1.5 Tea Time Break: Nucleation in Capillary Phase Transitions
31
In a slit-like pore, in contrast, capillary condensation can be an activation process.
The system can remain in a metastable state in which the vapor separates two wetting
films on the pore walls even though the thermodynamically stable state is the gap
filled with liquid.
Strange things happen in a slit-like pore. The most acute example is condensation
and evaporation behavior of a condensable vapor in a slit-like pore of adjustable slit
width [40–42]. There the average density of the confined fluid in the slit (over a
given cross section across the slit width) can continually vary from that of the vapor
to that of the liquid under right circumstances [40–42]. How can this happen? The
first instinct would be to assume that the system in fact consisted of two droplets
on each slit wall that were separated by a thin layer of vapor. However, as detailed
in [42], such a simplistic explanation would encounter another problem of some
sort that cannot be accounted for (for example, what had happened to the van der
Waals forces if two droplets could truly be separated by a narrow gap of only a few
nanometers?).
In the end, it appears that the most logical explanation is to assume a diffusive
interface that is akin to a supercritical state [42]. Elliot and Voitcu showed that such
strange behavior could occur in a slit-like pore if the slit walls are curved, even
slightly so [43]. The implications of this fascinating phenomenon to nucleation are
not clear at this stage. It might or might not be related to nucleation in confined
spaces of fixed dimensions.
References
1. C.H. Whitson, M.R. Brule, Phase Behavior, Richardson (Society of Petroleum Engineers,
Texas, 2000)
2. R.P. Feynman, R.B. Leighton, M. Sands, The Feynman Lectures on Physics (Addison-Wesley,
Reading, Massachusetts, 1963)
3. F. Reif, Fundamentals of Statistical and Thermal Physics (McGraw-Hill Book Co., Singapore,
1965)
4. H.B. Callen, Thermodynamics and an Introduction to Thermostatistics (Wiley, New York,
1985)
5. D. Kashchiev, Nucleation (Oxford, UK, Elsevier Science & Technology, 2000)
6. J.N. Israelachvili, Intermolecular and Surface Forces, 2nd edn. (Academic Press, San Diego,
1991)
7. B.J. Murray, D. O’Sullivan, J.D. Atkinson, M.E. Webb, Ice nucleation by particles immersed
in supercooled cloud droplets. Chem. Soc. Rev. 41, 6519–6554 (2012)
8. N. Maeda, Nucleation curves of model natural gas hydrates on a quasi-free water droplet.
AIChE J. 61, 2611–2617 (2015)
9. N. Maeda, Nucleation curves of methane hydrate from constant cooling ramp methods. Fuel
223, 286–293 (2018)
10. A.S. Stoporev, A.Y. Manakov, L.K. Altunina, L.A. Strelets, V.I. Kosyakov, Nucleation rates of
methane hydrate from water in oil emulsions. Can. J. Chem. 93, 882–887 (2015)
11. A.S. Stoporev, A.P. Semenov, V.I. Medvedev, B.I. Kidyarov, A.Y. Manakov, V.A. Vinokurov,
Nucleation of gas hydrates in multiphase systems with several types of interfaces. J. Therm.
Anal. Calorim. 134, 783–795 (2018)
31
In a slit-like pore, in contrast, capillary condensation can be an activation process.
The system can remain in a metastable state in which the vapor separates two wetting
films on the pore walls even though the thermodynamically stable state is the gap
filled with liquid.
Strange things happen in a slit-like pore. The most acute example is condensation
and evaporation behavior of a condensable vapor in a slit-like pore of adjustable slit
width [40–42]. There the average density of the confined fluid in the slit (over a
given cross section across the slit width) can continually vary from that of the vapor
to that of the liquid under right circumstances [40–42]. How can this happen? The
first instinct would be to assume that the system in fact consisted of two droplets
on each slit wall that were separated by a thin layer of vapor. However, as detailed
in [42], such a simplistic explanation would encounter another problem of some
sort that cannot be accounted for (for example, what had happened to the van der
Waals forces if two droplets could truly be separated by a narrow gap of only a few
nanometers?).
In the end, it appears that the most logical explanation is to assume a diffusive
interface that is akin to a supercritical state [42]. Elliot and Voitcu showed that such
strange behavior could occur in a slit-like pore if the slit walls are curved, even
slightly so [43]. The implications of this fascinating phenomenon to nucleation are
not clear at this stage. It might or might not be related to nucleation in confined
spaces of fixed dimensions.
References
1. C.H. Whitson, M.R. Brule, Phase Behavior, Richardson (Society of Petroleum Engineers,
Texas, 2000)
2. R.P. Feynman, R.B. Leighton, M. Sands, The Feynman Lectures on Physics (Addison-Wesley,
Reading, Massachusetts, 1963)
3. F. Reif, Fundamentals of Statistical and Thermal Physics (McGraw-Hill Book Co., Singapore,
1965)
4. H.B. Callen, Thermodynamics and an Introduction to Thermostatistics (Wiley, New York,
1985)
5. D. Kashchiev, Nucleation (Oxford, UK, Elsevier Science & Technology, 2000)
6. J.N. Israelachvili, Intermolecular and Surface Forces, 2nd edn. (Academic Press, San Diego,
1991)
7. B.J. Murray, D. O’Sullivan, J.D. Atkinson, M.E. Webb, Ice nucleation by particles immersed
in supercooled cloud droplets. Chem. Soc. Rev. 41, 6519–6554 (2012)
8. N. Maeda, Nucleation curves of model natural gas hydrates on a quasi-free water droplet.
AIChE J. 61, 2611–2617 (2015)
9. N. Maeda, Nucleation curves of methane hydrate from constant cooling ramp methods. Fuel
223, 286–293 (2018)
10. A.S. Stoporev, A.Y. Manakov, L.K. Altunina, L.A. Strelets, V.I. Kosyakov, Nucleation rates of
methane hydrate from water in oil emulsions. Can. J. Chem. 93, 882–887 (2015)
11. A.S. Stoporev, A.P. Semenov, V.I. Medvedev, B.I. Kidyarov, A.Y. Manakov, V.A. Vinokurov,
Nucleation of gas hydrates in multiphase systems with several types of interfaces. J. Therm.
Anal. Calorim. 134, 783–795 (2018)