Raspberry-like and other hexagonal close-packed morphologies of P(St-MMA-AA) particles obtained from different emulsifiers for photonic applications.

A facile one-pot synthesis of Poly(Styrene-methyl-methacrylate-acrylic acid) P(St-MMA-AA) terpolymers by soap seeded emulsion polymerization was examined. Raspberry-like and hexagonal close-packed morphologies were conveniently obtained using Cetyltrimethylammonium bromide (CTAB), Sodium dodecyl sulphate (SDS) and Gum arabic (GA) emulsifiers. The resultant colloidal latex samples were used to fabricate coloured tunable photonic crystals via vertical deposition process. The results showed that the emulsifiers used effectively reduced the polydispersity index (PDI) and zeta potential of the terpolymer samples (Ter-PSDS, Ter-PGA and Ter-PCTAB 0.021, 0.097 and 0.076; –36.20, –35.60 and –32.80, respectively). Thus, the interfacial tension between particles that promote the formation of the stable nanosized photonic crystals is also reduced. The low PDI values are clear indication of monodispersity of the terpolymer samples. Varying the choice of emulsifiers also resulted in changes in the particles sizes as well as the resultant morphologies. The particles diameters of 117.15, 209.20 and 315.00 nm were obtained for Ter-PSDS, Ter-PGA and Ter-PCTAB, respectively. The results showed that Ter-PSDS was the most stable of all terpolymers examined. The fabricated photonic crystals were observed to reflect different wavelengths (Iridescent colours) as the observation angles changed. This could be due to the bandgap resulting from the different morphologies associated with the different emulsifiers. The variation in the colour reflectance with change in the observation angle confirms the photonic potential of the synthesized P(St-MMA-AA) crystals.