On the Intrinsic Wettability of Graphene
Haitao Liu1, Zhiting Li1, Yongjin Wang2, Andrew Kozbial2, Lei Li2
1 Department of Chemistry, University of Pittsburgh, 2 Departmetn of Chemical and Petroleum
Engineering, University of Pittsburgh, Pennsylvania, USA
Graphene and graphite are long believed to be hydrophobic. Here we show that a
clean graphitic surface is in fact mildly hydrophilic [1]. We find that an as-prepared graphene
sample is hydrophilic with a water contact angle of ca. 40º. Upon exposure to ambient air,
the water contact angle gradually increased to ca. 60º within 20 min and plateaued at ca. 80º
after 1 day (Fig 1a). Infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS)
showed that airborne hydrocarbon adsorbed onto the graphene surface during this process
(Fig 1b). Both thermal annealing and controlled UV/O3 treatment removed the hydrocarbon
contaminants, which was accompanied by a concurrent decrease in the water contact angle.
Our findings show that graphene is more hydrophilic than previously believed and suggest
that the reported hydrophobic nature of graphene is due to unintentional hydrocarbon
contamination from ambient air.
Fig. 1. (a) Temporal evolution of the WCA measured on a graphene/copper sample. The
sample was taken out of the CVD chamber at time 0. The three photographs show the water drops
captured at 1 min, 60 min, and 1200 min. (b) ATR-FTIR spectrum of a graphene/copper sample. The
sample was taken out of the CVD chamber at time 0. The inset shows the integrated peak area vs time
for the peaks at 2930 cm-1 (asymmetric CH2 stretching, blue) and 2850 cm-1 (symmetric CH2
stretching, red).
References
[1] Zhiting Li, Yongjin Wang, Andrew Kozbial, Ganesh Shenoy, Feng Zhou, Rebecca McGinley, Patrick
Ireland, Brittni Morganstein, Alyssa Kunkel, Sumedh P. Surwade, Lei Li & Haitao Liu, Nature Materials,
12, 925-931, (2013).