Strain in material as sensor for chemistry

We present an in situ infrared reflection absorption spectroscopy (IRRAS) study of calcium silicate hydrate (C– S–H) phases formed on silicon wafers subjected to controlled tensile strain. By combining mechanical bending with spectroscopic measurements, we observe distinct strain-dependent shifts in the vibrational modes associated with the asymmetric stretching of Si–O–Si and Si–O–Ca linkages. A significant blue-shift from 1030cm⁻¹ to 1260cm⁻¹ indicates an angular tightening of the silicate network, while a weaker and symmetric red-shift from 1000 to 950cm⁻¹ is attributed to local bond elongation in terminal or less crosslinked units. The vibrational response is interpreted using a simplified cosine-based model, which relates bond angle changes to frequency shifts. Reference values from the tobermorite 11 Å structure provide a geometric baseline to estimate angle variations on the order of 1.5–2.0°. The results underscore the sensitivity of surface silicate structures to mechanical deformation and demonstrate the ability of IRRAS to detect subtle changes in bonding environments. We further discuss the limitations of the empirical model and the possible influence of interlayer water and metal coordination on the observed spectroscopic response.