Unfamiliar faces of the most unfamiliar substances: extraordinary activity of interfacial water on oil droplets

Water behavior at hydrophobic interfaces has been baffling scientists for over a century, ranging from chemistry, biology, materials science, geology, and engineering. Recent discoveries highlight the pivotal role of interfacial water, including the unusual chemistry of water microdopplets and contact with electrocatalytics.

A new study published in Nature systematically resolves disordered molecular structures and ultra-higher electrostatic fields (~40-90 mV/cm) at mesoscopic interfaces in oil water, overturning textbook assumptions about the “inert” properties of hydrophobic surfaces, opening up new revenus for catalysts, biomorphism, and green energy.

For decades, total frequency generation (SFG) spectroscopy has dominated interfacial water studies, but suffered from inherent limitations. Researchers are currently pioneering new approaches. Integrate high-resolution Raman spectroscopy with multivariate curve resolution (MCR) algorithms.

The first nanoscale resolution measurements of the interfacial layer in oil-water emulsions were achieved by separating the solute correlation (SC) spectral signals with an unprecedented signal-to-noise ratio.

Their key findings include:

Structural Disorder: The distinctive OH stretch shoulder at 3250cm⁻¹, which is characteristic of the tetrahedral hydrogen bond network, disappears at the end at the oil droplet interface, indicating a dramatic structural disorder. Molecular dynamics simulations revealed that approximately 25% of interfacial water molecules have boneless “free” OH groups that are inconsistent with the classical predictions of “icy ordered layers.” Ultra-high electric field: By analyzing the resonant redshift (3575cm⁻¹) of free OH bonds, the team quantifies the interfacial electrostatic field (40-90 mV/cm), comparable to a vigorous field of enzyme active sites (~100 mV/cm). These fields are directly correlated with the droplet ζ potential. ζ reduces the redshift from -60 mV to -20 mV, including charge distribution (e.g., hydroxide adsorption or oil-water charge transfer) as the main mechanism. Meaning of Catalyst: The calculations of transition state theory showed that such fields reduce the activation free energy by about 4.8 kcal/mol, promoting 3,000 times >3,000 times at room temperature. This provides a mechanical basis for water microdroplation (speed improvements of 10 days to 10-10°) and explains the catalystless redox reaction in catalytic electrocatalysts.

Discovering obstacles and huge electric fields can alter understanding of biological processes (protein aggregation, membrane interactions) and techniques such as triboelectric nanogenesis factors, atmospheric aerosol nucleation, water purification, and oil intoxication repair.

The paper, entitled “Water Structure and Electric Fields in Oil Droplet Interfaces,” was the work of a joint team led by Professor Weimin of Columbia University and Professor Theresa Head Gordon of Berkeley, California. The authors of the co-first are Dr. Lixue Shi and Dr. Allen Lacour, who have made significant contributions from Naiksin Chiang, Joseph Heindel, Xiaoqi Lang, and Ruoqi Zhao.