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Advancements in hybrid sol-gel technology have provided a new class of holographic materials as photopolymerizable glasses. Recently, a number of photosensitive glass compositions with high dynamic range and high spatial resolution have been reported and their excellent capability for volume holography has been demonstrated. Nevertheless, challenges remain, particularly in relation to the processing time and environmental stability of these materials, that strongly affect the performance and durability of the fabricated holograms. State-of-the-art photopolymerizable glasses possess long curing times (few days) required to achieve thick films, thus limiting the industrial implementation of this technology and its commercial viability. This article presents a novel, fast curing, water-resistant, photopolymerizable hybrid sol-gel (PHSG) for holographic applications. Due to introducing an amine-based modifier that increases the condensation ability of the sol-gel network, this PHSG overcomes the problem of long curing time and can readily produce thick (up to a few hundred micrometers) layers without cracking and breaking. In addition, this PHSG exhibits excellent water-resistance, providing stable performance of holographic gratings for up to 400 h of immersion in water. This finding moves photopolymerizable glasses to the next development stage and renders the technology attractive for the mass production of holographic optical elements and their use across a wide number of outdoor applications.

This paper investigates the role of the acid catalyst on the structure and anticorrosion barrier performances of a dual hybrid sol-gel coating composed 3-trimethoxysilylpropylmethacrylate and a zirconium complex and deposited on AA2024-T3 alloy. Along with the variation of the acid catalyst in the range 0.3 to 2, the zirconium complex concentration in the silicate matrix is altered from 10 to 30%. Mol. The structure of the materials is characterised using dynamic light scattering, Fourier-transform infrared spectroscopy, and 29Silicon nuclear magnetic resonance spectroscopy, while the thermal behaviour is identified by differential scanning calorimetry and the coating morphology analysed using scanning electron microscopy/energy dispersive x-ray spectroscopy. The anticorrosion barrier properties are characterised by electrochemical impedance spectroscopy and neutral salt spray. It is shown that the acid catalyst concentration has a direct impact on the kinetics of the hydrolysis and condensation reactions and that those effects can be controlled by the content of zirconium. These individual or combined alterations are found to directly impact the formation of Si-O-Zr bonds, thus the interconnectivity between the silicate matrix and the zirconium complex modifier, resulting in hybrid structures with altered densities. For the materials composed of 10 and 20 % of zirconium complex and when the pH is lowered, the relative concentrations of siloxane bonds is increased at the expenses of the Si-O-Zr bonds. When the concentration of zirconium complex is increased to 30 % and as the pH is increased, a higher competition in the formation of Si-O-Zr bonds takes place and are preferentially formed over the higher condensed Si-O-Si bonds. The corrosion testing show that the coatings with the highest barrier properties are found when the interconnectivity between the silicate and zirconium complex is maximum, thus for the materials exhibiting the highest condensation degrees.

This article reports on a fiber-based ratiometric optical pH sensor for use in real-time and continuous in vivo pH monitoring in human tissue. Stable hybrid sol-gel-based pH sensing material is deposited on a highly flexible plastic optical fiber tip and integrated with excitation and detection electronics. The sensor is extensively tested in a laboratory environment before it is applied in vivo in a human model. The pH sensor performance in the laboratory environment outperforms the state-of-the-art reported in the current literature. It exhibits the highest sensitivity in the physiological pH range, resolution of 0.0013 pH units, excellent sensor to sensor reproducibility, long-term stability, short response time of