Probing the Structure and Dynamics of End-Grafted Flexible Polymer Chain Layers by Combined Atomic Force−Electrochemical Microscopy. Cyclic Voltammetry within Nanometer-Thick Macromolecular Poly(ethylene glycol) Layers

Abstract

The combined atomic force-electrochemical microscopy (AFM-SECM) technique was used in aqueous solution to determine both the static and dynamical properties of nanometer-thick monolayers of poly(ethylene glycol) (PEG) chains end-grafted to a gold substrate surface. Approach of a microelectrode tip from a redox end-labeled PEG layer triggered a tip-to-substrate cycling motion of the chains' free ends as a result of the redox heads' oxidation at the tip and re-reduction at the substrate surface. As few as approximately 200 chains at a time could be addressed in such a way. Quantitative analysis of the data, in the light of a simple model of elastic bounded diffusion SECM positive feedback, gave access to the end-tethered polymer layer thickness and the end-to-end diffusion coefficient of the chains. The thickness of the grafted PEG layer was shown to increase with the chain surface coverage, while the end-to-end diffusion coefficient was found to be constant and close to the one predicted by Rouse dynamics. At close tip-substrate separation, slowing of the chains' motion, as a consequence of their vertical confinement within the tip-substrate gap, was observed and quantitatively modeled.

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].…”

Elektrochemische Rastermikroskopie zur direkten Abbildung von Reaktionsgeschwindigkeiten

“…[263] Zu erwähnen ist auch der Ansatz von Abbou et al zur Charakterisierung von Polymerketten, die an einem Ende an einer Oberfläche verankert und am anderen Ende mit einer Ferroceneinheit markiert sind. [264] Durch einen elektrisch leitfähigen Kraftsensor können die Schichten in Lösung kontaktiert werden. Es lassen sich an den wenige Nanometer dicken Monolagen SECM-Annäherungskurven aufnehmen, die die Beweglichkeit der Polymerketten widerspiegeln.…”

“…Daher ist den mit SFM gekoppelten Systemen eine wesentlich größere Bedeutung beizumessen. Die Entwicklung wurde entscheidend von Macpherson et al [135,309,[423][424][425][426][427] und Kranz et al [428][429][430][431] angestoßen und wird inzwischen auch von weiteren Gruppen betrieben, [231,233,[432][433][434][435][436][437] wobei sich die verfolgten Konzepte im Detail unterscheiden. Für unterschiedliche praktische Anwendungen bewährten sich die Sonden, die Kranz et al durch Beschichtung von SFM-Kraftsensoren mit Metallen und einer Isolatorschicht und nachfolgender Bearbeitung mit einen fokussierten Ionenstrahl (FIB, focused ion beam) erhielten.…”

Multidimensional electrochemical imaging in materials science

“…Indeed, the present consensus is that SAMs are collectively organized in different phases constrained by disordered boundaries and substrate defects [251]. The approach of Abbou et al [74] is also notableby use of the combined AFM-SECM technique they probed the structure and dynamics of polymer chains labeled on one end with a ferrocene unit and grafted on the other end to a gold surface.…”

“…Several comprehensive reviews [44,[47][48][49][50][51][52][53][54][55][56][57][58], books [45,59], and book chapters [60][61][62][63][64][65][66][67] are available about this technique; the reader is referred to these for detailed information about instrumental set-up, concept, measurement modes, and data interpretation. Besides approaches combining SECM with other scanning probe techniques, for example EC-STM [68][69][70][71] and AFM [72][73][74][75][76][77], the work of Schuhmann et al [78,79] popularized the use of a shear-force-based distance-control mechanism in the SECM community.…”