Adsorption and viscosity measurement of interfacial and nanoconfined water using surface and shear acoustic wave techniques

Water is a well studied substance. Also, its abundance or scarcity has driven the evolution of biomaterials and pathways. Some of the basic properties of water, its viscosity when restricted to only a few molecular layers being an example, are topics of much debate within the scientific community. Conventional methods for measuring this elusive property involve using shear force microscopy, atomic force microscopy, or a surface force balance. These techniques require the use of a probe that is brought within close proximity to a particular substrate. The results from such investigations have been as diversified as water is omnipresent. This body of work presents simultaneous adsorption and viscosity measurement of water restricted to only a few molecular layers in thickness using acoustic wave techniques. Also, it is this author's opinion that the presence of probes is a reason for the observation of such anomalous viscosity data. In this study, an experimental approach is developed with the necessary sensitivity to measure the viscosity and adsorption of molecular layers of water, but also it will be shown that no evidence is observed leading to the conclusion that interfacial and nanoconfined water has viscosities that are orders of magnitude greater than that of bulk water.;Surface coverage of the water studied was controlled using similar techniques designed for humidity sensor calibration. This control of surface occupancy is a necessity in the measurement of a fluid layer's viscosity restricted to only a few molecules in thickness. Previous attempts to study so precisely the adsorption of water on an ideal surface have been conducted with simulation. In this work, experimental data for the adsorption of water is presented and compared to the data resulting from simulated isotherms.;For both the adsorption and viscosity measurements, three chemically different single-crystal ST-x quartz surfaces are studied, in order to explore the effect of nanoconfinement on the viscosity of water, nanometer sized pores in a cubic mesoporous silica material were filled with the fluid of interest by exposing a thin film of the porous material to the necessary partial pressure required for capillary condensation according to the Kelvin equation. Water adsoption data for this material also was obtained. For the confined case, the viscosity measured did not exceed that of the bulk case. It was evident that a nanoporous film having a thickness of 100nm was required for the measurement system to detect a bulk viscosity value while preserving the condition of nanoconfinement. In addition to these data, water adsorption isotherms for a patternable superhydrophobic aerogel material are presented. Such data from novel nanomaterials that do not have bulk analogues is of great industrial importance and has been made available for the first time in this presented work.