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One of the current issues in the development of devices based on porous thin films synthesized by sol gel is the eventual failure of the structural integrity of these systems due to chemical or mechanical stresses. In order to design and build robust systems, it is necessary to evaluate the role that each material forming the device has over its mechanical performance and chemical stability, considering their individual properties, their spatial arrangement, and the interfaces between them. In this work, the structural and mechanical evaluation of multilayers based on silica and titania mesoporous films is presented, and the variables that affect the structural integrity of these multilayered devices are evaluated. In addition, the chemical and mechanical stability of these optical devices against flow stress is assessed, simulating operating conditions of the sensors in a liquid environment. Single layer, bilayers, and multilayered devices were synthesized using the sol–gel method in combination with surfactant self-assembly, and their mechanical and structural properties were evaluated with electron and optical microscopy, X-ray reflectometry, and instrumented indentation. After these studies, improvements to the materials forming the device are proposed to maximize the structural integrity of the system. Highlights: Silica mesoporous films present a ductile behavior while titania mesoporous films are more brittle. The spatial disposition of SiO2 and TiO2 layers in bilayer structures modifies the failure mode. The mesoporous SiO2–TiO2 multilayer mechanical behavior is modulated by the SiO2 layers. The optical and mechanical behavior of the photonic device changes after immersion in water at 40 °C. [ABSTRACT FROM AUTHOR]

Ordered mesoporous oxides obtained by combining sol-gel and self-assembly exhibit high surface area, controlled porosity, monodisperse pores in the mesoscale and amorphous or crystalline inorganic framework. In the particular form of thin films, they have been widely studied for a diversity of applications. In this context, the mechanical stability of devices based on mesoporous thin films (MTF) is one of the critical factors to consider for assuring robustness and reliability. Measuring and understanding the mechanical and tribological behavior of these designed materials are therefore issues of crucial importance when large-scale applications are pursued, such as photovoltaic devices, catalysis, sensors, microfluidic systems, biocompatible films and microelectronics. In this review, two aspects are discussed and critically evaluated: the mechanical properties of ordered MTF and the experimental techniques used to measure them. The relationship between hardness and elastic modulus with structural features (porosity, pore ordering, crystalline phase, among others) are analyzed for several mesoporous systems. Tribological and fractomechanical features are also assessed. Besides, the experimental techniques dedicated to measure the mechanical properties of porous thin film, including surface acoustic waves, Brillouin light scattering, ellipsometric porosimetry, X-Rays and neutron-based techniques and nanoindentation are described in detail, discussing the possibilities and limitations of these techniques applied to a diversity of systems. Highlights: Several techniques can be used to evaluate the mechanical behavior of mesoporous thin films. Ordered mesoporous films are excellent systems to correlate structure and mechanical properties. For mesoporous films, elastic modulus and hardness values decrease as porosity increases. For titania films, the crystalline phase and the porosity determine their mechanical strength. Mechanical properties of hybrid films can be designed by changing the composition and porosity. [ABSTRACT FROM AUTHOR]