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Etude expérimentale de polyélectrolytes hydrophobes modèles

Abstract : Hydrophobic polyelectrolytes are water-soluble polymers, carrying charged groups in water, which is a poor solvent for the backbone. For this thesis, we aimed to investigate experimentally the physical properties of well-defined model hydrophobic polyelectrolytes. For this purpose, we have synthesised a series of poly(styrene-co-styrenesulfonic acid, sodium salt), abbreviated PSS, of charge fractions $f$ ranging from 30\% to 100\% and containing from $N=120$ to $N=2520$ monomers per chain. Both bulk and interfacial properties have been investigated.\\ \emph(1. Bulk properties.) The effective charge fraction is anomalously reduced compared to that of hydrophilic polyelectrolytes. The structural properties have been investigated by small angle X-ray scattering and colloidal probe technique. We have found that the correlation length scales like $N^0C_p^(-\alpha)$, where $C_p$ is the polymer concentration and $\alpha$ a $f$ dependent exponent, ranging from $1/2$ when PSS is fully sulfonated to reach 1/3 close to the solubility limit. These observations are interpreted in the framework of a theoretical model predicting a pearl-necklace conformation for the single chain, composed of dense globules (the pearls) connected by elongated chain segments. Conversely, collective dynamics is almost independent of hydrophobicity. \emph(2. Bulk properties.) We have devised an experiment in order to trap the PSS chain by adsorption onto oppositely charged solid surfaces. The adsorbed PSS layer immersed in water has been characterised by various \emph(in situ) techniques : ellipsometry, high energy X-ray reflectivity and atomic force microscopy. We have found that the pearl size depends strongly on $f$. The pearl size, ranging from 1 to 5 nm, is in agreement with the predictions of the pearl-necklace theory. Hydrophobic polyelectrolytes adsord also spontaneously onto hydrophobic substrates, the pearls, in some cases, unfolding on the surface.
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Contributor : Damien Baigl <>
Submitted on : Wednesday, October 22, 2003 - 2:55:34 PM
Last modification on : Wednesday, September 23, 2020 - 4:32:40 AM
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  • HAL Id : tel-00003620, version 1

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Damien Baigl. Etude expérimentale de polyélectrolytes hydrophobes modèles. Biophysique [physics.bio-ph]. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00003620⟩

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