References
143
nucleation rates of clathrate hydrates across various systems of different scales and
complexity, which in turn has been limiting the ability of the researchers to study
the nucleation process itself. The understanding of all the other aspects of nucleation
can only follow, not precede, the determination of nucleation rates.
Nucleation of any system is intrinsically an interfacial phenomenon. It is therefore impossible to understand nucleation phenomena without understanding relevant
interfacial phenomena. One of the main themes of this book is to underscore this
salient, if obvious, point. Heterogeneous nucleation of gas hydrates requires not
only a solid substrate that could lower the nucleation work and the activation barrier
but also ample supplies of guest gases in its vicinity. This unique attribute of gas
hydrate systems renders interfacial gaseous states the key interfacial phenomena in
the heterogeneous nucleation of gas hydrates. Once we grasp this salient point, the
long-standing mystery in gas hydrate nucleation—the memory effect—may become
understandable, at least qualitatively. Unfortunately, it still remains unclear how the
homogeneous nucleation work and activation barrier are related to the heterogeneous
nucleation work and activation barrier in terms of specific interfacial free energies
of gas hydrates. It thus appears that a new and comprehensive theory is required for
gas hydrate nucleation. It is not clear at this stage how such a new and comprehensive theory might look like, but it appears incorporation of the disjoining pressure of
interfacial gaseous states would be necessary.
Several pieces of the puzzle started falling into place, one by one, and we are
now approaching a stage that elucidating more complex and sophisticated aspects of
clathrate hydrate nucleation is becoming feasible. We now have at least established
a systematic, reliable, and statistically robust technology for the determination of
nucleation rates of clathrate hydrates. We also established scaling laws for nucleation
rates of clathrate hydrates that enable comparison of nucleation rates of multiple
systems of different scales and complexities. At an empirical level, we are about to
establish that, unlike in any other systems, the total length of the three-phase lines
is the appropriate measure of the system size for clathrate hydrate nucleation when
a solid wall is present. Practically, these findings are expected to have substantial
impacts on future applications of gas hydrate nucleation, like risk management in
flow assurance of oil and natural gas pipelines, strategic selections, and blending
strategies of the Pickering agents for generation of dry water. Fundamentally, this
issue will need to be coherently resolved in the yet-to-exist comprehensive theory.
The interplay between the hydrogen bonding of water, hydrophobic hydration of
non-polar guest gases, hydration of ions in electrolytes, the impact of solid walls and
the surface forces, the impact of confinement and capillarity, nucleation of a second
gas hydrate phase in the presence of one, among a myriad of other issues, remain
open. It is our hope that new insights gained from the investigations of nucleation of
clathrate hydrates will eventually shed new light to our understanding of nucleation
of ice that has its own outstanding issues and mysteries.
We will end this book with one of the famous quotes of Winston Churchill; Now,
this is not the end. It is not even the beginning of the end. But it is, perhaps, the end
of the beginning.
143
nucleation rates of clathrate hydrates across various systems of different scales and
complexity, which in turn has been limiting the ability of the researchers to study
the nucleation process itself. The understanding of all the other aspects of nucleation
can only follow, not precede, the determination of nucleation rates.
Nucleation of any system is intrinsically an interfacial phenomenon. It is therefore impossible to understand nucleation phenomena without understanding relevant
interfacial phenomena. One of the main themes of this book is to underscore this
salient, if obvious, point. Heterogeneous nucleation of gas hydrates requires not
only a solid substrate that could lower the nucleation work and the activation barrier
but also ample supplies of guest gases in its vicinity. This unique attribute of gas
hydrate systems renders interfacial gaseous states the key interfacial phenomena in
the heterogeneous nucleation of gas hydrates. Once we grasp this salient point, the
long-standing mystery in gas hydrate nucleation—the memory effect—may become
understandable, at least qualitatively. Unfortunately, it still remains unclear how the
homogeneous nucleation work and activation barrier are related to the heterogeneous
nucleation work and activation barrier in terms of specific interfacial free energies
of gas hydrates. It thus appears that a new and comprehensive theory is required for
gas hydrate nucleation. It is not clear at this stage how such a new and comprehensive theory might look like, but it appears incorporation of the disjoining pressure of
interfacial gaseous states would be necessary.
Several pieces of the puzzle started falling into place, one by one, and we are
now approaching a stage that elucidating more complex and sophisticated aspects of
clathrate hydrate nucleation is becoming feasible. We now have at least established
a systematic, reliable, and statistically robust technology for the determination of
nucleation rates of clathrate hydrates. We also established scaling laws for nucleation
rates of clathrate hydrates that enable comparison of nucleation rates of multiple
systems of different scales and complexities. At an empirical level, we are about to
establish that, unlike in any other systems, the total length of the three-phase lines
is the appropriate measure of the system size for clathrate hydrate nucleation when
a solid wall is present. Practically, these findings are expected to have substantial
impacts on future applications of gas hydrate nucleation, like risk management in
flow assurance of oil and natural gas pipelines, strategic selections, and blending
strategies of the Pickering agents for generation of dry water. Fundamentally, this
issue will need to be coherently resolved in the yet-to-exist comprehensive theory.
The interplay between the hydrogen bonding of water, hydrophobic hydration of
non-polar guest gases, hydration of ions in electrolytes, the impact of solid walls and
the surface forces, the impact of confinement and capillarity, nucleation of a second
gas hydrate phase in the presence of one, among a myriad of other issues, remain
open. It is our hope that new insights gained from the investigations of nucleation of
clathrate hydrates will eventually shed new light to our understanding of nucleation
of ice that has its own outstanding issues and mysteries.
We will end this book with one of the famous quotes of Winston Churchill; Now,
this is not the end. It is not even the beginning of the end. But it is, perhaps, the end
of the beginning.