Physics

Organic chemistry

Properties of water

Laser

Nonlinear optics

Terahertz radiation

Hydrogen bond

Analytical Chemistry (journal)

Optics

Absorption (acoustics)

Absorption spectroscopy

Density functional theory

Sum-frequency generation

Computational chemistry

Physical chemistry

Infrared spectroscopy

Chemical physics

Composite material

Absorption of water

Aqueous solution

Chemistry

Materials science

Sum frequency generation spectroscopy

Spectroscopy

Molecule

Molecular dynamics

Quantum mechanics

Optoelectronics

The Journal of Physical Chemistry Letters

Hydrophobicity/hydrophilicity of aqueous interfaces at the molecular level results from a subtle balance in the water-water and water-surface interactions. This is characterized here via density functional theory-molecular dynamics (DFT-MD) coupled with vibrational sum frequency generation (SFG) and THz-IR absorption spectroscopies. We show that water at the interface with a series of weakly interacting materials is organized into a two-dimensional hydrogen-bonded network (2D-HB-network), which is also found above some macroscopically hydrophilic silica and alumina surfaces. These results are rationalized through a descriptor that measures the number of "vertical" and "horizontal" hydrogen bonds formed by interfacial water, quantifying the competition between water-surface and water-water interactions. The 2D-HB-network is directly revealed by THz-IR absorption spectroscopy, while the competition of water-water and water-surface interactions is quantified from SFG markers. The combination of SFG and THz-IR spectroscopies is thus found to be a compelling tool to characterize the finest details of molecular hydrophobicity at aqueous interfaces.

Molecular Fingerprints of Hydrophobicity at Aqueous Interfaces from Theory and Vibrational Spectroscopies