Materiales fotocrómicos de respuesta rápida mediante atrapamientos de nanoemulsiones

Héctor Torres Pierna

Claudio Roscini

El objetivo de esta tesis fue explorar el potencial de los materiales fotocrómicos nanoestructurados como recubrimientos fotoprotectores para gafas, con el fin de proporcionar comodidad al usuario, y para gafas inteligentes que ahorran energía. Inicialmente, los colorantes fotocrómicos se disolvieron dentro de las nanocápsulas de núcleo líquido. Posteriormente, las cápsulas se dispersaron en películas de polímero que podrían integrarse en productos comerciales. Sin embargo, mantener la transparencia adecuada al integrar las cápsulas resultó ser muy difícil, incluso cuando las cápsulas estaban a escala nanométrica, debido a la agregación. Afortunadamente, se desarrolló y patentó una nueva metodología (WO2017105666A1) que no requería el uso de nanocápsulas de núcleo-cubierta. En su lugar, las soluciones fotocrómicas se nanoemulsionaron en soluciones acuosas de polímeros formadores de película y luego la nanoemulsión resultante se precipitó en películas que conservaron la transparencia y la rápida tasa de cambio de color de las soluciones líquidas. Como resultado de esta tesis, recientemente se publicó un artículo científico que explica el funcionamiento y las ventajas de esta tecnología (Mater. Horiz., 2020, 7, 2749). Gracias a la interacción con empresas potencialmente interesadas, se identificaron otros objetivos clave para que la película fotocrómica pudiera utilizarse en productos comerciales. Estos objetivos eran: 1) mejorar la coloración activada, 2) mejorar la estabilidad a la humedad, 3) reducir la turbidez de las películas, 4) mejorar la fatiga a la exposición solar y 5) demostrar la escalabilidad del proceso de fabricación. Estos objetivos se alcanzaron entre el segundo y el cuarto año de la tesis, y los materiales desarrollados de esta manera ahora son adecuados para aplicaciones industriales ópticamente transparentes. Además, la técnica desarrollada permite modificar las propiedades fotocrómicas y mecánicas de las películas para cumplir con los requisitos específicos de cada aplicación industrial. Mientras tanto, se produjeron prototipos de gafas de sol, ventanas inteligentes y una visera para casco de motocicleta. También se prepararon prototipos de vidrio para construcción y parabrisas con maquetas de un vehículo y un edificio. Estos prototipos se utilizaron para compararlos con algunos productos fotocrómicos disponibles actualmente en el mercado, mostrando resultados prometedores y ventajas competitivas para los productos basados en la captura de nanoemulsiones. Futurechromes SL utiliza estos prototipos como demostradores para contactar con fabricantes y socios industriales y promover la comercialización de productos innovadores basados en la tecnología de captura de nanoemulsiones fotocrómicas.

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.