Research on factors of influencing the preparation of 2D/3D poly(methyl methacrylate) (PMMA) colloidal crystal films at the air/water interface

In this study, PMMA microspheres were synthesized by emulsifier-free emulsion copolymerization of methyl methacrylate with sodium persulfate for the fabrication of colloidal crystal films. A rapid and facile approach to fabricate 2D or 3D PMMA colloidal crystal films at the air/water interface was developed without any complex devices. During this process, the hydrophobic PMMA microspheres were dispersed into various alcohol and self-assemble at the air/water interface to form a 2D colloidal crystal film which could further be transferred onto a solid substrate layer by layer to fabricate a 3D colloidal crystal film. The orderliness of the colloidal crystal film could be influenced by types of dispersant, the ratio of the dispersant to the PMMA microspheres emulsion and the pH of colloidal suspension. In addition, the zeta potential (ζ) of PMMA microspheres could be changed with the pH of colloidal suspension. As a result, when the ratio of n-propanol to the PMMA microspheres emulsion was 1:3 and the pH was between 4 and 5, PMMA colloidal crystal films with close-packed and high-ordered structure could be easily obtained. The morphologies and microstructures of PMMA colloidal crystal films were identified by Atomic Force microscopy (AFM) and scanning electron microscope (SEM). Their transmission spectra were measured by UV-visible spectrophotometer (UV). The results also showed that the positions of Bragg diffraction peaks were shifted to a longer wavelength with the increase of the sizes of PMMA microspheres and in good agreement with particle diameters which were theoretically calculated.