Structural and Rheological Properties of Aqueous Viscoelastic Solutions and Gels of Tripodal Cholamide-Based Self-Assembled Supramolecules

Terech, Pierre and Maitra, Uday (2008) Structural and Rheological Properties of Aqueous Viscoelastic Solutions and Gels of Tripodal Cholamide-Based Self-Assembled Supramolecules. In: Journal of Physical Chemsitry B, 112 (43). pp. 13483-13492.

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Abstract

A tripodal cholic steroid (TCS+) derivative forms, hydrogels in acidic conditions that are studied by the small-angle neutron scattering and rheometry techniques. The self-assembled systems exhibit particular scattering and flow properties unusual in the class of molecular gels. The scattering data show separated form- and structure-factor features with, respectively, a low-Q correlation peak and a large-Q secondary oscillation. A probable aggregation model is deduced involving 3 TCS+ molecules per cross-section of fibrillar aggregates packed in a tail-to-tail fashion. The fibers have monodisperse cross-sections (40 angstrom diameter) and result from a versatile mechanism taking advantage of the free articulation of the three hydrophobic steroid pods (''umbrella-like'' packing) around the N+ charge. The N+ charges are distributed at the periphery of the cylinders and give rise to a moderate linear charge density (v similar to 0. 16 e/angstrom). The variation with concentration of the static scattering structure factor peak S(Q) reveals ordering properties typical of Id polyelectrolytes. The fibers further organize into fractal clusters characterized by their scattering signature at low-Q and also by the exponent of the scaling of the elastic shear modulus with the concentration. It is suggested that the TCS+ polyion fibers extend under shear (or in a concentrated environment) by varying the angle between the pods along the fiber axis. Viscosity overshoots appear at the startup of shear flow experiments. Analogies with the phenomenology observed with DNA solutions are discussed.

Item Type:	Journal Article
Publication:	Journal of Physical Chemsitry B
Publisher:	American Chemical Society
Additional Information:	Copyright of this article belongs to American Chemical Society.
Department/Centre:	Division of Chemical Sciences > Organic Chemistry
Date Deposited:	19 May 2009 05:43
Last Modified:	19 Sep 2010 04:53
URI:	http://eprints.iisc.ac.in/id/eprint/16762

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