Photonic Crystals

The tail of a peacock is an example of the unparalleled ability of nature to create exquisite ordered structures with unique functionalities. The intense and fiery blue and green we see on the tail comes from a nanoscale structure of the feathers that allows light of a specific wavelength to be amplified and for other wavelengths to be blocked. The colour that arises from photonic assemblies is called ‘structural colour’ and inspired the roman poet, Lucretius (99-55 B.C.) [73] There is a wealth of photonic nanostructures that have been synthesised, including the inverse opal arrays of Joanna Aizenberg [74, 75] and amphiphilic magnetic NP [76]. In the work by Dorvee and co-workers, controlled manipulation of amphiphilic, superparamagnetic, iron oxide fluid droplets was presented [76]. This manipulation involves, in general, the control of small volumes of fluids. It is an important challenge in microfluidics [77] because it represents a key requirement for various assays [78].

In previous works, one-dimensional photonic crystals have been constructed using porous silicone and demonstrated to have amphiphilic character. Due to their amphiphilic behaviour, if placed in a two-phase liquid-liquid system, for example, dichloromethane- water, they tend to accumulate and align spontaneously at the interface. Dorvee and co-workers demonstrated that superparamagnetic NP of iron oxide (in the oxidation state and crystal structure of magnetite) could be incorporated into a porous nanostructure. Also, they could be manipulated through an external magnetic field, with the optical reflectivity spectrum of the fluid displaying a peak which is used to identify the droplet, with the latter also used as a medium for carrying out a chemical reaction. For the synthesis of the droplet, the particle film is hydrosilylated with 1-dodecene [79]. In general, liquid-liquid interfaces have been employed widely for the synthesis of mesoporous materials (see Li and co-workers for a review of published work [80]).