The impact of surfaces on the contiguous aqueous phase is generally thought to extend no more than a few water-molecule layers. We find, however, that colloidal and molecular solutes are profoundly excluded from the vicinity of hydrophilic surfaces, to distances up to several hundred micrometers. Such large zones of exclusion have been observed next to many different hydrophilic surfaces, and many diverse solutes are excluded. Hence, the exclusion phenomenon appears to be quite general. To test whether the physical properties of the exclusion zone differ from those of bulk water, several methods have been applied so far. NMR, infrared, and birefringence imaging, as well as measurements of electrical potential, viscosity, and UV-VIS and infrared-absorption spectra, collectively reveal that the solute-free zone is a physically distinct, more ordered phase of water. It is much like a liquid crystal. It can co-exist essentially indefinitely with the contiguous solute-containing phase. Indeed, this unexpectedly extensive zone may be a candidate for the long-postulated “fourth phase” of water considered by earlier scientists. The energy responsible for building this charged, low entropy zone comes from light. We found that incident radiant energy including UV, visible, and near-infrared wavelengths induce exclusion-zone growth in a spectrally sensitive manner. IR is particularly effective. Five-minute exposure to radiation at 3.1 µm (corresponding to OH stretch) causes exclusion-zone-width increase up to three times. Apparently, incident photons cause some change in bulk water that predisposes constituent molecules to reorganize and build the charged, ordered exclusion zone. How this occurs is under study. Photons from ordinary sunlight, then, may have an unexpectedly powerful effect that goes beyond mere heating. It may be that solar energy builds order and separates charge between the near-surface exclusion zone and the bulk water beyond — the separation effectively creating a battery. This light-induced charge separation resembles the first steps of photosynthesis. Indeed, this light-induced action would seem relevant not only for photosynthetic processes, but also for all realms of nature involving water and interfaces. The work outlined above was selected in the first cohort of NIH Transformative R01 awards, which will allow deeper and broader exploration. It was also selected as recipient the 2008 University of Washington Annual Lectureship. Each year, out of the University’s 3,800 faculty members, one is chosen to receive this award. Viewable here, the lecture presents the material in a lively manner, accessible to non-experts.
Posted on: Sat, 07 Sep 2013 16:07:03 +0000
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