Water repelling molecules are said to be hydrophobic. The hydration – or formation of water interfaces around hydrophobic molecules – is important for many biological processes: protein folding, membrane formation, transport of proteins across an interface, the transmission of action potentials across membranes. It is involved as well in the process of creating mayonnaise, or in the fact that you can get rid of fat with soap. Hydrophobic interfaces although long studied, are poorly understood.
Nonlinear optics and light diffusion allow to see the unseeable.
Credit: © 2012 EPFL
Here's an amusing kitchen-table experiment to illustrate waters unusual properties: put a drop of pure insulating oil in a glass of pure, non-conducting water, and create an electric field using two wires hooked up to a battery. You'll see the oil move from the negative to the positive pole of the little circuit you've created. You have created charge in a mixture that was neutral, and a huge amount of it too, judging from the speed at which the droplets move. The same thing happens for gas bubbles in water; the phenomenon of charging applies to all hydrophobic/water interfaces.
- A century of debates -
It's not a new discovery; scientists have observed the phenomenon in the middle of the 19th century. But despite more than a century of research, the reason why such a huge electric charge exists is still the subject of heated debate.In an article published this week in Angewandte Chemie – a journal of reference in the field – EPFL scientist Sylvie Roke challenges a hypothesis put forward last spring in the same journal. With experimental proof to back her up, the holder of the Julia Jacobi chair in photomedicine makes her case: the phenomenon is not caused by the inevitable "impurities" present in oils, as her colleagues claim, but rather by certain intrinsic properties of the water molecules involved.
The precision of the observations "shows that negative charges exist even in a total absence of surface impurities, and thus the explanation put forward by my colleagues, which was derived from charge measurements and chemical titrations of the bulk liquids, doesn't hold up," says Roke. "We have developed a unique apparatus that can distinctly measure the interfacial structure of a layer on the sub-nanometer length scale that surrounds a droplet of oil in water. Thus, we can 'see' what is on the interface, and do not have to deduce it from comparing bulk properties, which is far less accurate."
Disproving a hypothesis isn't enough to explain a phenomenon, however. Roke is studying a promising avenue, that explores the intrinsic quantum nature of the water molecule itself, which might be responsible for the phenomenon. "The measurements we've made as part of this refutation could be used to try and prove this explanation," she says. "It's fascinating, because quantum effects (the smallest of the smallest) might be responsible for macroscopic charging effects that influence so many properties that relate to the functioning of the human body."
Sylvie Roke | EurekAlert!
Structured light and nanomaterials open new ways to tailor light at the nanoscale
23.04.2018 | Academy of Finland
On the shape of the 'petal' for the dissipation curve
23.04.2018 | Lobachevsky University
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
23.04.2018 | Physics and Astronomy
23.04.2018 | Physics and Astronomy
23.04.2018 | Trade Fair News