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Equilibrium aspects of polycation adsorption on silica surface: How the adsorbed layer responds to changes in bulk solution

Samoshina, Yulia LU ; Nylander, Tommy LU ; Shubin, V; Bauer, R and Eskilsson, K (2005) In Langmuir 21(13). p.5872-5881
Abstract
Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M-w is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount F of CPAM increases with pH for all studied electrolyte concentrations until a plateau F is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount.... (More)
Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M-w is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount F of CPAM increases with pH for all studied electrolyte concentrations until a plateau F is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount. The thickness of adsorbed polymer layers, obtained by ellipsometry, increases with electrolyte concentration and decreases with pH. At low c(s) and high pH the polyelectrolyte adsorbs in a flat conformation. An overcompensation of the surface charge (charge reversal) by the adsorbed polyelectrolyte is observed at high c, and low pH. To reveal the reversibility of the polyelectrolyte adsorption with respect to the adsorbed amount and layer thickness, parameters such as polyelectrolyte concentration (cp), c(s) and pH were changed during the experiment. Generally, similar adsorbed layer properties were obtained independent of whether adsorption was obtained directly to initially bare surface or by changing pH, c(s) or the concentration of polyelectrolyte solution in the presence of a preadsorbed layer, provided that the coverage of the preadsorbed layer was low. Once a steady state of the measured parameters (Gamma, d) was reached, experimental conditions were restored to the original values and corresponding changes in Gamma and adsorbed layer thickness were recorded. For initially low surface coverage it was impossible to restore the layer properties, and in this case we always ended up with higher coverage than the initial values. For initial high surface coverage it was usually possible to restore the initial layer properties. Thus, we concluded that polyelectrolyte appears only partially reversible to changes in the solution conditions due the slow rearrangement process within the adsorbed layer. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
21
issue
13
pages
5872 - 5881
publisher
The American Chemical Society
external identifiers
  • wos:000229886300037
  • pmid:15952836
  • scopus:21644490349
ISSN
0743-7463
DOI
10.1021/la050069q
language
English
LU publication?
yes
id
fe304d0e-404e-40ee-944c-ef647966ea9c (old id 157583)
date added to LUP
2007-07-12 10:59:13
date last changed
2017-06-18 03:37:56
@article{fe304d0e-404e-40ee-944c-ef647966ea9c,
  abstract     = {Adsorption of cationic high molecular weight polyacrylamides (CPAM) (M-w is about 800 kDa) with different fractions of cationic units tau = 0.09 and tau = 0.018 onto silica surface was studied over a wide range of pH (4-9) and KCl concentration (c(s) = 10(-3)-10(-1) M) by in-situ null ellipsometry. We discuss how the adsorbed layer depends on the bulk conditions as well as kinetically responds to changes in solution conditions. The adsorbed amount F of CPAM increases with pH for all studied electrolyte concentrations until a plateau F is reached at pH > 6. At low pH we observed an increase in adsorbed amount with electrolyte concentration. At high pH there is no remarkable influence of added salt on the values of the adsorbed amount. The thickness of adsorbed polymer layers, obtained by ellipsometry, increases with electrolyte concentration and decreases with pH. At low c(s) and high pH the polyelectrolyte adsorbs in a flat conformation. An overcompensation of the surface charge (charge reversal) by the adsorbed polyelectrolyte is observed at high c, and low pH. To reveal the reversibility of the polyelectrolyte adsorption with respect to the adsorbed amount and layer thickness, parameters such as polyelectrolyte concentration (cp), c(s) and pH were changed during the experiment. Generally, similar adsorbed layer properties were obtained independent of whether adsorption was obtained directly to initially bare surface or by changing pH, c(s) or the concentration of polyelectrolyte solution in the presence of a preadsorbed layer, provided that the coverage of the preadsorbed layer was low. Once a steady state of the measured parameters (Gamma, d) was reached, experimental conditions were restored to the original values and corresponding changes in Gamma and adsorbed layer thickness were recorded. For initially low surface coverage it was impossible to restore the layer properties, and in this case we always ended up with higher coverage than the initial values. For initial high surface coverage it was usually possible to restore the initial layer properties. Thus, we concluded that polyelectrolyte appears only partially reversible to changes in the solution conditions due the slow rearrangement process within the adsorbed layer.},
  author       = {Samoshina, Yulia and Nylander, Tommy and Shubin, V and Bauer, R and Eskilsson, K},
  issn         = {0743-7463},
  language     = {eng},
  number       = {13},
  pages        = {5872--5881},
  publisher    = {The American Chemical Society},
  series       = {Langmuir},
  title        = {Equilibrium aspects of polycation adsorption on silica surface: How the adsorbed layer responds to changes in bulk solution},
  url          = {http://dx.doi.org/10.1021/la050069q},
  volume       = {21},
  year         = {2005},
}