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5THE INFLUENCE OF VARIOUS FACTORS ON THE STRUCTURAL PROPERTIES OF
WATER
STEFAN TODOROV TODOROV
Assist. Prof., PhD, Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of
Sciences, 1784 Sofia, Bulgaria
LIDIA TODOROVA POPOVA
Assist. Prof., PhD, Institute of Solid State Physics, Bulgarian Academy of Sciences, 1784 Sofia,
Bulgaria
Abstract. In this paper we discuss the influence of various global environmentalfactors on the so-called structural properties of water related to its physical and chemical properties. Structural properties are determined at the molecular level by a statistically stable network of hydrogen bonds between water molecules. The value and distribution of these bonds are influenced by various factors subject to global changes, such as: pollution, radiation, electromagnetic fields, water penetration through porous materials (filtration), water saturation with air (aeration), etc. Some results of laboratory studies of water samples are presented.
Keywords: environment, water, hydrogen bonds, energy spectrum.
Due to global changes on our planet, including climate change, increased pollution as a result of human activities, etc., ecosystem parameters reflect these changes to a greater or lesser degree. Of course, due to the well-known Chatelier-Braun thermodynamic principle, processes occur in a system subject to external influences (in our case, an ecosystem) that reduce changes in the system subject to these influences. In other words, the ecosystem is capable of "self-protection". Studying and monitoring changes in ecosystem parameters in response to external forcing provides some basis for intelligent humane intervention. We use the method of energy spectra [1] to study the effects of various factors on natural waters and present some results on these influences. The water spectrum is affected by various factors such as: pollution, chemical impurities and environmental factors [2 - 4], radiation [5], electromagnetic fields, water penetration through porous materials [6], etc. The method of energy spectra utilizes the existence of Hydrogen energy bonds between water molecules. The Hydrogen bonds constitute a statistically stable net of interactions between the water molecules. They are the basis of understanding of the phenomenon called "structure of water" [7]. The Hydrogen bond forces are stronger than the Van-der-Waals forces and have a space orientation. They explain some anomalous properties of water [8] compared to other fluids, e.g. extension of the water volume at some negative temperatures etc., and also explain the water surface tension, water polarization and others.
Due to temperature fluctuations, the Hydrogen bonds are deformed, and thus their strength varies statistically around some mean value Ё. The probability distribution of Hydrogen energy bonds is called here energy spectrum f(E) of the water probe in consideration.
The measurement method uses the process of evaporation of a drop [9] taken from a test water sample. Evaporation is monitored at constant temperature, pressure and airflow rate. The observation is performed under a microscope by measuring at regular intervals the contact angle в between the droplet and the substrate on which it is placed, in our case we use the Mylar folio. This substrate was chosen because it is hydrophobic and transparent. To determine the contact angle in our measurements, we used Antonov's method [1]. In this method, the measurement of the angle в is reduced to the measurement of linear distances. More precisely, we measure the thickness of the dark ring that appears around the drop as a refraction pattern when light rays cross the contact area of the
drop with the substrate on which the drop is located. As a result of the data obtained, we plotted the distribution p(6) of the angle 0.
The following relationship between p(0) andf(E) can be proved:
f(E) = by(0)/ [1 - (1 +bE)2]1/2;
where b = I(1+cos0o)/o; ois the surface tension of the drop, I = 5,03.1018 m-2 is the density of water molecules in the surface layer, 0o is the initial contact angle of the drop.
The above formulas are used to calculate the probability distribution f(E) of the hydrogen bonding energies in the probe, using, the corresponding measured 0 - distribution function. In addition, along with thef(E) of the probe, it is convenient to consider the energy spectrum of the control probe, which is not affected by the specific factor in question. A sample of highly purified deionized water can be used as a control. The arithmetic difference between the probe spectrum and the control spectrum (differential spectrum) df(E) shows the deviations from the control distribution of hydrogen energy bonds under the influence of the factor under study.
The following are the experimental results obtained on the influence of four types of environmental factors on the structure of water with respect to some parameters of Hydrogen bonding energy distribution. Namely, the influence of pollution, radiation contamination and physical processes, such as the passage of water through the pores and the enrichment of water with air.
Figure 1 shows the differential spectrum of sewage taken from the treatment plant, i.e., the sample also contains bacteria, and the differential spectrum of deionized water exposed to y-radiation from Co-60 (65 Krad/h), treated for 2 min. In constructing the differential spectra, highly purified deionized water was used as a control sample. Three samples, the sample from the treatment plant, the sample irradiated with y-radiation, and the control sample, were measured simultaneously, after which the corresponding differential spectra were calculated, as shown in the figure.
60
40
20 -
-1-1-1-
0.11 0.12
,[eV]
80
0 -
-20
-40
0.09
Figure 1. Differential spectra with control deionized water. Square denote the deionized water after influence of у - radiation. Triangle denote water
from purification station.
One observes a clear change in the energy levels of the polluted water with respect to energy levels of Hydrogen bonds for pure water (control). The same applies to the sample exposed to у - radiation
where a definite peak of energy states for energies around 0,12 eV appear in contradistinction to untreated water. The Y-axis on Figure 1 is multiplied by constant, so the relative Y-values of different points are informative.
On Figure 2 the water energy spectrum is given of a sample after its transport through a filter. Filtration is a natural process occurring in ecosystems during the movement of water through the soil cover. In the laboratory it is experimented by the water penetration trough a nuclear filter with approximately 200 000 holes per square millimeter. The probe of deionized water penetrated through the holes of the filter with a velocity of penetration 1,43.10-3 m/s
On Y-axis the probability of a Hydrogen energy bond to take place is given. Thus the local maxima of the distribution correspond to more probable appearance of the Hydrogen bond energy values to be read on the X-axis. So the maximum probability of occupation of energy level around 0,9 eV for deionized water (control) is about 37%. The same values for the filtrated water (probe) are correspondingly around 0.11 eV and 20%.
The mean value of Hydrogen energy bond can be calculated for the deionized water and probe from Fig. 1 utilizing the distributions marked respectively by squares and triangles. The corresponding values are: 0,091 eV for the control and 0,107 eV for the probe with an error of 0,003 eV.
0.40 -
-0.05 -I-1-1-1-1-1-1-1-1-1-1-1-1-1-1
0.08 0.09 0.10 0.11 0.12 0.13 0.14
-E,[eV]
Figure 2. Energy spectrum of deionized water before filtration denoted by square, and after filtration denoted by triangle.
The process of aeration of water occurs naturally in ecosystems, e.g. during the rainfall the falling water drops are saturated with air, as well as by fountains and waterfalls. On Figure 3 the water energy spectrum of a laboratory saturated with air probe (deionized water) is given and it is compared to the energy spectrum of the same probe after the process of air saturation is completed. In laboratory the air saturation occurred for a probe of 50 ml of deionized water for a period of 10 min with a small aquarium water pump. One can see from Figure 3 that after aeration the highest peak of energy level occupation is shifted to higher energies.
Figure 3. Water energy spectra of deionized water before saturation with air by square, and after
saturation with air by triangle.
The material presented shows that the energy spectra of water are sensitive to environmental pollution, radiation and the physical processes of filtration and saturation of water with air. After some calibration of energy spectra, the energy spectrum measurement can serve as an additional tool for environmental monitoring.
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