Materials fotocròmics de resposta ràpida mitjançant atrapaments de nanoemulsió

Hèctor Torres Pierna

Claudi Roscini

L'objectiu d'aquesta tesi era explorar el potencial dels materials fotocròmics nanoestructurats com a recobriments fotoprotectors per a ulleres per proporcionar comoditat a l'usuari i per a ulleres intel·ligents que estalvien energia. Inicialment, els colorants fotocròmics es dissolien dins de les nanocàpsules de nucli líquid. Les càpsules es dispersaven en pel·lícules de polímer que es podien integrar en productes comercials. Tanmateix, mantenir la transparència adequada en integrar les càpsules va resultar molt difícil, fins i tot quan les càpsules eren a nanoescala, a causa de l'agregació. Afortunadament, es va desenvolupar i patentar una nova metodologia (WO2017105666A1) que no requeria l'ús de nanocàpsules de nucli i coberta. En canvi, les solucions fotocròmiques es nanoemulsionaven en solucions aquoses de polímers formadors de pel·lícula i després la nanoemulsió resultant es precipitava com a pel·lícules que conservaven la transparència i la ràpida velocitat de canvi de color de les solucions líquides. Com a resultat d'aquesta tesi, recentment també s'ha publicat un article científic que explica el funcionament i els avantatges d'aquesta tecnologia (Mater. Horiz., 2020,7, 2749). Gràcies a la interacció amb empreses potencialment interessades, es van identificar altres objectius clau a superar perquè la pel·lícula fotocromàtica es pogués utilitzar en productes comercials. Aquests objectius eren 1) millorar la coloració activada, 2) millorar l'estabilitat a la humitat, 3) reduir la terbolesa de les pel·lícules, 4) millorar la fatiga a l'exposició solar i 5) demostrar l'escalabilitat del procés de fabricació. Aquests objectius es van assolir entre el segon i el quart any de la tesi i els materials desenvolupats d'aquesta manera ara són adequats per a aplicacions industrials òpticament transparents. A més, la tècnica desenvolupada permet modificar les propietats fotocromàtiques i mecàniques de les pel·lícules per tal de complir els requisits específics de cada aplicació industrial. Mentrestant, es van produir prototips d'ulleres de sol, finestres intel·ligents i una visera de casc de motocicleta. També es van preparar prototips de vidres de construcció i parabrises amb maquetes d'un vehicle i un edifici. Aquests prototips es van utilitzar per comparar-los amb alguns productes fotocromàtics actualment disponibles al mercat, mostrant resultats prometedors i avantatges competitius per a productes basats en la captura de nanoemulsions. Aquests prototips són utilitzats actualment com a demostradors per Futurechromes SL per tal de contactar amb fabricants industrials i socis per promoure la comercialització de productes innovadors basats en la tecnologia de captura de nanoemulsions fotocromàtiques.

The main application of these materials is to incorporate them into products that require high transparency, but also rapid and real-time control of light transmission: The clearest example of this is prescription glasses, which can be clear and colorless inside buildings, but darken to provide comfort to the user once exposed to sunlight, thus avoiding having to carry a spare pair of sunglasses. In fact, photochromic ophthalmic glasses are currently the largest industrial application sector for photochromic dyes, with a global market of 4.8 billion dollars in 2018. In this sector we find products such as Transitions® lenses, with a change time of 3 to 5 minutes. With the nanoemulsion trapping technology developed in this thesis, Futurechromes wants to offer a superior response to eyeglass users and capture a significant part of this market. In the same vein, there are also sports and automotive applications, where the most important thing is to avoid glare caused by the sun and sudden changes in the weather, but it is also necessary to guarantee maximum visibility when entering or exiting tunnels or shaded areas. This market is smaller than that of ophthalmic glasses, as it is much more sensitive to the speed of color change, since the safety of the athlete or driver is at stake. Current sports products, such as Pinlock® ProtectTINT motorcycle helmet lenses, also have a change time of between 3 and 5 minutes. This response is too slow for many users and therefore, it is not a product in high demand. On the other hand, products that incorporate our nanoemulsion trapping technology react much faster, in just a few seconds. It is for this reason that we believe that the technology of this thesis could not only be well received in this sports market, but also boost it, generate more demand for this type of product and generate a positive impact on society, making the practice of sports and driving safer. Therefore, at Futurechromes we have prepared prototypes of these two products, incorporating our nanoemulsion trapping technology (Figure 2). With these prototypes at Futurechromes we have contacted companies from both the world of ophthalmics and sports equipment, as well as producers of raw materials. The reception by the companies contacted is good and we hope to sign specific technology licensing agreements in the coming months. The second area of ​​application for our technology is that of smart glass, which allows saving energy invested in air conditioning by reducing heat input through windows, but without reducing their visibility, and at the same time letting in as much light as possible on foggy and cold days to save on artificial light and heating. In this sector, the speed of change is not as relevant as in the previous ones, but fatigue resistance and price are of great importance. The smart window market is valued at 2.6 billion dollars (2018) and is currently dominated by electrochromic systems, such as Saint-Gobain's SageGlass®. These materials are expensive to produce and require specialized installation and electricity consumption. On the other hand, current photochromic options for smart windows, such as those offered by the company ColorVu, are much cheaper and easier to install, but have much less acceptance in the market due to their short useful life. At Futurechromes, we have discovered that the nanoemulsion trapping technique allows us to extend the life of photochromic dyes, since our matrix makes it difficult for oxygen (the main degrading agent of these dyes) to enter the material. In addition, tests carried out during the PhD showed that prototypes of smart windows prepared with our technology (Figure 3) had an energy saving efficiency similar to those obtained with commercial smart windows. Therefore, we hope to introduce our technology to the smart glass market, to obtain a product at an affordable price, save energy and reduce the environmental impact of buildings, and that also have good fatigue properties and resistance to the elements. We are currently in contact with a smart window production company and hope to carry out pilot production tests before 2021 in order to evaluate the commercial viability of these products.

Nanostructured Photochromic Materials; Photoprotective Coatings; Eyeglasses; User Comfort; Smart Glasses; Energy Saving; Photochromic Dyes; Liquid-Core Nanocapsules; Polymer Films; Commercial Products; Transparency; Aggregation; Novel Methodology; Patented Technology; WO2017105666A1; Core-Shell Nanocapsules; Photochromic Solutions; Nanoemulsification; Aqueous Solutions; Film-Forming Polymers; Nanoemulsion Precipitation; Films; Rapid Color Change Rate; Liquid Solutions; Scientific Article; Mater. Horiz., 2020,7, 2749; Activated Coloration; Humidity Stability; Turbidity Reduction; Solar Exposure Fatigue; Manufacturing Process Scalability; Optically Clear Industrial Applications; Photochromic Properties; Mechanical Properties; Industrial Application Requirements; Sunglasses Prototypes; Smart Windows Prototypes; Motorcycle Helmet Visor Prototypes; Construction Glass Prototypes; Windshields Prototypes; Mock-ups; Commercial Photochromic Products; Promising Results; Competitive Advantages; Nanoemulsion Trapping; Demonstrators; Futurechromes S.L.; Industrial Manufacturers; Partners; Commercialization; Innovative Products.