The effect of chain architecture and brush topology on the tribology of polymer brushes using coarse-grained molecular dynamics
File(s)
Author(s)
Abdelbar, Mohamed
Type
Thesis
Abstract
This thesis investigates the tribology of polymer brush bilayers (PBBs) in good solvents under stead-state shear, employing coarse-grained (CG) non-equilibrium molecular dynamics (NEMD) simulations to explore the impact of chain architecture, chain length, grafting density, state of compression and sliding velocity on their frictional behavior. Setting the stage for our simulations, we review the evolution of CG MD models for polymer brushes (PBs) and outline recently developed theoretical scaling laws for PBBs, which are found, in general, to be in good agreement with our simulation results. Additionally, our findings reveal that the architecture of the grafted chains—specifically, cyclic and loop configurations—significantly reduces friction and interpenetration under shear stress compared to traditional linear chain architectures. We compare our simulation results with tribological data and find qualitatively similar trends as a function of the various parameters under investigation. Although the friction evaluated through our NEMD simulations is usually lower than measured experimentally, this is to be expected due to the additional dissipation channels active for real systems compared to our idealized setup. This underscores the necessity for ongoing refinement of simulation models, demonstrates the predictive capacity of molecular simulation techniques and promotes their use for extracting design principles for lubricious polymer brushes with tunable friction properties.
Version
Open Access
Date Issued
2024-03-12
Date Awarded
01/08/2024
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Angioletti-Uberti, Stefano
Dini, Daniele
Ewen, James
Sponsor
Engineering and Physical Sciences Research Council
Grant Number
(EP/G036888/1)
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)