Materiais e dispositivos fotônicos: de nanopartículas a sensores químicos de fibra óptica

Author(s)

Marco César Prado Soares

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2024-02-23

Examining board members

Eric Fujiwara; Cecília Amélia de Carvalho Zavaglia; Julio Roberto Bartoli; Patricio Salvatore La Rosa; Thiago Destri Cabral

• Advisor: Eric Fujiwara

Abstract

Nowadays, several techniques and materials are available for the fabrication of optical fibers, waveguides and optic sensors, but technological gaps remain. Sensors with lower costs and minor difficulties of fabrication, signal processing, and feasibility; or obtained through less-aggressive methodologies as biodegradable or greener devices are demanded. In the case of chemical and biochemical process monitoring, characteristics inherent to optical fibers such as environmental and electromagnetic resistances are also desirable, once harsh thermal, chemical and mechanical conditions are usually present. This work proposes, then, the design and fabrication of photonic materials and devices where nanotechnology and fiber optic technology are explored to obtain more sustainable processes and devices with interesting characteristics for inline operation. New fluorescent nanomaterials from the class of carbon nanodots (CDs, particles with diameters in the order of 10 nm or less) were synthesized from three natural sources (sugarcane syrup, orange juice, and UHT milk), and the sugarcane-based particles were occluded into a hydrogel matrix (gelatin) for being introduced into a microstructured polymer optical fiber. So, a waveguide capable of emitting and conducting visible light was fabricated as a greener alternative to the incorporation of rare-earths and heavy metals on luminescent fibers manufacturing. Another hydrogel with better mechanical properties (agarose) was doped with SiO2-CDs nanocomposites for obtaining a fluorescent, biodegradable and biocompatible pH sensor useful for retrieving information for offline analysis. Moreover, it was verified that CDs-PMMA nanocomposites can be combined with solar cells. An increase of 11.3% on the cell conversion efficiency was observed, revealing great potential for applications in optoelectronics and renewable energies. Fiber optic sensors were also designed and applied to important chemical and biochemical media. A sensing system capable of detecting velocity and refractive index (RI) in biphasic gas-water, oil-water and gas-oil mixtures was 3D-printed as a millifluidic device with an inserted tilted fiber Bragg grating, showing important applications on petrochemistry. A smartphone-based RI sensor was then designed for the real-time assessment of fed-batch fermentors. The project attends some "Industry 4.0" requirements: the sensor is destined to field monitoring and on-site fast fabrication, relying on a simple 3D-printed case for coupling optical fibers to the phone’s camera and LED. Then, an application is responsible for processing light intensity data and correlating signal variations to the broth RI, which is function of the sucrose concentration according to Fresnel law. Finally, a dynamic light scattering sensor based on an all-optic Fresnel reflectance setup applies artificial neural networks for detecting concentration disturbances and performing the simultaneous assessment of concentration and flow speed of nanofluids. These nanofluids, were obtained by synthesizing SiO2 nanoparticles (diameter of 195 nm) and dispersing them in water. From traditional chemical, petrochemical, and mining to food and advanced biotechnology, several industries must deal with nanofluids and colloidal suspensions, so there is a range of important practical applications of this sensor on facilities control and monitoring (AU)

• FAPESP's process: 19/22554-4 - Design and fabrication of non-conventional optical fibers for chemical sensing
• Grantee: Marco César Prado Soares
• Support Opportunities: Scholarships in Brazil - Doctorate