(257c) Liquid/Solid Interaction-Dependent Nanofriction Coefficient at Simple Fluid/Solid Interfaces

The aquaporin channel fulfills the dual and seemingly conflicting requirements of transporting water selectively while optimizing permeability. This raises questions concerning the nature of the interfacial nanofluidic transport, in particular the role of the liquid-solid interaction and its effect on the nanofriction coefficient at the fluid-solid interface. As an application of the experimental information and the theoretical background needed to analyze the experiments, we chose three simple, nonpolar, quasi-spherical liquids-cyclohexane (C₆H₁₂), carbon tetrachloride (CCl₄) and octamethylcyclotetrasiloxane (OMCTS)-to focus fundamental surface force studies on three planar substrates - graphite, silica and mica. The fluid/solid interfacial nanofriction coefficient measured by Atomic Force Microscopy (AFM) is observed to depend on the surface wetting parameter α_w(a relative value, described as the ratio^1-3 of liquid/solid interaction divided by liquid/liquid interaction). The different sensitivities of the plot for friction coefficient vs α_w on graphite, silica and mica surfaces require consideration of the dependence of the nanofriction coefficient on the liquid/solid interaction. This enables us to explore in a systematic way the role of the strength of the liquid/solid interactions on the nanofriction coefficient. By comparing the dynamic behavior of liquids C₆H₁₂, CCl₄on the three planar surfaces, we were able to demonstrate that small changes of liquid/solid interactions deeply influence the nanofriction coefficient at the fluid/solid interface. More surprisingly, we have found that the natural logarithm of the nanofriction coefficient at the fluid/solid interface is linearly dependent on the natural logarithm of the liquid/solid interactions. It is noteworthy that the OMCTS/substrate interactions could be obtained by this linear model from the measured nanofriction coefficients, and the interactions are in excellent agreement with those calculated by simulation. The linearly quantitative model is expected to provide a general tool to investigate liquid/solid interactions according to AFM-measured nanofriction coefficients, and to open up a perspective in designing functional surfaces.

 

References

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            (3)        Gubbins, K. E.; Long, Y.; Sliwinska-Bartkowiak, M. The Journal of Chemical Thermodynamics 2014, DOI: 10.1016/j.jct.2014.01.024.