The self-assembly of linear model surfactants into reverse micelles (RMs) in a nonpolar solvent is studied here for two surfactant lengths, through numerical simulations. The study was carried out at...

Liquid and surface polarities play an important role in wetting phenomena, and this should still be true if the surface is rough. We analyze the wetting of high-polar and low-polar liquids on rough low-polar surfaces made of polystyrene. The experimental results are analyzed by the surface tension components (STC) and the equation-of-state (EQS) approaches. Both approaches predicted a clear increase of the contact angle (CA) with the surface roughness for high-polar liquids, but they failed for lowpolar liquids: STC calculations produce the wrong tendency in the total solid surface energy, and EQS is not able to fit the data for these liquids. These results show that low-polar liquids show little dependence on the roughness of a low-polar surface, while high-polar liquids are very sensitive to it. As a consequence, the calculated CAs are close to experimental values only for the high-polar liquids, while there are great differences for low-polarity liquids. Both STC and EQS approaches are able to describe the apparent CAs on polystyrene rough surfaces by using effective surface and interfacial tensions, but their effectiveness is limited to high-polarity liquids.

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Two of the most commonly encountered friction reducing agents used in plastic sheet production are the amides known as erucamide and behenamide, which despite being almost identical chemically, lead to markedly different values of the friction coefficient. To understand the origin of this contrasting behavior, in this work we model brushes made of these two types of linear -chain molecules using quantum mechanical numerical simulations under the Density Functional Theory at the B97D/6-31G(d,p) level of theory. Four chains of erucamide and behenamide were linked to a 2X10 zigzag graphene sheet and optimized both in vacuum and in continuous solvent using the SMD implicit solvation model. We find that erucamide chains tend to remain closer together through π -π stacking interactions arising from the double bonds located at C13-C14, a feature behenamide lacks and thus a more spread configuration is obtained with the latter. It is argued that this arrangement of the erucamide chains is responsible for the lower friction coefficient of erucamide brushes, compared with behenamide brushes, which is a macroscopic consequence of cooperative quantum mechanical interactions. While only quantum level interactions are modeled here, we show that behenamide chains are more spread out in the brush than erucamide chains as a consequence of those interactions. The spread out configuration allows more solvent particles to penetrate the brush, leading in turn to more friction, in agreement with macroscopic measurements and mesoscale simulations of the friction coefficient reported in the literature.

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