Optical porosimetry of weakly absorbing porous materials

International audienceThe physical porosity Φ of a porous material determines most of its properties. Although the optical porosity Φ opt can be measured, relating this quantity to Φ remains a challenge. Here we derive relationships between the optical porosity, the effective refractive index n eff and the physical porosity of weakly absorbing porous media. It introduces the absorption enhancement parameter B, which quantifies the asymmetry of photon path lengths between the solid material and the pores and can be derived from the absorption coefficient µ a of the material. Hence Φ can be derived from combined measurements of n eff and µ a. The theory is validated against laboratory measurements and numerical experiments, thus solving a long-standing issue in optical porosimetry. This suggests that optical measurements can be used to estimate physical porosity with an accuracy better than 10%

Optical porosimetry of weakly absorbing porous materials

International audienceThe physical porosity Φ of a porous material determines most of its properties. Although the optical porosity Φ opt can be measured, relating this quantity to Φ remains a challenge. Here we derive relationships between the optical porosity, the effective refractive index n eff and the physical porosity of weakly absorbing porous media. It introduces the absorption enhancement parameter B, which quantifies the asymmetry of photon path lengths between the solid material and the pores and can be derived from the absorption coefficient µ a of the material. Hence Φ can be derived from combined measurements of n eff and µ a. The theory is validated against laboratory measurements and numerical experiments, thus solving a long-standing issue in optical porosimetry. This suggests that optical measurements can be used to estimate physical porosity with an accuracy better than 10%