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Critical salt effects in the swelling behavior of a weak polybasic brush

Willott, Joshua D ; Murdoch, Timothy J ; Humphreys, Ben A LU ; Edmondson, Steve ; Webber, Grant B and Wanless, Erica J (2014) In Langmuir 30(7). p.1827-1836
Abstract
The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA)
brushes in response to changes in solution pH and ionic strength has
been investigated. The brushes were synthesized by ARGET ATRP
methodology at the silica–aqueous solution interface via two different
surface-bound initiator approaches: electrostatically adsorbed cationic
macroinitiator and covalently anchored silane-based ATRP initiator
moieties. The pH-response of these brushes is studied as a function of
the solvated brush thickness in a constant flow regime that elucidates
the intrinsic behavior of polymer brushes. In situ ellipsometry
equilibrium measurements show the pH-induced brush swelling and collapse
... (More)
The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA)
brushes in response to changes in solution pH and ionic strength has
been investigated. The brushes were synthesized by ARGET ATRP
methodology at the silica–aqueous solution interface via two different
surface-bound initiator approaches: electrostatically adsorbed cationic
macroinitiator and covalently anchored silane-based ATRP initiator
moieties. The pH-response of these brushes is studied as a function of
the solvated brush thickness in a constant flow regime that elucidates
the intrinsic behavior of polymer brushes. In situ ellipsometry
equilibrium measurements show the pH-induced brush swelling and collapse
transitions are hysteretic in nature. Furthermore, high temporal
resolution kinetic studies demonstrate that protonation and solvent
ingress during swelling occur much faster than the brush charge
neutralization and solvent expulsion during collapse. This hysteresis is
attributed to the formation of a dense outer region or skin during
collapse that retards solvent egress. Moreover, at a constant pH below
its pKa, the PDEA brush exhibited a critical
conformational change in the range 0.5–1 mM electrolyte, a range much
narrower than predicted by the theory of the osmotic brush regime. This
behavior is attributed to the hydrophobicity of the collapsed brush. The
swelling and collapse kinetics for this salt-induced transition are
nearly identical. This is in contrast to the asymmetry in the rate of
the pH-induced response, suggesting an alternative mechanism for the two
processes dependent on the nature of the environmental trigger. (Less)
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publishing date
type
Contribution to journal
publication status
published
subject
in
Langmuir
volume
30
issue
7
pages
10 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:84894647016
ISSN
0743-7463
DOI
10.1021/la4047275
language
English
LU publication?
no
id
112f0da1-1f68-4be9-bc65-3d67cedaa08a
date added to LUP
2022-04-01 21:11:51
date last changed
2022-07-02 04:03:54
@article{112f0da1-1f68-4be9-bc65-3d67cedaa08a,
  abstract     = {{The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA)<br>
 brushes in response to changes in solution pH and ionic strength has <br>
been investigated. The brushes were synthesized by ARGET ATRP <br>
methodology at the silica–aqueous solution interface via two different <br>
surface-bound initiator approaches: electrostatically adsorbed cationic <br>
macroinitiator and covalently anchored silane-based ATRP initiator <br>
moieties. The pH-response of these brushes is studied as a function of <br>
the solvated brush thickness in a constant flow regime that elucidates <br>
the intrinsic behavior of polymer brushes. <i>In situ</i> ellipsometry <br>
equilibrium measurements show the pH-induced brush swelling and collapse<br>
 transitions are hysteretic in nature. Furthermore, high temporal <br>
resolution kinetic studies demonstrate that protonation and solvent <br>
ingress during swelling occur much faster than the brush charge <br>
neutralization and solvent expulsion during collapse. This hysteresis is<br>
 attributed to the formation of a dense outer region or skin during <br>
collapse that retards solvent egress. Moreover, at a constant pH below <br>
its p<i>K</i><sub>a</sub>, the PDEA brush exhibited a critical <br>
conformational change in the range 0.5–1 mM electrolyte, a range much <br>
narrower than predicted by the theory of the osmotic brush regime. This <br>
behavior is attributed to the hydrophobicity of the collapsed brush. The<br>
 swelling and collapse kinetics for this salt-induced transition are <br>
nearly identical. This is in contrast to the asymmetry in the rate of <br>
the pH-induced response, suggesting an alternative mechanism for the two<br>
 processes dependent on the nature of the environmental trigger.}},
  author       = {{Willott, Joshua D and Murdoch, Timothy J and Humphreys, Ben A and Edmondson, Steve and Webber, Grant B and Wanless, Erica J}},
  issn         = {{0743-7463}},
  language     = {{eng}},
  number       = {{7}},
  pages        = {{1827--1836}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Langmuir}},
  title        = {{Critical salt effects in the swelling behavior of a weak polybasic brush}},
  url          = {{http://dx.doi.org/10.1021/la4047275}},
  doi          = {{10.1021/la4047275}},
  volume       = {{30}},
  year         = {{2014}},
}