Sum-Frequency Vibrational Spectroscopic Studies of Polymer/Graphene Interface

The interest in alignment of polymer on graphene surfaces has been motivated by a desire to gain a fundamental understanding the interaction between molecule and graphene, and for possible application of graphene for surface chemistry. Graphene-polymer interactions also play an important role in graphene-polymer composites, which exhibit greatly improved electrical conductivity, strength, and thermal stability compared with pure polymer material. Theoretical investigation of graphene-polymer interface has been performed previously using molecular dynamics simulations [1]. However, experimental studies of the interfacial characteristics of graphene-polymer composite has been challenging. Here we investigate the molecular orientation at polymer/graphene interface using phase-sensitive-sum-frequency generation spectroscopy. The sum-fequency spectrum shows clear vibration signatures of CH$_{2}$ groups. In particular, it suggests that CH$_{2}$ groups pointing toward the graphene surface interact with graphene strongly, which leads to a red shift of vibration frequency as large as 15 cm$^{-1}$. In this talk I will discuss the implications of our experimental findings. \\[4pt] [1] C. Lv, Q. Xue, D. Xia, M. Ma, J. Xie, and H. Chen, \textit{J. Phys. Chem. C}, \textbf{2010}, $114$ (14), 6588--6594.