction, when the Dparticle is equivalent to the wavelength of the incident beam (D-particle similar to lambda(vis)), and (3) diffusive scattering when the D-particle is bigger than the wavelength of the incident beam (D-particle similar to lambda(vis)). Additionally, for the first time, the monolayer coverage and fractal-dimension analyses have been reported over a wide range of particle sizes. Functional groups present in these coatings allow further customization via chemical modification. (c) 2005 Elsevier B.V. All rights reserved.