Particulate vs monolithic aerogel linings in capillaries for Raman signal gain of aqueous solutions

We compare particulate versus monolithic silica aerogel-lined capillaries as liquid core waveguides for Raman signal gain of liquid aqueous samples. The manufacturing process of monolithic linings, which aims to address the limited robustness of particulate aerogel linings, is discussed in detail and compared with that of particulate linings. The linings of both capillary types are characterized using scanning electron microscopy. Raman signal gain of pure water and aqueous solutions is evaluated for each type. The aqueous solutions are samples drawn at different times from the oxidative conversion of glycerol to formic acid (OxFA process). It is analyzed whether the Raman signal gain provided by aerogel-lined capillaries is affected by the property changes in this exemplary industrial process caused by the ongoing chemical reaction. Finally, the mechanical robustness of the linings and the stability of the Raman signal gain are tested under rapid and repeated capillary purge in both types.