Responsive Organometallic Polymer Grafts: Electrochemical Switching of Surface Properties and Current Mediation Behavior

Abstract

Quantitative adherence and friction measurements between atomic force microscopy (AFM) tips and reversibly oxidized and reduced poly(ferrocenyl dimethylsilane) (PFDMS) molecular layers grafted to Au are reported. Poly(ferrocenylsilanes) (PFSs) such as PFDMS owe their redox responsiveness to the presence of ferrocene units, bridged by substituted silicon units, in the main chain. Polymers were obtained by anionic polymerization, which allowed us to copolymerize sulfur containing end groups that facilitated grafting to Au surfaces. Electrochemical atomic force microscopy (ECAFM) was used to study adherence and friction as a function of the oxidation state of the polymer. Measurements of interfacial friction as a function of applied load on the nanoscale using Si(3)N(4) AFM tips revealed a reversible increase of the friction coefficient and adherence strength of the PFDMS layers with increasing oxidation state in NaClO(4) electrolytes. The variation of the electrolyte salts (NaClO(4) or NaNO(3)) allowed an assessment of surface counterion adsorption effects. Issues related to the interpretation of observed friction and adherence changes such as electrolyte anion-ferrocenium ion pair effects, and electrostatic forces due to tip surface charges are discussed. Unidirectional current flow was detected in cyclic voltammograms of the PFDMS layers in NaClO(4). This electrode rectification behavior could in principle be utilized for applications in thin film devices based on PFS films.

Redox-Induced Backbiting of Surface-Tethered Alkylsulfonate Amphiphiles: Reversible Switching of Surface Wettability and Adherence

“…12,13 Moreover, the bending transition triggered in the PFS-SO 3 − films may also change the friction between the surface and a counter surface, which would be a topic of great interest to study. 54,55 ■ ASSOCIATED CONTENT * S Supporting Information SEM image of the PS colloid used for pull-off forces in AFM ( Figure S1), XPS spectra and atomic concentration of the different elements in PFS-I and PFS-SO 3 − (Figure S2), cyclic voltammogram of PFS-I in a 0.1 M solution of NBu 4 PF 6 in acetonitrile ( Figure S3) and i−t curve for a PFS-I film ( Figure S4). The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b01105.…”

Disassembly of redox responsive poly(ferrocenylsilane) multilayers: The effect of blocking layers, supporting electrolyte and polyion molar mass

“…We propose that the large difference between perchlorate anions and the other anionic structures in PFS release kinetics is related to ion pairing (complexation) interaction with ferrocium groups. This can be rationalized based on the ionic radius of ClO À 4 and its high polarizability promoting interactions and ion pairing [43][44][45][46]. Nishiyama et al [43] showed the direct detection of ClO À 4 complexes with the ferrocenium moieties using in situ Fourier transform (FT) Raman spectroelectrochemistry.…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…The adherence and friction of the films were reversibly controlled from an oxidised state (high adhesion, high friction) to a reduced neutral state (low adhesion, low friction), with the gold substrate an electrode. 187 This electrode rectification behaviour could be useful in applications in thin film devices based on PFS films. Gold electrodes have also been modified by cathodic reduction of the Au substrates, immersed in a solution of imidazolium−functionalised PFS chains in the poly(ionic liquid), 1-ethyl-3-methylimidazolium ethyl sulfate.…”