Between Industrial Partnerships and Basic Research: An Example from My Work on Glassy Silica

By Pascal Etienne, Charles Coulomb Laboratory (L2C).

Vitrous silica is valued for its high purity, transparency, and very low thermal expansion. It is refractory, resistant to thermal shock, and resistant to many chemical agents, making it a material of choice for optics, for applications involving high temperature gradients, and for applications requiring chemical inertness. Its ultra-porous form (aerogel), achieved through sol-gel synthesis and drying under supercritical conditions, gives it exceptional thermal insulation properties as well as a very low refractive index, close to that of air. However, silica has a major drawback that can limit its use: its brittle behavior and the subcritical propagation of its defects under stress, which can lead to delayed catastrophic failure.

My presentation focuses on research conducted in response to requests from industry representatives interested in using silica to manufacture sensors. The idea is to highlight another—and certainly less well-known—aspect of my expertise, which is centered not on hybrid materials but on glasses.

The first section focuses on a collaboration initiated by SAFRAN Electronics & Defense. This company is a leader in the manufacture of gyroscopes incorporating silica resonators for inertial navigation. Here, the key characteristic of interest is the high quality factor resulting from low internal friction. This factor is closely dependent on the size of internal defects, such as microcracks. The manufacturing process uses commercial silica that is machined and then etched to remove any surface defects. But what about internal defects? Can they propagate over time, potentially leading to a decline in the gyroscope’s performance?

The second part is the result of a collaboration with the French pharmaceutical company Medincell, which specializes in technologies for the subcutaneous administration of drugs. The rapid development of these products requires high-throughput screening using UV spectrophotometry on very small quantities. The best solution is to develop an optofluidic device based on total internal reflection to maximize the optical path length. The very low refractive index of silica aerogels makes them an excellent candidate. But how can a channel with very low propagation losses be fabricated within the aerogel? Is it possible to prevent liquid from entering its pores? Won’t its extreme fragility make it impossible to use?

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