Graphene Surface Energy by Contact Angle Measurements

Graphene has become an intensive research field of study in the material science due to its peculiar properties and various applications. Particularly, it is considered as the thinnest 2D material, which is used widely in many devices, and hence, this involves its interaction with supporting substrates; thus, free surface energy of graphene is very essential for its miscellaneous application in our life. Here, in this report, we present the measuring results of static contact angle of microscale liquid droplets adsorbed on graphene-coated copper and silicon substrates at room temperature to calculate the graphene surface free energy and its wettability. Both copper- and silicon-coated substrates increase the static water contact angle values, indicating hydrophobicity of graphene layers. On the other hand, variation of strength of aqueous ionic solution, sodium chloride solution, does not change the static water contact angle, indicating minor importance of polar component of surface free energy of graphene layers. For few layers of graphene, up to three, the graphene surface free energy is controlled by the Cassie state, while for more than three layers, the surface exhibits the Wenzel state of wetting.