4.3 Is the Surface of Gas Hydrates Dry?
107
as opposed to the attractive van der Waals forces which suppress the thickness of
pre-melting layers on ice. Future experimental effort to the measurements of these
important fundamental quantities is essential before we can gain better insight.
4.4 Tea Time Break: Disjoining Pressure and Polywater
Polywater was a scientific scandal that engulfed the field of surface and interfacial
science in the late 1960s and the early 1970s. An excellent account of Polywater
was given by Franks [64]. As Franks noted, in their haste to disengage themselves
from the Polywater saga, the scientists in the field ignored many important scientific
questions raised by the Polywater.
One such important scientific question was; why did Polywater only form through
condensation of water vapor on quartz but not after prolong contact of liquid water
with quartz? Can water vapor possibly be more chemically reactive than the (denser)
liquid water? If so, how? The answer to this question was not known at the time Felix
Franks wrote his book in 1983, more than a decade after the closure of the Polywater
saga.
The most plausible explanation I have heard to the above question is as follows;
Derjaguin used low vacuum to control the vapor pressure of water. Since quartz is
hydrophilic, a thin film of water forms on a quartz surface at a low vapor pressure of
water, which will then thicken with increasing saturation of the vapor. Such thin films
of water are also encountered at an initial stage of the growth of a water film. The
disjoining pressure of a thin water film is positive and very large. It is conceivable
that the disjoining pressure was so large that it could crack the surface of the quartz
and unleash water-soluble components from within, which would not have occurred
with a direct contact of bulk liquid water with quartz, even after a long time.
The ultimate irony is that the concept of disjoining pressure was conceived by
none other than Derjaguin himself much earlier than the Polywater saga.
References
1. X.H. Zhang, X. Zhang, J. Sun, Z. Zhang, G. Li, H. Fang, X. Xiao, X. Zeng, J. Hu, Detection
of novel gaseous states at the highly oriented pyrolytic graphite-water interface. Langmuir 23,
1778–1783 (2007)
2. X.H. Zhang, N. Maeda, J. Hu, Thermodynamic stability of interfacial gaseous states. J. Phys.
Chem. B 112, 13671–13675 (2008)
3. X.H. Zhang, A. Khan, W.A. Ducker, A nanoscale gas state. Phys. Rev. Lett. 98 (2007)
4. X. Zhang, N. Maeda, Interfacial gaseous states on crystalline surfaces. J. Phys. Chem. C 115,
736–743 (2011)
5. B.V. Derjaguin, N.V. Churaev, V.M. Muller, Surface Forces (Consultants Bureau, New York,
1987)
6. P.G. de Gennes, F. Brochard-Wyart, D. Quéré, Capillarity and Wetting Phenomena (Springer,
New York, 2004)
107
as opposed to the attractive van der Waals forces which suppress the thickness of
pre-melting layers on ice. Future experimental effort to the measurements of these
important fundamental quantities is essential before we can gain better insight.
4.4 Tea Time Break: Disjoining Pressure and Polywater
Polywater was a scientific scandal that engulfed the field of surface and interfacial
science in the late 1960s and the early 1970s. An excellent account of Polywater
was given by Franks [64]. As Franks noted, in their haste to disengage themselves
from the Polywater saga, the scientists in the field ignored many important scientific
questions raised by the Polywater.
One such important scientific question was; why did Polywater only form through
condensation of water vapor on quartz but not after prolong contact of liquid water
with quartz? Can water vapor possibly be more chemically reactive than the (denser)
liquid water? If so, how? The answer to this question was not known at the time Felix
Franks wrote his book in 1983, more than a decade after the closure of the Polywater
saga.
The most plausible explanation I have heard to the above question is as follows;
Derjaguin used low vacuum to control the vapor pressure of water. Since quartz is
hydrophilic, a thin film of water forms on a quartz surface at a low vapor pressure of
water, which will then thicken with increasing saturation of the vapor. Such thin films
of water are also encountered at an initial stage of the growth of a water film. The
disjoining pressure of a thin water film is positive and very large. It is conceivable
that the disjoining pressure was so large that it could crack the surface of the quartz
and unleash water-soluble components from within, which would not have occurred
with a direct contact of bulk liquid water with quartz, even after a long time.
The ultimate irony is that the concept of disjoining pressure was conceived by
none other than Derjaguin himself much earlier than the Polywater saga.
References
1. X.H. Zhang, X. Zhang, J. Sun, Z. Zhang, G. Li, H. Fang, X. Xiao, X. Zeng, J. Hu, Detection
of novel gaseous states at the highly oriented pyrolytic graphite-water interface. Langmuir 23,
1778–1783 (2007)
2. X.H. Zhang, N. Maeda, J. Hu, Thermodynamic stability of interfacial gaseous states. J. Phys.
Chem. B 112, 13671–13675 (2008)
3. X.H. Zhang, A. Khan, W.A. Ducker, A nanoscale gas state. Phys. Rev. Lett. 98 (2007)
4. X. Zhang, N. Maeda, Interfacial gaseous states on crystalline surfaces. J. Phys. Chem. C 115,
736–743 (2011)
5. B.V. Derjaguin, N.V. Churaev, V.M. Muller, Surface Forces (Consultants Bureau, New York,
1987)
6. P.G. de Gennes, F. Brochard-Wyart, D. Quéré, Capillarity and Wetting Phenomena (Springer,
New York, 2004)