Synthesis and Characterization of Colloidal Crystal Array of Polystyrene-Hydrophilic Monomer Microgels

Abstract

We developed a new photonic colloidal crystal array based on hydrophobic monomer styrene (St) and hydrophilic monomers acrylic acid (AAc), methacrylic acid (MAc), and itaconic acid (IAc) by free radical emulsion polymerization method. These St/AAc, St/Mac, and St/IAc nanoparticles were characterized with respect to particle size by SEM. Reflectance microscopy was utilized to monitor structural changes during the self-assembly of monodispersed colloidal systems at room temperature. Three different monomers gave three different particle sizes, 159.9 nm, 280.7 nm, and 255.8 nm for St/AAc, St/Mac, and St/IAc microgel, respectively. Difference in particle size arises due to the change in monomer molecular weight, 72.06, 86.09, and 130.1 for AAc, Mac, and IAc respectively. These monodispersed, spherical colloidal particles that rapidly self-assemble via simple solvent evaporation to form 3-D colloidal crystals are both robust and uniformly diffractive. SEM analysis revealed the hexagonal particle shape of St/AAc and square shape of St/IAc. As crystals dry, they assist in particle self-assembly to form an ordered structure. These dried, colloidal crystal arrays exhibit Bragg diffraction, which can be modified by changing monomer types acrylic acid, methacrylic acid, and itaconic acid. This unique approach can be used as processable emulsions, which can be used for the preparation of materials for chemical sensors. These microgels if functionalized with calcium could be used as a potential sensor for organophosphate nerve agent like paraoxon.