Limits imposed by liquid/surface interactions in the determination of tortuosity in mesopores

LINCK, LEONEL GARRO; MALDONADO OCHOA, SANTIAGO AGUSTÍN; CEOLÍN, MARCELO; CORTI, HORACIO; MONTI, GUSTAVO A.; CHÁVEZ, FABIAN VACA; ACOSTA, RODOLFO H.

MICROPOROUS AND MESOPOROUS MATERIALS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2020 vol. 305 p. 110351 - 110359

1387-1811

The restricted mobility of different liquids, polar and non-polar, were studied by means of 1H NMR diffusion andLarmor frequency dependent relaxation measurements, upon confinement in mesoporous silica with mean poresizes ranging from 3?30 nm. The use of alkanes as a reference in the determination of the true tortuosity valuewas observed to be accurate for pores larger than 6 nm, while for smaller pore sizes geometrical restrictionsaffect the diffusion even for short chain linear alkanes. 1H NMR fast field cycling relaxometry was used tomeasure the relaxation times as a function of the Larmor frequency. We observed that the total observabledispersion (TOD), which is a measure of the surface/liquid interaction, is mainly driven by the liquid polarity forpores larger than 10 nm, while less dependence on polarity is observed for smaller pore sizes. Our results indicatethat as confinement increases, liquid/surface interactions become more relevant than the structural properties ofthe porous network, imposing a limit to the use of alkanes to probe the geometrical tortuosity.