1. Degassed Water As a Cleaning Agent ? No Soap Needed 2005. 04. 27 Jihee Park

2.  Background

3.  Motive

4.  Contents [1]R. M. Pashley, P. M. McGuiggan, B.W. Ninham, and D. F. Evans, Science, 1985, 229, 1088-1089 [2]R. M. Pashley, J. Phys. Chem. B, 2003, 107, 1714-1720 [3]N. Maeda, K. J. Rosenberg, J. N. Israelachvili, and R. M. Pashley, Langmuir, 2004, 20, 3129-3137 [4]R. M. Pashley, M. Rzechowicz, L. R. Pashley, and M. J. Francis, J. Phys. Chem. B, 2005, 109, 1231-1238  References 1.Experimental results 2.Discussion for the principles 3.Conclusion

5.  Cleaning experiment RHS : de-gassed and sealed mixture LHS : nitrogen-equillibrated mixture  Degassing method Figure 1. Photograph of the cleaning water 1 min after vigorous shaking with gassed and degassed water [4] - Freezing water in a bottle with liquid N 2 - Pumping using a mechanical pump (pressure down to 0.01mbar) - Closing the bottle - Melting the water to room temperature  Repeating this process for 4 or 5 times  99.99% removal of dissolved gas

6.  Cleaning experiment Figure 2. Comparison of the turbidity of squalane and water mixtures with time after shaking, for degassed mixtures and after bubbling with nitrogen gas. [2]  NTU (Nephelometer Turbidity Units) - unit used to measure how much the hydrophobic particle or droplet is dispersed - 0.02 for distilled water and 1-5 for reservoir water  Nitrogen bubbling - to remove dissolved carbon dioxide and increase the pH value of the aqueous phase to 7, in agreement with that of the degassed samples

7.  Hydrophobic Force Figure 3. Estimated DLVO interaction energies between the two charged oil droplets in the 1 mM NaCl solution, under conditions with and without a typical hydrophobic attraction. [3] Hydrocarbon oils and finely divided hydrophobic particles will not readily disperse in water by this hydrophobic interaction.

8.  Gas Cavitations Figure 4. Schematic diagram of the detachment of an oil droplet from an oil/water interface. Dissolved atmospheric gas molecules will be drawn to the interface and assist the cavitations expected as two hydrophobic surfaces separate in water. [4]  Break away of oil droplet from oil bulk phase with mechanical disturbance  Hydrophobic surfaces approach each other  High surface energy between two hydrophobic surfaces induce the gas cavitations

9.  Cavity Bridging Figure 5. Schematic description of the air and vapor entrapment and attachment apparent from the results obtained with hydrophobic particles (or oil droplet) dispersions in water. [2]  Cavity bridging between the hydrophobic surfaces  Enhanced van der Waals attraction between the surfaces  Hold the surfaces together

10.  Break Off of the Fine Oil Droplets Figure 6. NTU values following degassing and spontaneous emulsification of the squalane droplets in water at pH 2, 7, and 11. [3] OH- Oil Water Figure 7. Schematic description of the break off of fine oil droplets from the water/oil interface. [3]  Increase of the electrostatic force between the droplets  Increase of stability of the dispersion

11.  Effect of Regassing Figure 8. Effect of reintroducing dissolved gas [2]  The observed stability of the emulsion to reintroduced dissolved gas implies that the electrostatic barrier generated between the fully equilibrated, and hence charged, oil droplet is sufficient to maintain stability, even with a hydrophobic attraction.

12.  Water Property Change Table 1. Summary of values for the electrical conductivity of water under various conditions [4] Figure 11. Effect of nitrogen gas purging on the electrical conductivity of de-gassed and ordinary distilled water.[4]  Conductivity

13.  Conclusions  Future Works Suggested  Degassed water cleaning system with detergent  Research for the physical properties of the degassed water ; Dielectric constant and boiling point of water 1.Hydrocarbon oils and finely divided hydrophobic particles will not readily disperse in water by the hydrophobic force. 2.Degassed water is more effective at dispersing hydrophobic dirt. This effect appears to be due to the reduction of natural cavitations. 3.Completely degassed water has significantly higher electrical conductivity.

14.  Degassed Oil Cleaning Figure 9. Difference in turbidity of gassed and de-gassed cleaning water minutes after vigorous shaking with de-gassed perfluorohexane "dirt" on glassware. [4]

15.  Applications Figure 10. Diagram of a system designed to clean by the sequential application of de- gassed solvent and de-gassed rinsing water [4]  This type of system offers effective detergent-free cleaning which should disperse and remove all hydrophobic and hydrophilic forms of dirt.