An Insight in the role of dopamine acted in the electroless deposition process using atomic force microscopy based single molecule force spectroscopy

Polydopamine (PDA) as a versatile coating material has attracted broad interest in the application of electroless deposition (ELD) due to its facile fabrication and abundant resources. The cross-linking density of PDA has an important effect on surface binding properties. Due to the complexity of cross-linked networks, however, it is still difficult to directly detect the cross-linking degree of polymers at a microscopic level. In this study, PDA coatings are measured at the single-molecule level by means of atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS). The obtained single peak (S-type) and multiple peak (M-type) force curves are used to define the typical force-extension (F-E) curves of the linear polymers with single chain and the cross-linked polymers with multiple chains, respectively. Furthermore, the as-prepared Cu plating PDA deposited PP substrate also exhibits excellent metallic conductivity in the deposition of DA for 16 h at the concentration of 0.02 M, which is in accordance with those from the SMFS results. Attributed to the scanning electron microscopy (SEM), fourier transform infrared spectrum (FTIR) and some other measurements, it further indicates that PDA with different cross-linking degrees using SMFS has proven the role as both reductive sites and binder in the ELD of Cu on polymer substrate. Besides, it is expected that AFM-based SMFS can be used as a general method to study different cross-linked polymers in the ELD and other surface modification processes.