Control of Specular and Diffuse Reflection of Light Using Particle Self-Assembly at the Polymer and Metal Interface


  • We would like to acknowledge Dr. Michael F. Rubner and Prof. Paula T. Hammond at MIT for the discussion of the work. This work was funded by the NSF (CTS-0609164), the AFOSR (Air Force Equipment Grant No. FA 9550-06-1-0417), the Michigan Economic Development Corporation, and the MSU foundation.


We present a novel method of controlling the specular and diffuse reflection of light by the electrostatic deposition of a spherical particle monolayer followed by electroless plating. Charged polystyrene colloidal particles, ranging in size from 100 nm to 5 μm, were adsorbed from solution onto oppositely charged polyelectrolyte multilayers (PEM). The monodisperse particle monolayers were coated with nickel in a two-step electroless plating process using palladium catalysts. These surfaces can be used as diffusive metal reflectors with a uniformly controlled surface roughness due to the uniform size of deposited particles. In addition, the self-assembled particles at the polymer and metal interface deflected the internal stresses that build-up at the interface while the metal was being deposited. This allowed a thicker metal film to be deposited before delamination occurred. A UV-VIS spectrometer with movable fiber optic cables was employed to characterize the optical properties of the reflectors. The optical fibers permit versatile and precise measurements of specular and diffuse reflectance. By measuring the angular dependent reflectance, we demonstrate how to estimate the distribution of reflected light from the nickel coated surface and how to calculate the ratio of specular and diffuse reflection in the total reflected light. Optical measurements of our nickel samples showed that this approach could be used to control the portion of diffuse reflection from 8.25 to 59.97 %. Additionally, a quartz crystal microbalance was employed to study the electroless nickel plating rate on PEM. Our proposed method is simple, cost-effective and convenient for mass production because the process consists of a series of simple immersion steps without vacuum technology or special equipment.