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Conformation change induces agregation

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Pluronic F127 are neutral tri-block copolymers forming micelles that are largely studied for drug delivery. We observed the structures and organization of the micelles in presence of a natural polyelectrolyte having important biological functions, the hyaluronic acid in semi-dilute regime, as a function of the nature and concentration of added salt by differential scanning calorimetry and small angle neutron scattering.

Hyaluronic acid reduces the critical micellar temperature to the same extend as an increase of the ionic strength. Within the investigated HA concentration range, the size and shape of the micelles are not modified by the addition of HA but their dispersion state depends on the added salt concentration. By increasing the ionic strength, we observed the formation of small micellar clusters which organize into a face-centered cubic liquid crystalline phase at high salt concentration. This behavior is reinforced by increasing the HA concentration or the molecular weight of the polyelectrolyte chains. The nature of the salt plays also a role and divalent cations such as Ca2+ promote the clustering of micelles and their crystallization. The origin of the aggregative behavior is the change of the HA chain conformation - from stretched to coil- and the screening of the electrostatic forces by addition of salt, effects which in turn induces an excluded volume around the micelles and exerts a depletion interaction.

This work published in JCIS has been largely initiated and realized by Isabelle Grillo from Institut Laue Langevin, recently deceased. Their colleagues and friends Jérôme Combet (ICS, Strasbourg and a time visitor at the Liphy) and Isabelle Morfin wish to address here their fond acknowledgement to Isabelle.

Voir en ligne : I.Grillo, I.Morfin, J.Combet, Journal of Colloid and Interface Science