Ionic liquids (ILs) show promise as lubricants for nano- and microelectromechanical systems (NEMS/MEMS) and hard disc drives (HDDs). When deposited on solid substrates as nanometer-thick films, these liquids can exhibit a solid-like layering structure, which makes them ideal as lubricants. Moreover, ILs are “designer” materials with many possible molecular structures and tunable properties. In this work, we have experimentally investigated the friction of various nanometer-thick fluorinated ILs on a silica surface using a nanotribometer. We found that surface tension has a significant effect on the friction. When the surface tension of ILs is low, ILs wet the silica surface, and the friction is low. However, when the surface tension is high, ILs form droplets and do not wet the silica surface, which results in higher friction. The effect of moisture at the interface has also been investigated, and the results suggested that water promotes the surface charging of silica, which induces more ordered cation/anion layering and thus reduces the friction. The finding here is critical in designing novel nanometer-thick IL lubricants.
Maleic anhydride is an important raw material in many chemical reactions, and very often, condensation is required to reflux maleic anhydride back to the reactor. It has been shown that severe fouling occurs to the maleic anhydride condenser, which is a major challenge to the operation in chemical plants. Clearly, an efficient mitigation plan is highly dependent on the understanding of the underlying mechanisms. However, the mechanisms of the fouling in the maleic anhydride condenser remain unclear to date. Here we report our experimental efforts in (1) uncovering the governing mechanisms of the fouling in maleic anhydride condensers and (2) developing the strategy to combat the condenser fouling. Our in-situ interface characterization and 1H NMR results suggest that the condensed maleic anhydride, which is a liquid, is pinned on the condenser surface and thus reacts with the trace amounts of water to produce maleic acid, which is a solid. The maleic acid solid particles accumulate on the condenser surface and over a short period of time, i.e., days to weeks, will plug the condenser tubes. The key enabler of this process is that the maleic anhydride droplets are pinned on the tube surface and do not roll off the surface, which results from the high roughness of the condenser surface. We found that, after the surface roughness is reduced by machining, the maleic anhydride droplets roll off the tube surface much more easily, indicating this is a promising approach to reduce the condenser fouling.
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