Bulk conformation and shear-induced transitions in bottlebrush poly(alkyl methacrylate): The role of side chain length and polymer flexibility

Abstract

Optimal design of polymeric friction modifiers (PFMs) in lubricating oils is crucial for enhancing energy efficiency. This study examines the impact of side chain length on the flexibility and conformation of bottlebrush PFM poly(alkyl methacrylate) in bulk oil solutions and under shear using molecular dynamics simulations. We semi-quantify polymer flexibility through cluster analysis, revealing coil-globule transitions at varying temperatures. Under shear, polymers exhibit translational and rotational motion with conformational changes, driven by shearing and temporary surface adsorption. A concentrated distribution of adsorbed atoms is crucial for stable adsorption in the subsequent translational phase. Polymers with shorter side chains demonstrate stable adsorption with a coil conformation, while those with longer side chains lack stable adsorption, repeating translation-rotation cycles and coil-globule transitions.