Scanning Electrochemical Microscopy: Principles and Applications for the Manipulation of Polymer Brushes

Abstract

Insulating Surfaces-Transient SECM Analysis ........ 185 8.4Observing and Tuning Reactivity with SECM and PolymerBrushes .......................................................................................................187 8.4.1 Context............................................................................................. 187 8.4.2Polymer Brushes a Mechanistic Tool for the Interrogationof Surface Reactivity ...................................................................... 188Over the past two decades surface-anchored polymer chains, also known as polymer brushes, have been tremendously used to create smart or responsive interfaces or surfaces. Indeed, as one end of the macromolecular chain is tethered to the surface while the other is freely moving in solution, polymer brushes present very interesting properties based on their ability to reorganize upon environmental changes.1 It is then possible to trigger the alteration of the chain’s conformation upon a wide range of stimuli: pH, ionic strength, electrical, thermal, photo-or electrochemical actuations. It explains the increasing number of applications using polymer brushes, ranging from the design of thermo-or solvent-responsive materials to materials for the design of biosensors for diagnostics or for drug delivery.2,3 The most efficient route to generate thick polymer brushes with high grafting densities is afforded by surface-initiated polymerizations where the polymerization is directly processed from initiators of polymerization anchored to surfaces. Among these grafting from living polymerizations, the method of choice is likely the highly controlled atom transfer radical polymerization (ATRP). It allows the generation of dense architectures of polymer brushes with a maximum control over brush density and polydispersity.4-10Surfaces tethered with such controlled polymer brushes and their stimuli-responsive behaviors have been characterized using a large number of techniques that have been recently reviewed.4 Among them, electrochemical techniques are particularly appealing as they could be used both for the characterization of the materials and for their actuation. For instance, polymer brushes are appealing materials for the design of electrochemical biosensors. In this context, polymer brushes are commonly characterized by8.4.2.1 Principle ............................................................................ 188 8.4.2.2Chemical Reactivity of a Self-AssembledMonolayer.......................................................................191 8.4.2.3 Chemical Reactivity in Thicker and DisorderedLayers ................................................................................ 194 8.4.3 Patterning Surfaces with Polymer Brushes by SECM .............. 1958.4.3.1Positive Transfer of Polymer Brush Patterns by SECM................................................................................ 1958.4.3.2 Negative Transfer of Polymer Brush Patterns by SECM ................................................................................ 1978.4.3.3 Local (Electro-)Chemical Functionalization of Polymer Brushes.............................................................. 1988.4Outlook and Conclusion ........................................................................... 199 References .............................................................................................................200