Viscoelastic Properties of Electrochemically Deposited Protein/Metal Complexes

The interfacial gelation of proteins at metallic surfaces was investigated with an electrochemical quartz crystal microbalance (QCM). When Cr electrodes were corroded in proteinaceous solutions, it was found that gels will form at the Cr surfaces if molybdate ions are also present in the solution. Gelation is reversible and can also be controlled with the electrochemical potential at the electrode. Further, a method was developed to characterize the viscoelastic properties of thin films in liquid media using the QCM as a high-frequency rheometer. By measuring the frequency and dissipation at multiple harmonics of the resonance frequency, the viscoelastic phase angle, density-modulus product, and areal mass of a film can be determined. The method was applied to characterize the protein films, demonstrating that they have a phase angle near 55° and a density-modulus product of ≈10(7) Pa·g/cm(3). Data imply that the gels are composed of a weakly cross-linked proteinaceous network with properties similar to albumin solutions with concentrations in the range of ≈40 wt %.