Double Layer Forces: the Role of Molecular Solvents
(2010)- Abstract
- The dielectric continuum model has rightfully been and continues to be a major
workhorse for theory and modelling in Surface and Colloid Chemistry. Due to
the implicit description of water, entering only as a scaling constant for
charge-charge interactions, one would not expect it to work for short
distances. However, considerable evidence has been accumulated over the years
which shows that this is not the case, and the dielectric continuum model
gives a reasonable description sometimes on lengthscales which approach the
size of a water molecule!
A first part of this thesis concerns theoretical modeling of the salt
dependent water uptake of a... (More) - The dielectric continuum model has rightfully been and continues to be a major
workhorse for theory and modelling in Surface and Colloid Chemistry. Due to
the implicit description of water, entering only as a scaling constant for
charge-charge interactions, one would not expect it to work for short
distances. However, considerable evidence has been accumulated over the years
which shows that this is not the case, and the dielectric continuum model
gives a reasonable description sometimes on lengthscales which approach the
size of a water molecule!
A first part of this thesis concerns theoretical modeling of the salt
dependent water uptake of a complex between DNA and CTA
(hexadecyltrimethylammonium). The electrostatic component of the free energy
was treated at the Poisson-Boltzmann level. Despite the demanding conditions,
with high electric fields, low water content and complex geometry, the
dielectric description of water works. The agreement between theory and
experiment is quantitative.
To try to understand why the primitive model is working under such conditions,
double layer forces with an explicit description of the solvent have been
studied through Monte Carlo simulations. A simple and previously
well-characterized system of two infinite, like-charged plates with only
neutralizing counterions was chosen. The solvent was treated as
Lennard-Jones dipoles (Stockmayer fluid) and, for comparison, also at the
primitive model level. The forces between like-charged plates in the primitive
model agree qualitatively with the molecular solvent ones and the implicit
solvent gives a reasonable description of the dielectric screening. As
expected, the molecular solvent introduces extra effects, namely packing. The
phenomenon of ion-ion correlation attraction, i.e., the attraction of the two
like-charged plates, is also reproduced in a molecular solvent. One of the
studies includes an analysis of the regime between the dielectric continuum
model and the full explicit molecular solvent. This is done by progressively
reducing the size of the molecular solvent, doubling its number density, and
keeping the dielectric properties constant.
The comparison between the two solvent models requires being able to calculate
the dielectric constant for a general dipolar fluid. A simulation methodology
has also been developed and tested for this purpose. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/1681982
- author
- Pegado, Luis LU
- supervisor
- opponent
-
- Professor Delville, Alfred, Université d'Orléans
- organization
- publishing date
- 2010
- type
- Thesis
- publication status
- published
- subject
- keywords
- Dielectric continuum model, molecular solvent, Stockmayer fluid, electrical double layer, ion-ion correlations, Monte Carlo simulations, thermodynamic modeling, pressure curves, interaction free energy, packing effects
- pages
- 145 pages
- defense location
- Lecture hall C, Center for Chemistry and Chemical Engineering, Lund, Sweden
- defense date
- 2010-10-21 10:30:00
- ISBN
- 978-91-7422-252-4
- language
- English
- LU publication?
- yes
- id
- 5df21a32-f929-424e-b38f-a97396136a8f (old id 1681982)
- date added to LUP
- 2016-04-04 13:25:28
- date last changed
- 2018-11-21 21:13:54
@phdthesis{5df21a32-f929-424e-b38f-a97396136a8f, abstract = {{The dielectric continuum model has rightfully been and continues to be a major <br/><br> workhorse for theory and modelling in Surface and Colloid Chemistry. Due to <br/><br> the implicit description of water, entering only as a scaling constant for <br/><br> charge-charge interactions, one would not expect it to work for short <br/><br> distances. However, considerable evidence has been accumulated over the years<br/><br> which shows that this is not the case, and the dielectric continuum model <br/><br> gives a reasonable description sometimes on lengthscales which approach the <br/><br> size of a water molecule!<br/><br> <br/><br> A first part of this thesis concerns theoretical modeling of the salt <br/><br> dependent water uptake of a complex between DNA and CTA <br/><br> (hexadecyltrimethylammonium). The electrostatic component of the free energy <br/><br> was treated at the Poisson-Boltzmann level. Despite the demanding conditions,<br/><br> with high electric fields, low water content and complex geometry, the <br/><br> dielectric description of water works. The agreement between theory and <br/><br> experiment is quantitative.<br/><br> <br/><br> To try to understand why the primitive model is working under such conditions, <br/><br> double layer forces with an explicit description of the solvent have been <br/><br> studied through Monte Carlo simulations. A simple and previously <br/><br> well-characterized system of two infinite, like-charged plates with only <br/><br> neutralizing counterions was chosen. The solvent was treated as<br/><br> Lennard-Jones dipoles (Stockmayer fluid) and, for comparison, also at the <br/><br> primitive model level. The forces between like-charged plates in the primitive <br/><br> model agree qualitatively with the molecular solvent ones and the implicit <br/><br> solvent gives a reasonable description of the dielectric screening. As <br/><br> expected, the molecular solvent introduces extra effects, namely packing. The <br/><br> phenomenon of ion-ion correlation attraction, i.e., the attraction of the two <br/><br> like-charged plates, is also reproduced in a molecular solvent. One of the <br/><br> studies includes an analysis of the regime between the dielectric continuum <br/><br> model and the full explicit molecular solvent. This is done by progressively <br/><br> reducing the size of the molecular solvent, doubling its number density, and <br/><br> keeping the dielectric properties constant.<br/><br> <br/><br> The comparison between the two solvent models requires being able to calculate <br/><br> the dielectric constant for a general dipolar fluid. A simulation methodology <br/><br> has also been developed and tested for this purpose.}}, author = {{Pegado, Luis}}, isbn = {{978-91-7422-252-4}}, keywords = {{Dielectric continuum model; molecular solvent; Stockmayer fluid; electrical double layer; ion-ion correlations; Monte Carlo simulations; thermodynamic modeling; pressure curves; interaction free energy; packing effects}}, language = {{eng}}, school = {{Lund University}}, title = {{Double Layer Forces: the Role of Molecular Solvents}}, url = {{https://lup.lub.lu.se/search/files/6116448/1681990.pdf}}, year = {{2010}}, }