Nuclear quantum effects (NQEs) in water arise due to delocalization, zero-point energy (ZPE), and quantum tunneling of protons. Whereas quantum tunneling is significant only at low temperatures, proton delocalization and ZPE influence the properties of water at normal temperature and pressure (NTP), giving rise to isotope effects. However, the consequences of NQEs for interfaces of water with hydrophobic media, such as perfluorocarbons, have remained largely unexplored. Here, we reveal the existence and signature of NQEs modulating hydrophobic surface forces at NTP. Our experiments demonstrate that the attractive hydrophobic forces between molecularly smooth and rigid perfluorinated surfaces in nanoconfinement are ≈10% higher in H2O than in D2O, even though the contact angles of H2O and D2O on these surfaces are indistinguishable. Our molecular dynamics simulations show that the underlying cause of the difference includes the destabilizing effect of ZPE on the librational motions of interfacial H2O, which experiences larger quantum effects than D2O.
|Original language||English (US)|
|Number of pages||6|
|Journal||The Journal of Physical Chemistry Letters|
|State||Published - Jul 31 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): CRG2017
Acknowledgements: The authors thank Professor Vishwanath Dalvi and Mr. Deepak Bapat from the Institute of Chemical Technology (Mumbai, India) and Prof. Adri van Duin and Dr. Wei Zhang (The Pennsylvania State University, University Park, PA) for fruitful discussions. S.P. thanks Mr. Sankara Arunachalam (KAUST) for assistance with contact angle goniometry. H.M. and S.P. thank Mr. Kuang-Hui Li and Dr. Miaoxiang M. Chen from KAUST and Dr. Ravi Sharma (Principal, RS Science and Technology Consulting, LLC, Acton, MA) for assistance with the functionalization of mica surfaces with perfluorodecyltrichlorosilane (FDTS). The authors thank Mr. Xavier Pita (Scientific Illustrator at KAUST) for preparing Figure 1a and Dr. Michael Cusack and Dr. Virginia Unkefer (KAUST) for assistance in scientific editing. T.A.P. and A.S. acknowledge the Supercomputing Laboratory at KAUST in Thuwal, Saudi Arabia. Parts of the computer simulations in this work were performed as a user project at the Molecular Foundry, Lawrence Berkeley National Laboratory, supported by the Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy (DOE). Further computer simulations were performed at the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the DOE. S.H.D. acknowledges funding support from LabEX ENS-ICFP (ANR-10-LABX-0010 and ANR-10-IDEX-0001-02 PSL). H.M., T.A.P., and S.H.D. acknowledge KAUST Office of Sponsored Research Competitive Research Grant OSR-CRG2017-3415.