Cryoporometry in Femtoliter Volumes by Confocal Raman Spectroscopy

Abstract

The properties of porous material are largely dependent on the size, shape, and connectivity of the pores. Here, we present a method based on confocal Raman spectroscopy to quantify porosity using a cryoporometric approach. We show that the phase transition of water imbibed in porous silica can be accurately determined using two different, but complementary methodologies. The first one relies on integrating the temperature-dependent spectral intensities across the whole OH (H 2 O) or OD (D 2 O) stretching region. The second, more quantitative approach, deconvolutes the spectral contributions within the pores in terms of liquid and solid fractions. The results show the expected reciprocal dependence of the average phase transition point with pore size, as well as the typical hysteresis between the freezing and melting transitions. One of the key advantages of the confocal Raman approach is its high spatial resolution, with sampling volumes starting from just a few femtoliters, opening the possibility of mapping the structure in heterogeneous porous materials.

Advanced NMR Cryoporometry

“…On the one hand, there is an instrumental aspect. Among different options of preforming thermoporometry, such as differential scanning calorimetry [31], X-ray [44,45] and neutron [46,47] scattering, Raman spectroscopy [48,49], sound [50] and light [51], NMR cryoporometry is proven to be a very powerful approach allowing for an easy discrimination between solid and liquid phases based on different mobilities of the molecules in the two phases [52][53][54]. Moreover, it can be combined with other NMR experiments (relaxometry, diffusometry, MAS solid-state NMR) so that more information can be gained about the system under study [8,40,[55][56][57][58][59][60][61][62][63][64][65][66].…”