High- versus Low-Quality Graphene: A Mechanistic Investigation of Electrografted Diazonium-Based Films for Growth of Polymer Brushes

Electrografting using aryldiazonium salts provides a fast and efficient technique to functionalize commercially available 3−5 layered graphene (vapour‐deposited) on nickel. In this study, Raman spectroscopy is used to quantify the grafting efficiency of cyclic voltammetry which is one of the most versatile, yet simple, electrochemical techniques available. To a large extent the number of defects/substituents introduced to the basal plane of high‐quality graphene by this procedure can be controlled through the sweeping conditions employed. After extended electrografting the defect density reaches a saturation level (∼1013 cm−2) which is independent of the quality of the graphene expressed through its initial content of defects. However, it is reached within fewer voltammetric cycles for low‐quality graphene. Based on these results it is suggested that the grafting occurs (a) directly at defect sites for, in particular, low‐quality graphene, (b) directly at the basal plane for, in particular, high‐quality graphene, and/or (c) at already grafted molecules to give a mushroom‐like film growth for all films. Moreover, it is shown that a tertiary alkyl bromide can be introduced at a given surface density to serve as radical initiator for surface‐initiated atom transfer radical polymerization (SI‐ATRP). Brushes of poly(methyl methacrylate) are grown from these substrates, and the relationship between polymer thickness and sweeping conditions is studied. Electrochemical reduction of an aryldiazonium salt is combined with atom transfer radical polymerization to develop a controllable and versatile method for attaching polymer brushes to graphene. The number of defect sites at graphene is shown to exert little impact on the final result.