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Posted:
10 years ago
15 apr 2015, 01:33 GMT-4
I understand that the nanochannel resides between two spaces on the bottom and top of your plots. In those volumes electroneutrality does not hold, the conc. of anions is ca. 50 mM and that of cations ca. 35 mM on the bottom and ca. 80 mM on the top. Electroneutrality does not hold in the electrical double layer but that is only a few nanometers thick in those concentrations; you have neither given the geometric dimensions.
To me it looks that the surface is positively charged as anions are accumulating on the wall and cations are repelled - provided that I understood correct where your channel is in the pictures. But whatever is the model, electroneutrality must hold in the bulk of the solution.
br
Lasse
I understand that the nanochannel resides between two spaces on the bottom and top of your plots. In those volumes electroneutrality does not hold, the conc. of anions is ca. 50 mM and that of cations ca. 35 mM on the bottom and ca. 80 mM on the top. Electroneutrality does not hold in the electrical double layer but that is only a few nanometers thick in those concentrations; you have neither given the geometric dimensions.
To me it looks that the surface is positively charged as anions are accumulating on the wall and cations are repelled - provided that I understood correct where your channel is in the pictures. But whatever is the model, electroneutrality must hold in the bulk of the solution.
br
Lasse
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Posted:
10 years ago
15 apr 2015, 09:51 GMT-4
Thank you for your reply ! First, you are right, the surface has a positive charge of 0.05 C/m^2, The diameter of the channel is 4 nm. The Domain is as follows = There is a large bulk concentration of ions in the 'Inlet container', and no concentration in the channel and the other container. The time-dependent behaviour of this is studied. I have attached another picture that has details about the geometry. Again, thank you !
Thank you for your reply ! First, you are right, the surface has a positive charge of 0.05 C/m^2, The diameter of the channel is 4 nm. The Domain is as follows = There is a large bulk concentration of ions in the 'Inlet container', and no concentration in the channel and the other container. The time-dependent behaviour of this is studied. I have attached another picture that has details about the geometry. Again, thank you !
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Posted:
10 years ago
16 apr 2015, 05:19 GMT-4
Hi
In 0.118 M concentration the Debye length is only ca. 1 nm. Hence I do not believe that your model in entirely correct (neither entirely incorrect :)). Charge density is proportional to the difference of cation and anion concentrations in Poisson-Boltzmann equation. Have you looked at that or the potential distribution? Charge relaxations take place is nanoseconds, i.e. electroneutrality should prevail beyond 1 nm from the surface at all times. And in the inlet and outlet compartment there is no surface charge, hence there is no charge separation. How long does it take to exchange the entire liquid volume? Your plot was at t = 1000 ns.
br
Lasse
Hi
In 0.118 M concentration the Debye length is only ca. 1 nm. Hence I do not believe that your model in entirely correct (neither entirely incorrect :)). Charge density is proportional to the difference of cation and anion concentrations in Poisson-Boltzmann equation. Have you looked at that or the potential distribution? Charge relaxations take place is nanoseconds, i.e. electroneutrality should prevail beyond 1 nm from the surface at all times. And in the inlet and outlet compartment there is no surface charge, hence there is no charge separation. How long does it take to exchange the entire liquid volume? Your plot was at t = 1000 ns.
br
Lasse
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Posted:
10 years ago
16 apr 2015, 15:32 GMT-4
Haha, yeah. This would be better modeled as discrete ions, but what I'm essentially trying to do is make a continuum approximation. Actually, I only ran the model for 1000 ns as, there seems to be no change in concentration distribution than the images that I've plotted after about 800 ns or so. Would you like to take a look at my model ? I will attach it as soon as I get to the computer where I've saved it.
Haha, yeah. This would be better modeled as discrete ions, but what I'm essentially trying to do is make a continuum approximation. Actually, I only ran the model for 1000 ns as, there seems to be no change in concentration distribution than the images that I've plotted after about 800 ns or so. Would you like to take a look at my model ? I will attach it as soon as I get to the computer where I've saved it.
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Posted:
10 years ago
17 apr 2015, 01:25 GMT-4
I can have look at it if you send it.
br
Lasse
I can have look at it if you send it.
br
Lasse
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Posted:
10 years ago
17 apr 2015, 12:14 GMT-4
My file size was too big, and I had to clear my solutions to make it small enough to attach here. You would be able to see that there is also a Laminar Flow physics module used in the model, but it is disabled on purpose. The Poisson Boltzmann's equation is a Steric-modified equation set based on this:
www.academia.edu/3220012/Steric_Effects_in_Electrolytes_A_Modified_Poisson-Boltzmann_Equation
Thank you !
My file size was too big, and I had to clear my solutions to make it small enough to attach here. You would be able to see that there is also a Laminar Flow physics module used in the model, but it is disabled on purpose. The Poisson Boltzmann's equation is a Steric-modified equation set based on this: http://www.academia.edu/3220012/Steric_Effects_in_Electrolytes_A_Modified_Poisson-Boltzmann_Equation
Thank you !
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Posted:
10 years ago
18 apr 2015, 12:12 GMT-4
You have plenty of issues with the units. Also, I would not define variables but global parameters. I suspect that because your units are not matching, the exponential functions are overshooting seriously, giving physically meaningless results.
br
Lasse
You have plenty of issues with the units. Also, I would not define variables but global parameters. I suspect that because your units are not matching, the exponential functions are overshooting seriously, giving physically meaningless results.
br
Lasse
