No abstract

In nature, in order to prevent attention from predators, the eyes of night-flying moths have evolutionarily developed an antireflective ability. The surfaces of their eyes are covered with a layer of a sub-wavelength structure that eliminates reflections of visible light. This layer allows the eyes of moths to escape detection in darkness, without reflections that could reveal the position of the moths to potential predators. In this study, we proposed a novel procedure for manufacturing a non-close-packed polystyrene (PS) nanosphere monolayer by combining the Langmuir-Blodgett (LB) deposition technique and oxygen plasma treatment. An antireflective structure was replicated from the sub-wavelength structure of moth eyes onto the surface of a glass substrate by nano-imprinting lithography; the structure also displayed hydrophobic properties. The Fresnel reflection of the replicated sub-wavelength structure is near the theoretical prediction from the effective medium theory model. The biomimetic moth-eye structure can be applied to solar cells, monitors, light-emitting diodes, and other optical devices in the future.

No abstract

Polystyrene (PS) opal and titania (TiO 2 ) inverse opal films were fabricated by the self-assembly colloidal crystal template technique. Based on Bragg's law, these sensors were used to detect the different concentrations of ethanol solution. The results indicated that TiO 2 inverse opal films were advantageous over PS opal film for detecting the ethanol concentration. TiO 2 inverse opal films sintered at 600˝C retained the highest sensitivity for ethanol concentration identification, since the anatase phase was transformed into the rutile phase, which resulted in an enhancement of the refractive index, i.e., an increase in the amount of the red shift.

Emulsifier-free emulsion polymerization was employed to synthesize polystyrene (PS) microspheres, which were then self-assembled into an ordered periodic structure. A photochromic film was formed by adding polydimethylsiloxane (PDMS) around the self-assembly of PS microspheres on a PDMS substrate. During polymerization, the PS microspheres shrunk depending on the amount of the hydrophilic comonomer, sodium 4-styrenesulfonate (NaSS). Variation in structural color was strongly affected by the size of the PS microspheres. Scanning electron microscopy was used to observe the surface and cross sections of the self-assembled microspheres. Results showed that the order and stacking thickness of microspheres were dependent on the drawing rate of the substrate and suspension concentration. High-transmittance photochromic films could be prepared when the drawing rate was lower than 1 μm/s and the suspension concentration was 20 wt %. PDMS surrounding the vacant space between regularly arranged PS microspheres could not only protect them but also increase the degree of matching between the refractive indices of PS and PDMS. The stability of the reflected structural color increased, and the optical transmittance of the photochromic film approached 95% after PDMS was poured between the PS microspheres. A special pattern could be designed and embedded inside the photochromic film. The PS/PDMS photochromic films can also be applied in decorative painting as well as in security devices, color-changing false nails, and privacy filters.