Chemical Gating with Nanostructured Responsive Polymer Brushes: Mixed Brush versus Homopolymer Brush

Abstract

In this report, we describe a novel approach to create an electrochemical gating system using mixed polymer brushes grafted to an electrode surface, and we explore the switchable properties of these mixed polymer brushes. The morphological transitions in the mixed polymer brushes associated with the electrode surface result in the opening, closing, or precise tuning of their permeability for ion transport through the channels formed in the nanostructured thin film in response to an external stimulus (pH change). The gating mechanism was studied by atomic force microscopy, ellipsometry, contact angle measurements, force-distance measurements, and electrochemical impedance spectroscopy. In comparison to a homopolymer brush system, the mixed brush demonstrates much broader variation of ion transport through the thin film. We suggest that this approach could find important applications in electrochemical sensors and devices with tunable/switchable access to the electrode surface.

Self-organization of grafted polyelectrolyte layers via the coupling of chemical equilibrium and physical interactions

“…There is also a regime with solvent-filled holes (H) defects. These four different structures have been previously predicted (14,22,(25)(26)(27)(28)(29) and observed (4,12,14,17) in a variety of grafted systems. The region denoted as M þ NA corresponds to micelles together with highly stretched individual polymers and has never been observed before.…”

“…Grafted hydrophobic polymers tend to form domains because their chemical attachment to the surface does not enable macrophase separation; i.e., the chain molecules lack translational degrees of freedom. This effect has been observed in a variety of experimental realizations (4,(12)(13)(14)(15)(16)(17) and several applications for this interesting property have been devised that include nanopatterning (14), motion of nano-objects (15), and surfaces with switchable ionic permeability (4), redox activity (16), or friction properties (18). For grafted layers of weak polyacids like poly(methacrylic acid) or poly(vinyl pyridine), the attractions between polymer segments compete with the electrostatic repulsions that are regulated by the acid-base equilibrium.…”

“…A ubiquitous example of this competition in synthetic and life systems is the control of the charge state by protonation that regulates enzymatic activity (1), switches ionconductivity in biological (2) and synthetic channels (3), induces self-assembly (4)(5)(6)(7), and determines the properties of technologically important polyelectrolyte layers (8,9). These processes occur in confined inhomogeneous environments, where molecular organization is restricted and competition among interactions is augmented.…”

Smart surfaces with switchable superoleophilicity and superoleophobicity in aqueous media: toward controllable oil/water separation

“…On the other hand, the PDMS block has a desirably low glass transition temperature (Tg) of about À62 1C (according to the supplier), and it can be considered as a liquid-like polymer with high flexibility at ambient temperature. 26 In air, the liquid-like PDMS, which is more hydrophobic than the P2VP, can spontaneously move to the exterior of the grafted copolymer layer and dominantly expose itself to air. 37 As a consequence, hydrophobic PDMS on the exterior of the grafted block copolymer layer makes the surface hydrophobic, which is further amplified by the hierarchical micro-nanostructures on the surface, resulting in the superhydrophobicity.…”

From Self-Assembled Monolayers to Coatings: Advances in the Synthesis and Nanobio Applications of Polymer Brushes

“…Examples include the use of crosslinked or multiple-point grafted poly(glycidyl methacrylate) (PGMA) thin coatings or epoxy terminated silane SAMs to attach amine-or acid-terminated polymers [62][63][64][65][66][67][68], a reductive alkylation reaction between amine-functionalized surface and aldehyde-terminated polymers to form an imine bond which is subsequently reduced [69,70], Au-S bond formation between thiol-terminated polymer and Au surface [71,72], thiol-disulfide exchange reaction using thiol-terminated block copolymers to prepare for cleavable polymer brushes on silica particles [73,74], an amidation reaction of N-hydroxysuccinamde protected carboxylic acid terminated polymers and amine functionalized SAMs on surface [75], Diels-Alder ligation reaction between cyclopentadiene and maleimide [76], and a condensation reaction between silane-terminated polymers and silanol groups on an oxide surface [77].…”