Preparation of transparent, conductive films by graphene nanosheet deposition on hydrophilic or hydrophobic surfaces through control of the pH value

This study used sodium borohydride to reduce graphene oxide to graphene nanosheets (GNS), which contain the carboxylic functional group that becomes carboxyl (-COOH) or carboxylate anion (-COO-)-type in the acid or alkaline environment, respectively. The GNS with didodecyldimethylammonium bromide (DDAB) particles becomes hydrophilic (A-GNS) or hydrophobic (B-GNS) in property, through control of the pH value, which can be dispersed efficiently in water or a water/THF medium to deposit on the hydrophilic (poly(acrylic acid-acryl amide)) or hydrophobic (polystyrene) substrate for preparing the transparent, conductive film (TCF) by spin coating. The DDAB particles can be removed by washing with nitric acid, and the optimal performances of the TCFs are then obtained (HA-GNS and HB-GNS). The surface electrical resistance of HA-GNS (1.5 x 10(3) Omega square(-1) at transmittance of 82%) is similar to that of HB-GNS (2.1 x 10(3) Omega square(-1) at transmittance of 81%), which demonstrated that, not only the hydrophilic, but also the hydrophobic surface can be chosen to prepare the TCF when the hydrophilic and hydrophobic GNS can be prepared.