Abstract
Polymethylmethacrylate (PMMA) microspheres were synthesized by surfactant-free emulsion polymerization. These microspheres were used to obtain opals by the self-assembly method. Monomer and initiator quantities were varied systematically to monitor the size of PMMA microspheres. From SEM and DLS measurements, a trend was observed showing as the monomer and initiator amounts increased the average diameter of PMMA microspheres increased except when a minimum monomer amount was reached, for which the size of the microspheres remained practically constant. Diffuse reflectance spectra were processed by the Kubelka–Munk treatment to estimate the energy band gap (Eg) of the PMMA microspheres. It was found that PMMA microspheres present an indirect transition. From SEM micrographs, it is seen that PMMA opals photonic crystals are formed by microspheres in a uniform periodic face-centered cubic (fcc) array. Variable-angle specular reflectance spectra show that the opals possess a pseudo photonic band gap (PBG) in the visible and near-IR regions. Furthermore, it was found that PBGs shift towards larger wavelengths as the average diameter of the PMMA microspheres increases.
Highlights
Periodicity in the refraction index gives rise to diffraction effects of photons on dielectric lattice planes, resulting in a photonic band gap (PBG) or a stop band that inhibits a range of wavelengths from propagating through the crystal [2]
PMMA microspheres were synthesized by means of surfactant-free emulsion polymerization method reported by E
PMMA microspheres were synthesized by means of the surfactant-free emulsion polymerization method by systematically varying the amount of initiator and the amount of monomer
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The PMMA synthesis method most used is the surfactant-free emulsion polymerization (SFEP) because the obtained colloidal spheres have good monodispersity and clean surface features [12] In this process, the monomer is dispersed in water and, in the presence of a free radical initiator, the polymerization is started. To obtain a large particle size, the amount of monomer must be increased, the amount of initiator must be decreased, or the reaction must be carried out at low temperature [1,6,18,19,20,21] These results are well established in the literature, a careful review of the synthesis of PMMA and other polymers using the SFEP method shows inconsistencies when the amount of initiator is varied [6]. The results can provide insight into the properties of PMMA
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