Resumen de Fast responsive photochromic materials through nanoemulsion entrapment
Along this thesis, an optically transparent photochromic material with fast and liquid-like kinetic response has been developed, and the methodology to produce said material is described herein. This technology is based on the nanoemulsion entrapment (NEE) technique, in which a nanoemulsion is first formed and stabilized by a film-forming polymer, and then the solvent of the continuous phase is removed, to generate a film containing the emulsion droplets entrapped in it.
Having the photochromic dyes dissolved in the dispersed liquid phase of the droplets ensures minimal steric hindrance for the dye to isomerize and therefore the fastest photochromic kinetics for the dye used (i.e. liquid-like behavior), while the continuous polymeric film provides a solid platform, which is the most convenient for the majority of applications. Moreover, the NEE films are visually transparent (> 90 %T), since the dispersed droplets are reduced to the nanoscale size (< 100 nm), by either ultrasonic irradiation or high-pressure homogenization, minimizing light scattering.
It has been demonstrated that the properties of the NEE films are easily tunable to match the key requirements of different applications. By simply changing the photochromic dyes it is possible to control the photoinduced colors, the coloration/discoloration rates and the color intensity of the activated state. The coloration and discoloration rates can be finely tuned by substituting the hydrophobic oil of the droplets. The modification of the polymeric matrix allowed to withstand moisture and higher temperatures exposure.
The production of NEE films was scaled up to the 200 g. Some working prototypes for potential industrial applications were produced such as eyewear, smart windows, car windshields and helmet visors, and are presented at the end of this thesis.
