Polymer on Top: Current Limits and Future Perspectives of Quantitatively Evaluating Surface Grafting

Abstract

Well-defined polymer strands covalently tethered onto solid substrates determine the properties of the resulting functional interface. Herein, the current approaches to determine quantitative grafting densities are assessed. Based on a brief introduction into the key theories describing polymer brush regimes, a user's guide is provided to estimating maximum chain coverage and—importantly—examine the most frequently employed approaches for determining grafting densities, i.e., dry thickness measurements, gravimetric assessment, and swelling experiments. An estimation of the reliability of these determination methods is provided via carefully evaluating their assumptions and assessing the stability of the underpinning equations. A practical access guide for comparatively and quantitatively evaluating the reliability of a given approach is thus provided, enabling the field to critically judge experimentally determined grafting densities and to avoid the reporting of grafting densities that fall outside the physically realistic parameter space. The assessment is concluded with a perspective on the development of advanced approaches for determination of grafting density, in particular, on single-chain methodologies.

The performance of functional polymer interfaces is not only determined by the type of tethered macromolecule, but critically rests on the density of the grafted chains. The key characteristics of the current methods for grafting-density determination are quantitatively assed, while, concomitantly, a perspective is provided for the development of advanced and direct methods to assess this critical parameter.

http://ift.tt/2oRG7OX