Adsorption of Dendritic Fluorocarbon End-Capped Poly(Ethylene Oxide) at an Air-Water Interface – A Synthetic, Analytical and Computational Study

Abstract

Adsorption of amphiphilic polymer molecules to an interface can induce interesting properties on both the bulk of the material as well as the interface itself. Previous experiments carried out by other groups at Durham University have shown that functionalizing PEO with fluorocarbon groups can lead to a remarkably large increase in adsorption and evidence has been provided for the formation of brush-like structures at an air/water interface. However the maximum size of the fluorocarbon unit is limited by its solubility in organic solvents.

In order to try and overcome this problem a new synthetic strategy has been employed wherein the PEO chain is functionalized using a dendrimer, enabling multiple functional groups to be attached to a single polymer chain. Conformational and concentration dependence information can be found using neutron reflectometry.

A key component of this project is to utilize molecular dynamics (MD) to simulate the behaviour of these polymers at liquid surfaces. For relatively short polymer chains, it is possible to quantitatively model the distribution function for chains at a water-air interface by employing atomistic simulation techniques, allowing for direct predictions of the neutron reflectivity data. For long chains atomistic representations of the polymer and water are no longer feasible but we model the poly(ethylene oxide) using coarse-grained models. The advantage of coarse-graining (CG) is that it allows us to simulate much longer chains and much higher surface concentrations allowing direct predictions for the neutron reflectivity based on the calculated distribution functions for the CG-polymer at each surface concentration.

By direct comparison of experimental and computational data we will substantially increase our understanding of the behaviour of amphiphilic polymer molecules at interfaces. This study will also enable us to synthesize materials with very high surface adsorption.