Silvia Adriana Estrada Alvarez

The natural occurrence of precious opals, consisting of highly organized silica particles, has prompted interest in the synthesis and formation of these structures. Previous research has shown that a highly organized photonic crystal (PhC) array is only possible when it is based on a low polydispersity index (PDI) sample of particles. In this study, a solvent-only variation method is used to synthesize different sizes of silica particles (SiPs) by following the traditional sol-gel Stöber approach. The controlled rate of the addition of the reagents promoted the homogeneity of the nucleation and growth of the spherical silica particles, which in turn yielded a low PDI. The opalescent PhC were obtained via self-assembly of these particles using a solvent evaporation method. Analysis of the spatial statistics, using Voronoi tessellations, pair correlation functions, and bond order analysis showed that the successfully formed arrays showed a high degree of quasi-hexagonal (hexatic) organization, with both global and local order. Highly organized PhC show potential for developing future materials with tunable structural reflective properties, such as solar cells, sensing materials, and coatings, among others.

The mimicking and fabrication of gecko toe pads structures can lead to limitless applications. In this study, polypropylene (PP), polyethylene (PE) and polycaprolactone (PCL) nano‐fibers are fabricated using a porous membrane as template. The surface characteristics and physical properties of the samples yield different geometries, which determine the wetting and adhesive properties of the fabricated samples. Oriented and wave‐like shapes fibers present the Gecko effect, thanks to their ability to comply and hydrophobic asperities that uphold the water droplet when the wetting properties were tested. The samples are also found to be self‐cleaning due to their high contact angles and low contact angle hysteresis. Adhesion tests results prove that the samples are high reversible adhesion with the ability to stick to smooth surface in a dry and underwater environment. The adhesion on the samples can be enhanced with a double fibril layer or buckling property. They adhere better when the surface is not hydrophilic. By behaving in similar way as the real geckos, the results of this study show that the fabricated samples effectively present the Gecko effect. POLYM. ENG. SCI., 57:283–290, 2017. © 2016 Society of Plastics Engineers