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 μm were deposited on oppositely charged polyelectrolyte multilayers (PEMs) by electrostatic interactions and capillary forces. Ultrathin PEMs (∼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 (Dparticle) is around a quarter of the wavelength of the incident visible light (Dparticle ∼ λvis/4), (2) diffraction, when the Dparticle is equivalent to the wavelength of the incident beam (Dparticle ∼ λvis), and (3) diffusive scattering when the Dparticle is bigger than the wavelength of the incident beam (Dparticle ∼ λvis). 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.