Controlling the Electrografting of Polymers onto Transition Metal Surfaces through Solvent vs Monomer Adsorption

Abstract

Electropolymerization of methacrylic monomers opens the possibility of chemically grafting a wide range of polymers onto transition metal surfaces. In this work, the electropolymerization of polyacrylonitrile and polyethyl acrylate is studied in different solvents; we experimentally confirm that the choice of solvent is a critical parameter for obtaining electrografted polymers. A density-functional theory−based study modeling the interaction of solvent (acetonitrile, dimethylformamide, and pyridine) or monomer (acrylonitrile and ethyl acrylate) molecules with the Ni(100) metal surface provides the means to classify the organic molecules with respect to their ability to interact with the surface. The surface binding-energy difference between monomer and solvent is introduced in a Frumkin-type isotherm. This allows us to rationalize the experimental observations in terms of a competitive adsorption at the metal surface between the monomer and the solvent. The first step in the electrografting mechanism thus appears to be the chemisorption of the monomer at the electrode surface before cathodic polarization is applied; the chemisorbed monomer is therefore the first species reduced, giving rise to an adsorbed reactive intermediate, which is thus able to start the polymerization of a grafted chain.

Adsorption of Block Copolymers from Selective Solvents on Curved Surfaces

“…(a) If we assume that the first term in the square brackets in eq 7 is larger than the second, then we get (9) (b) If we assume that the repulsion between the blocks (second term in eq 7) is the dominant factor in the spreading of the drops, then we obtain (10) On the basis of these expressions, we define a new parameter ∈, the polymeric control parameter, to be N B /N A 11/6 in the first limit (eq 9), or N B /N A 5/6 in the second limit (eq 10). In both these equations, Ψ is a correction term that depends only on the monomeric interfacial energies and on the particular geometry of the adsorption morphologies.…”

“…[6][7][8][9][10][11] Moreover, the polymer adsorption is facilitated by an interaction-multiplier effect, which is unique to chain molecules. [12][13][14] Any interaction that occurs with one segment is multiplied by the large number of identical segments in the macromolecule to generate a large intermolecular effect.…”

Electrodeposition of mixed adherent thin films of poly(ethyl acrylate) and polyacrylonitrile onto nickel

“…That the grain size increases with monomer concentration is not the consequence of an increase in the chain grafting density. Indeed, Crispin et al have shown [14] that AN is much more strongly adsorbed onto Ni than the solvent molecules. This suggests that when the nickel electrode is put in the electrochemical medium the 6 metal surface gets covered by a monolayer of AN molecules, whatever the solvent and the AN concentration.…”

“…Solvation of the PEA chains by the electrolytic solution (AN/DMF) is only part of the explanation. According to theoretical calculations by Crispin et al [14], EA is less strongly adsorbed onto nickel than AN and thus less prone than AN to displace the solvent molecules for being adsorbed onto the cathode sites. Thus, the Ni surface, which is thought to be covered by a monolayer of AN molecules in DMF, would not be completely covered by EA at the same concentration (0.5 M) in DMF.…”

“…In an effort to understand the origin of this restriction, dependence of the electrochemical reaction on the composition of the conducting solution (mainly conducting salt and solvent) has been studied [8]. Success or failure in the grafting reaction appear to be actually controlled by a strong competition between solvent and monomer for adsorption onto the cathode in the very first step of the process [13,14]: provided that the solvent is judiciously chosen, it is possible to graft onto the cathode a series of acrylic and methacrylic monomers. In these cases, voltammograms with two typical peaks are recorded, and adherent films are formed on the metal in the potential range of peak I.…”