Domain-Size Effects in Optical Diffraction from Polymer/Composite Microparticles

Poly(ethylene glycol) [PEG] microparticles were doped with ceramic or latex nanoparticles in order to examine domain-size and refractive index effects of nanometer-sized guest inclusions on two-dimensional diffraction patterns. Composite microparticles were examined for different inclusion sizes and polymer/nanoparticle weight ratios in order to determine the size and number-density threshold of detection for guest nanoparticles within the polymer host as indicated by fringe distortion in 2-D angular scattering. PEG host particles having a 10 μm (nominal) diameter were formed with three different guest nanoparticles (Al₂O₃, TiO₂, and latex nanospheres with respective sizes of 46, 29, and 14 nm). For the ceramic nanoparticle inclusions, distortion was observed at relative guest-host weight fractions of 5-10%. For the 14 nm latex inclusions, no distortion was observed at any weight fraction. A perturbation method was used to simulate the effect of nanometer-size inclusions on 2-D optical diffraction from polymer host microparticles and to suggest how the distortions should vary with inclusion size, refractive index, and number.