Investigation of optical and physical property in opal films prepared by colloidal and freeze-dried microspheres

Nowadays, the application of colloidal crystals as a photonic crystal template to prepare invers opal structures has been considerable in developing biosensors. The particle size distribution and polydispersity index (PDI) of polymer microspheres are highly important physical characteristics in optical properties of prepared opal films for invers opal sensors. In this study, the freeze-drying (lyophilization) effect was investigated in two different types of polymer microspheres, including polymethylmethacrylate (PMMA) and polystyrene (PS) synthesized with soap-free and surfactant agent methods with various diameters. The microspheres and three-dimensional (3D) photonic crystals (PC) opal films grown using vertical deposition method were fabricated and characterized using FTIR, DLS, SEM, and UV-vis spectral measurements. The particle sizes, PDI, SEM images and optical spectra of colloidal and freeze dried microspheres were compared. The freeze-drying process resulted in particle size and PDI increase in DLS analyses. The opal films prepared by colloidal microspheres had a more uniformity. Freeze-drying did not have significant effects on morphology of microspheres, but led to a wider stop bandwidth in the optical measurements of opal films in comparison with opal films prepared by colloidal microspheres.