Ab Initio Modeling Of Friction Reducing Agents Shows Quantum Mechanical Interactions Can Have Macroscopic Manifestation

摘要

Two of the most commonly encountered friction reducing agents used in plasticsheet production are the amides known as erucamide and behenamide, whichdespite being almost identical chemically, lead to markedly different values ofthe friction coefficient. To understand the origin of this contrastingbehavior, in this work we model brushes made of these two types of linear chainmolecules using quantum mechanical numerical simulations under the DensityFunctional Theory at the B97D/6-31G(d,p)level of theory. Four chains oferucamide and behenamide were linked to a 2X10 zigzag graphene sheet andoptimized both in vacuum and in continuous solvent using the SMD implicitsolvation model. We find that erucamide chains tend to remain closer togetherthrough {\pi}{\pi} stacking interactions arising from the double bonds locatedat C13 C14, a feature behenamide lacks and thus a more spread configuration isobtained with the latter. It is argued that this arrangement of the erucamidechains is responsible for the lower friction coefficient of erucamide brushes,compared with behenamide brushes, which is a macroscopic consequence ofcooperative quantum mechanical interactions. While only quantum levelinteractions are modeled here, we show that behenamide chains are more spreadout in the brush than erucamide chains as a consequence of those interactions.The spread out configuration allows more solvent particles to penetrate thebrush, leading in turn to more friction, in agreement with macroscopicmeasurements and mesoscale simulations of the friction coefficient reported inthe literature.