Structures of Filtered Water
Water possesses a variety of molecular structures based on the components of water. These structures significantly affect the physical properties, such as surface tension, electrical conductivity and molecular size, which in turn would have a great impact on our health if the water is consumed in our bodies.

Freezing is the only sample preparation method available to image water, and Low Temperature/Cryogenic Scanning Electron Microscopy (SEM) is used to demonstrate the structures of the water based on its components at the time when the water is frozen from room temperature at a very high rate in liquid nitrogen slush (-207∞C). During freezing, most of the solutes (components) are pushed to the ice crystal boundaries and some of the solutes are trapped within the ice crystals. Consequently, depending on the composition of the solutes, much of the image features in the frozen water are defined by the identifiable pattern of solutes and ice crystals.

Recently, the structures of various water samples were examined in the Cryogenic Scanning Electron Microscope at the Department of Food Science, University of Guelph. These water samples were initially contained in a rivet which was then frozen in liquid nitrogen slush to provide a very similar fast freezing rate. The frozen samples were then sublimed at -80∞C, a standard freeze drying temperature, for 1 hour to remove the free water on the sample surface. After sublimation was complete, the samples were coated with 30 nm of gold to provide secondary electrons as the primary signal for scanning electron microscope (SEM) imaging. The solutes remaining on the crystal boundaries or in the crystals reveal the structure of the water at the time of freezing.

The SEM photographs of the structures of tap water, the filtered tap water with one of a brand name filters, and the Crystal-Ki filtered water are shown in Figure 1. Figure 2 shows the SEM photographs of the structures of a spring water sample and its filtered water with Crystal-Ki. The results show that each sample is characterized by its own distinct structure, and that the tap water reveals the most solutes and the Crystal-Ki filtered water seems to have the smallest crystals and the tightest lattice or cross-linked network of solutes.

Click any of the images for a full screen image

Figure 1. SEM photographs of the structures of tap water and its filtered water with a brand name filter and Crystal-Ki. The magnification is indicated by the dotted line.
     
  Figure 1a. Tap Water This water was obtained from Guelph, Ontario which is considered to be heavily chlorinated and hard water (containing a lot of minerals or solutes). Large solutes align in the direction of freezing to form freeze lines. Small solutes distribute heavily and evenly between the freeze lines.
     
  Figure 1b. Filtered tap water with one of the brand name filter. - Solutes align themselves in the direction of freezing revealing a coarse lattice or cross-linked network as the water was removed by sublimation. Very few trapped solutes are seen in the network.
     
  Figure 1c. Filtered tap water with Crystal-Ki filter. - The structure shows a very close and tight lattice or lace liked cross-linked network of solutes when compared with the structure of the filtered tap water with one of the brand filter as shown in Fig. 1b.
     
Figure 2. SEM photographs of the structures of spring water and its filtered water with Crystal-Ki filter. The magnification is indicated by the dotted line.
     
 

Figure 2a.
Spring water. - Solutes distribute evenly throughout the sample, and no freeze lines are seen. The structure is quite different from that of the tap water.
     
  Figure 2b.
Filtered Spring water with Crystal-Ki. - Fewer solutes are seen (solutes are removed from the spring water), and solutes are pushed to the ice crystal boundaries to reveal the cross-linked network after the water is removed by sublimation. The structure also shows a close and tight lattice.

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Surface Tension Measurements of Crystal Ki Water

Summary:
The surface tensions of four (4) water samples, namely Crystal Ki Bottled Water, Crystal Ki Filtered Water, spring water and tap water, in contact with air were determined in this investigation. Water droplets were initially prepared on a flat polished silicon plate. The images of the water droplets were taken with the use of a high resolution digital camera at the Department of Physics, University of Guelph. The images were then digitized to generate the droplet profile data for surface tension calculations. The calculations were preformed by Dr.S.W. Ip with the use of a computer program developed at the University of Toronto. The software program is based on Laplace Equation which relates the shape of the droplet to the surface tension. The average surface tensions of Crystal Ki Bottled and Crystal Ki Filtered waters are 64 ± 0.57 and 62 ± 1.48 mN/m respectively. The surface tensions of the spring water and the control sample, tap water, are 71.7 ± 2.4 and 74.1 ± 5.23 mN/m respectively. It is evident that the surface tensions of the Crystal Ki Bottled and Filtered water samples are lower than that of pure water. The decrease in surface tension might be attributed to the clustering of water molecules or the introduction or removal of certain solutes as water was passing through the Crystal Ki filter.

Procedure:
The water samples investigated in the present study were the same samples prepared in the previous microscopic study. A syringe was rinsed and cleaned with the tested water sample three times to avoid contamination before it was used to form a water droplet on a piece of flat polished silicon plate. The photographs of the droplets with a piece of metal bar of known dimension for magnification determination were taken by a high resolution digital camera. Two droplets were prepared for each water sample. The images of the droplets were then digitized with CorelDraw to produce the droplet profile data in terms of (x,y) values as the input date for the surface tension calculation program. The calculation program is essentially a curve fitting program, and it involves the simultaneous integration of three differential equations.

Results:
Figure 1 is the photograph showing one of the droplet images of the Crystal Ki Bottled water.

The calculated surface tensions, average surface tensions and standard deviations of the four water samples are summarized in Table 1. The average surface tension and the standard deviation for each sample are presented graphically in Figure 2.

Fig. 1. Photograph of the Crystal Ki Bottled Water droplet on a silicon substrate. A piece of metal bar with known dimension above the droplet is used to determine the actual size of the droplet for surface tension calculation. This photograph also shows the reflection of the droplet on the bottom for contact angle determination.

 

Table 1. Summary of the calculated surface tensions, average surface tensions and standard deviations of the four water samples.
Surface Tension (mN/m) Avg. Surface Tension,mN/m S.D., mN/m
Crystal Ki Bottled Water 64.40 63.60 64 0.57
Crystal Ki Filtered Water 63.00 60.90 61.95 1.48
Spring Water 73.40 70.00 71.7 2.4
Tap Water 77.80 70.40 74.1 5.23
 

Fig. 2. Average surface tensions of Crystal Ki Bottled Water, Crystal Ki Filtered Water, Spring Water and Tap Water.


Discussion and Conclusions:
CRC Handbook shows that increasing most chloride, carbonate and sulphate solutes in water would increase the surface tension of water from 72.75 mN/m (pure water) to 74 mN/m at 20∞C when the solute contents increase to 3 weight percent. The surface tension of the control sample, tap water which is also expected to contain low concentrations of these inorganic solutes, was determined to be 74.10 ± 5.23 mN/m. Therefore, it is in the same magnitude as the values reported in CRC Handbook, and it is expected that the surface tensions obtained in the present investigation are accurate.

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