Investigation of Roughness Correlation in Polymer Brushes via X-ray Scattering.

Marcus Hildebrandt,Sedakat Altinpinar,Wael Ali,Eui-Young Shin,Jochen S Gutmann,Suan Yang

doi:10.3390/polym12092101

Marcus Hildebrandt, Sedakat Altinpinar + Show 4 more

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https://doi.org/10.3390/polym12092101

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Abstract

Thin polymer films and coatings are used to tailor the properties of surfaces in various applications such as protection against corrosion, biochemical functionalities or electronic resistors. Polymer brushes are a certain kind of thin polymer films, where polymer chains are covalently grafted to a substrate and straighten up to form a brush structure. Here we report on differences and similarities between polymer brushes and spin-coated polymer films from polystyrene and polymethyl methacrylate with special emphasis on surface roughness and roughness correlation. The phenomenon of roughness correlation or conformality describes the replication of the roughness profile from the substrate surface to the polymer surface. It is of high interest for polymer physics of brush layers as well as applications, in which a homogeneous polymer layer thickness is required. We demonstrate that spin-coated films as well as polymer brushes show roughness correlation, but in contrast to spin-coated films, the correlation in brushes is stable to solvent vapor annealing. Roughness correlation is therefore an intrinsic property of polymer brushes.

Highlights

Thin polymer films are of high interest in various applications and disciplines, such as electronics, biomedicals or functional coatings [1,2]
In contrast to spin-coated films, the roughness correlation present in polymer brushes is stable to annealing at high temperatures, which was shown by unpublished results from
We concentrate on the similarities and differences in topography, surface roughness and roughness correlation between spin-coated films and polymer brushes and their behavior with respect to annealing

Summary

Introduction

Thin polymer films are of high interest in various applications and disciplines, such as electronics, biomedicals or functional coatings [1,2]. As no surface is ideally flat, height deviations appear, giving the surface a certain structure and roughness profile These deviations are described with the Root Mean Square (RMS) roughness, which averages the height deviation from a mean level along a sampling length. If thin polymer films are coated on a substrate, two roughness profiles exist, namely the silicon-polymer-interface and the top polymer surface. X-rays penetrate the polymer layer and XRR characterizes underlying interfaces, such as the film-substrate-interface [4,5]. Roughness studies of those systems have extensively been performed and reported in literature with the mentioned methods [3,6]. For example in conformal films, the roughness profile from one interface is copied to the overlaying surface, resulting in correlated roughness profiles and a constant layer thickness of the polymer film (Figure 1) [7,8]

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