Surface-grafted polymer gradients: Formation, characterization, and applications

This review presents to-date progress in the formation of surface-tethered polymer assemblies with gradually varying physico-chemical properties. The typical characteristics of the grafted polymers that may change spatially along the specimen include molecular weight, grafting density on the substrate, and chemical composition. The concept of surface-anchored polymer assemblies is employed in several projects, including, study of the mushroom-to-brush transition in surface-tethered polymers, monitoring kinetics of controlled/"living" radical polymerization, synthesis of surface-anchored copolymers with tunable compositions, and analysis of macromolecular conformations in weakly charged grafted polyelectrolyte and polyampholyte systems. We also discuss the application of grafted polymer gradient systems in studying three-dimensional dispersions of nanosized guest objects. In the aforementioned examples, the use of gradient structures both enables methodical exploration of a system's behavior and facilitates expeditious data measurement and analysis. Furthermore, we outline methods leading to the formation of orthogonal gradients-structures in which two distinct gradients traverse in orthogonal directions. We illustrate the applicability of molecular weight/grafting density orthogonal gradients in organizing nanoparticles and controlling protein adsorption on polymer surfaces. Finally, we identify several areas of science and technology, which will benefit from further advances in the design and formation of gradient assemblies of surface-bound polymers.