X-Ray Decreases Surface Tension of Water (2008.5.29)
X-ray imaging shows in real-time and in in-vivo that intensive irradiation of x-rays significantly decreases the surface tension of water in droplets and capillary tubes.
X-rays are used in a variety of experimental studies of liquids, in particular, of water. The present synchrotron sources allow intense irradiation, possibly enabling to alter the basic property of surface tension. In spite of its potential impact, this issue has been still unexplored. In 1896 Wilson roughly showed that x-rays ionized the air molecules, and the electrons and ions created cloud nuclei in a cloud chamber. His cloud chamber was used to visualize ionizing radiation and opened up modern quantum physics. The x-ray-induced ionization of matter was studied in quantum physics through photoelectric effect and Compton scattering. In soft-matter physics, it was also known that electrostatic potential changes surface tension, as found by Lippmann in 1873. However, no one has ever observed the radiation effects on the surface tension of water. Professor Jung Ho Je and his research team from Korea, Switzerland, and Taiwan for the first time observed that xray- induced charge build-up leads to a large decrease of the effects of natural surface tension of water in droplets and capillary tubes. The team discovered the x-ray-induced surface tension reduction from direct experimental observations with phase contrast microradiology. The evidence was obtained with three different types of experiments at the 7B2 beamline of the Pohang Light Source (2.5 GeV, 150 mA storage ring in Pohang, Korea). Spatially-coherent synchrotron x-rays in the photon energy range 10-60 keV were used to irradiate water molecules and simultaneously to image the induced effects. They also developed a general physical model to link surface tension and surface ionization by unifying the related equations suggested by Lippmann and Rayleigh. This model successfully described the experimental observations that x-ray photons, by ionizing water molecules and creating charges, change the surface tension of water. The overall results showed a fundamental connection between ionizing radiation and surface tension. The team addressed that “the so far undetected phenomenon is explained by ionization and surface charge creation and can potentially affect many x-ray experimental techniques as well as different natural events.” In particular, this striking phenomenon might be an important issue due to current development of x-ray free-electronlasers with unprecedented brilliance. The research was published in May issue of Physical Review Letters, entitled, “Decreased surface tension of water by hard-x-ray irradiation”.
Professor Jung Ho Je
Department of Materials Science and Engineering