title: Ab Initio Modeling Of Friction Reducing Agents Shows Quantum Mechanical Interactions Can Have Macroscopic Manifestation.
abstract: 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 2 × 10 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.
authors: Centro de Investigación en Ciencias Físico-Matemáticas, Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León , San Nicolás de los Garza 66450, Nuevo León, Mexico.
authors: J D
authors: JD
authors: Hernández Velázquez
authors: Centro Conjunto de Investigación en Química Sustentable, UAEM-UNAM , Carretera Toluca-Atlacomulco Km 14.5, Unidad San Cayetano-Toluca 50200, Estado de México, Mexico.
authors: J
authors: J
authors: Barroso-Flores
authors: División de Ingeniería Química y Bioquímica, Tecnológico de Estudios Superiores de Ecatepec , Av. Tecnológico s/n, Ecatepec 55210, Estado de México, Mexico.
authors: A
authors: A
authors: Gama Goicochea