Polyampholyteinduced repulsion between charged surfaces: Monte Carlo simulation studies
(2002) In Langmuir 18(16). p.64296436 Abstract
 The force between two planar charged surfaces in the presence of polyampholytes (PAs) is investigated as a function of the surface separation. The model system contains PA molecules with zero net charge adsorbing onto the charged surfaces from a dilute surrounding solution without salt. We compare the results obtained on three levels of approximation: (i) polyampholytes moving in the mean field due to the counterions, i.e., in the PoissonBoltzmann field, (ii) PAs in a selfconsistent field generated by both counterions and PA monomers, and (iii) with all interactions treated explicitly. Either the amount of PA is kept constant for varying slit widths or chemical equilibrium with a bulk solution is considered. The PA adsorption and the... (More)
 The force between two planar charged surfaces in the presence of polyampholytes (PAs) is investigated as a function of the surface separation. The model system contains PA molecules with zero net charge adsorbing onto the charged surfaces from a dilute surrounding solution without salt. We compare the results obtained on three levels of approximation: (i) polyampholytes moving in the mean field due to the counterions, i.e., in the PoissonBoltzmann field, (ii) PAs in a selfconsistent field generated by both counterions and PA monomers, and (iii) with all interactions treated explicitly. Either the amount of PA is kept constant for varying slit widths or chemical equilibrium with a bulk solution is considered. The PA adsorption and the surface force are found to strongly depend on the charge sequence along the chain. That is, polyampholytes with alternating charges do not adsorb, and their effect on the force is similar to that of neutral polymers. For PAs with long blocks oppositelycharged to the surfaces, however, the adsorption is more favorable and the monomer distribution for these blocks resembles that of polyelectrolytes. The counterions are in this case efficiently displaced from the surfaces, which leads to a significant extension of the electric double layer. Thus, our main conclusion is that adsorbing polyampholytes always increase the double layer repulsion between planar charged surfaces, and, the major cause for this phenomenon is the counterion redistribution. Yet, PA chains are capable of establishing "bridges" at short surface separations, but the resulting attraction can only slightly reduce the repulsive net pressure. The simplest approximation (i) is in principle only valid in the limit of zero PA density. At a finite concentration, it is sufficient, though essential, to include a linear correction to the PoissonBoltzmann solution in order to accurately predict the interfacial force or the amount of PA in the slit at chemical equilibrium. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/331934
 author
 Broukhno, Andrei ^{LU} ; Khan, Malek O; Åkesson, Torbjörn ^{LU} and Jönsson, Bo ^{LU}
 organization
 publishing date
 2002
 type
 Contribution to journal
 publication status
 published
 subject
 in
 Langmuir
 volume
 18
 issue
 16
 pages
 6429  6436
 publisher
 The American Chemical Society
 external identifiers

 wos:000177224400070
 scopus:0037031449
 ISSN
 07437463
 DOI
 10.1021/la020094l
 language
 English
 LU publication?
 yes
 id
 0ba24892e73d443880032d2938afea9c (old id 331934)
 date added to LUP
 20070810 16:15:22
 date last changed
 20171210 03:41:37
@article{0ba24892e73d443880032d2938afea9c, abstract = {The force between two planar charged surfaces in the presence of polyampholytes (PAs) is investigated as a function of the surface separation. The model system contains PA molecules with zero net charge adsorbing onto the charged surfaces from a dilute surrounding solution without salt. We compare the results obtained on three levels of approximation: (i) polyampholytes moving in the mean field due to the counterions, i.e., in the PoissonBoltzmann field, (ii) PAs in a selfconsistent field generated by both counterions and PA monomers, and (iii) with all interactions treated explicitly. Either the amount of PA is kept constant for varying slit widths or chemical equilibrium with a bulk solution is considered. The PA adsorption and the surface force are found to strongly depend on the charge sequence along the chain. That is, polyampholytes with alternating charges do not adsorb, and their effect on the force is similar to that of neutral polymers. For PAs with long blocks oppositelycharged to the surfaces, however, the adsorption is more favorable and the monomer distribution for these blocks resembles that of polyelectrolytes. The counterions are in this case efficiently displaced from the surfaces, which leads to a significant extension of the electric double layer. Thus, our main conclusion is that adsorbing polyampholytes always increase the double layer repulsion between planar charged surfaces, and, the major cause for this phenomenon is the counterion redistribution. Yet, PA chains are capable of establishing "bridges" at short surface separations, but the resulting attraction can only slightly reduce the repulsive net pressure. The simplest approximation (i) is in principle only valid in the limit of zero PA density. At a finite concentration, it is sufficient, though essential, to include a linear correction to the PoissonBoltzmann solution in order to accurately predict the interfacial force or the amount of PA in the slit at chemical equilibrium.}, author = {Broukhno, Andrei and Khan, Malek O and Åkesson, Torbjörn and Jönsson, Bo}, issn = {07437463}, language = {eng}, number = {16}, pages = {64296436}, publisher = {The American Chemical Society}, series = {Langmuir}, title = {Polyampholyteinduced repulsion between charged surfaces: Monte Carlo simulation studies}, url = {http://dx.doi.org/10.1021/la020094l}, volume = {18}, year = {2002}, }