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Theoretical Predictions of Temperature-Induced Gelation in Aqueous Dispersions Containing PEO-Grafted Particles

Xie, Fei LU ; Woodward, Clifford E. and Forsman, Jan LU (2016) In The Journal of Physical Chemistry Part B 120(16). p.3969-3977
Abstract

In this work, we utilize classical polymer density functional theory (DFT) to study gelation in systems containing colloidal particles onto which polymers are grafted. The solution conditions are such that the corresponding bulk system displays a lower critical solution temperature (LCST). We specifically compare our predictions with experimental results by Shay et al. (J. Rheol. 2001, 45, 913-927), who investigated temperature response in aqueous dispersions containing polystyrene particles (PS), with grafted 45-mer poly(ethylene oxide) (PEO) chains. Our DFT treatment is based on a model for aqueous PEO solutions that was originally developed by Karlström for bulk solutions. In this model, monomers are assumed to be in either of two... (More)

In this work, we utilize classical polymer density functional theory (DFT) to study gelation in systems containing colloidal particles onto which polymers are grafted. The solution conditions are such that the corresponding bulk system displays a lower critical solution temperature (LCST). We specifically compare our predictions with experimental results by Shay et al. (J. Rheol. 2001, 45, 913-927), who investigated temperature response in aqueous dispersions containing polystyrene particles (PS), with grafted 45-mer poly(ethylene oxide) (PEO) chains. Our DFT treatment is based on a model for aqueous PEO solutions that was originally developed by Karlström for bulk solutions. In this model, monomers are assumed to be in either of two classes of states, labeled A and B, where B is more solvophobic than A. On the other hand, the degeneracy of B exceeds that of A, causing the population of solvophobic monomers to increase with temperature. In agreement with experimental findings by Shay et al., we locate gelation at temperatures considerably below Tθ, and far below the LCST for such chain lengths. This gelation occurs also without any dispersion interactions between the PS particles. Interestingly, the polymer-induced interaction free energy displays a nonmonotonic dependence on the grafting density. At high grafting densities, bridging attractions between grafted layers take place (considerably below Tθ). At low grafting densities, on the other hand, the polymers are able to bridge across to the other particle surface. Shay et al. conducted their experiments at very low ionic strength, using deionized water as a solvent. We demonstrate that even minute amounts of adsorbed charge on the surface of the particles, can lead to dramatic changes of the gelation temperature, especially at high grafting densities. Another interesting prediction is the existence of elongated (chainlike) equilibrium structures, at low particle concentrations. We emphasize that our model does not rely upon any temperature-dependent interactions.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
The Journal of Physical Chemistry Part B
volume
120
issue
16
pages
9 pages
publisher
The American Chemical Society
external identifiers
  • scopus:84968791819
  • wos:000375521600020
ISSN
1520-6106
DOI
10.1021/acs.jpcb.6b01419
language
English
LU publication?
yes
id
ced2ad0a-27d6-46f5-bad6-a8fea8ff66c0
date added to LUP
2016-07-26 08:33:40
date last changed
2017-07-05 17:27:45
@article{ced2ad0a-27d6-46f5-bad6-a8fea8ff66c0,
  abstract     = {<p>In this work, we utilize classical polymer density functional theory (DFT) to study gelation in systems containing colloidal particles onto which polymers are grafted. The solution conditions are such that the corresponding bulk system displays a lower critical solution temperature (LCST). We specifically compare our predictions with experimental results by Shay et al. (J. Rheol. 2001, 45, 913-927), who investigated temperature response in aqueous dispersions containing polystyrene particles (PS), with grafted 45-mer poly(ethylene oxide) (PEO) chains. Our DFT treatment is based on a model for aqueous PEO solutions that was originally developed by Karlström for bulk solutions. In this model, monomers are assumed to be in either of two classes of states, labeled A and B, where B is more solvophobic than A. On the other hand, the degeneracy of B exceeds that of A, causing the population of solvophobic monomers to increase with temperature. In agreement with experimental findings by Shay et al., we locate gelation at temperatures considerably below T<sub>θ</sub>, and far below the LCST for such chain lengths. This gelation occurs also without any dispersion interactions between the PS particles. Interestingly, the polymer-induced interaction free energy displays a nonmonotonic dependence on the grafting density. At high grafting densities, bridging attractions between grafted layers take place (considerably below T<sub>θ</sub>). At low grafting densities, on the other hand, the polymers are able to bridge across to the other particle surface. Shay et al. conducted their experiments at very low ionic strength, using deionized water as a solvent. We demonstrate that even minute amounts of adsorbed charge on the surface of the particles, can lead to dramatic changes of the gelation temperature, especially at high grafting densities. Another interesting prediction is the existence of elongated (chainlike) equilibrium structures, at low particle concentrations. We emphasize that our model does not rely upon any temperature-dependent interactions.</p>},
  author       = {Xie, Fei and Woodward, Clifford E. and Forsman, Jan},
  issn         = {1520-6106},
  language     = {eng},
  month        = {04},
  number       = {16},
  pages        = {3969--3977},
  publisher    = {The American Chemical Society},
  series       = {The Journal of Physical Chemistry Part B},
  title        = {Theoretical Predictions of Temperature-Induced Gelation in Aqueous Dispersions Containing PEO-Grafted Particles},
  url          = {http://dx.doi.org/10.1021/acs.jpcb.6b01419},
  volume       = {120},
  year         = {2016},
}