AUTHOR=Ok Salim , Hwang Bohyun , Liu Tingting , Welch Susan , Sheets Julia M. , Cole David R. , Liu Kao-Hsiang , Mou Chung-Yuan 

TITLE=Fluid Behavior in Nanoporous Silica

JOURNAL=Frontiers in Chemistry

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.00734

DOI=10.3389/fchem.2020.00734

ISSN=2296-2646

ABSTRACT=<p>We investigate dynamics of water (H<sub>2</sub>O) and methanol (CH<sub>3</sub>OH and CH<sub>3</sub>OD) inside mesoporous silica materials with pore diameters of 4.0, 2.5, and 1.5 nm using low-field (LF) nuclear magnetic resonance (NMR) relaxometry. Experiments were conducted to test the effects of pore size, pore volume, type of fluid, fluid/solid ratio, and temperature on fluid dynamics. Longitudinal relaxation times (T<sub>1</sub>) and transverse relaxation times (T<sub>2</sub>) were obtained for the above systems. We observe an increasing deviation in confined fluid behavior compared to that of bulk fluid with decreasing fluid-to-solid ratio. Our results show that the surface area-to-volume ratio is a critical parameter compared to pore diameter in the relaxation dynamics of confined water. An increase in temperature for the range between 25 and 50°C studied did not influence T<sub>2</sub> times of confined water significantly. However, when the temperature was increased, T<sub>1</sub> times of water confined in both silica-2.5 nm and silica-1.5 nm increased, while those of water in silica-4.0 nm did not change. Reductions in both T<sub>1</sub> and T<sub>2</sub> values as a function of fluid-to-solid ratio were independent of confined fluid species studied here. The parameter T<sub>1</sub>/T<sub>2</sub> indicates that H<sub>2</sub>O interacts more strongly with the pore walls of silica-4.0 nm than CH<sub>3</sub>OH and CH<sub>3</sub>OD.</p>