| Solvent quality affects the interactions between neutral polymer brushes and colloids as manifested in the concentration profiles of the colloidal particles, cprt(z), and the corresponding adsorption isotherms. Lowering the solvent quality, and eventual brush collapse, reduce the osmotic pressure at height z within the brush, Π(z), and with it the associated free energy penalty of inserting a particle into the brush, Fins(z). Brush collapse thusfavors penetration into the brush and adsorption within it, an effect utilized in tissue engineering, chromatography etc. In the self consistent field theory of brushes the effect reflects both the amplitude and form of Π(z). For good, &Thetao; and poor solvents, denoted by i = g, Θ, p, the Π(z) profile is Πi(z)=Πi(0)uimi(z/Hi) where Hi is the brush height and ui =1 − z2/Hi2. The analysis utilizes the known mg =2, mΘ =3/2 as well as the derived mp =1 together with Πp(0)/Πg(0) ∼ Hp/Hg and ΠΘ(0)/Πg(0) ∼ HΘ/Hg. Fins(z) ≈ Πi(z)R3 incurred by spherical particles of radius R ≪ Hi is significant for R>Rins(i) ∼ Πi(0)-1/3 where Rins(i) scales with the grafting density σ as σ−4/9, σ−1/2 and σ−2/3, respectively. For non-adsorbing particles with R≫Rins(i) the particles penetrate the brush to a depth of δi≈ Hi(Rins(i)/R)ri with ri =3/2, 2, 3, and δg >δΘ >δp. Primary adsorption at the wall due to wall-particle contact attraction energy E is repressed when R> (E/kBT)1/3Rins(i). Ternary adsorption due to weak monomer-particle attraction is driven by a free energy scaling as ϕ(z)R2 and thus stronger in poor solvents when the monomer volume fraction ϕ(z) is higher. Accordingly the associated cprt(z) is high for particles large enough to accumulate kBT or more of attractive monomer-particle contacts but small enough to avoid large Fins(z).
for LaTeX users @article{AHalperin2011-44,
author = {A. Halperin and M. Kr\"oger and E. B. Zhulina},
title = {Colloid-brush interactions: The effect of solvent quality},
journal = {Macromolecules},
volume = {44},
pages = {3622-3638},
year = {2011}
}
\bibitem{AHalperin2011-44} A. Halperin, M. Kr\"oger, E.B. Zhulina,
Colloid-brush interactions: The effect of solvent quality,
Macromolecules {\bf 44} (2011) 3622-3638.AHalperin2011-44
A. Halperin, M. Kr\"oger, E.B. Zhulina
Colloid-brush interactions: The effect of solvent quality
Macromolecules,44,2011,3622-3638 |
mk@mat.ethz.ch
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