Recently, we have been interested in hydrophobic derivatives of polysaccharides such as chitosan and alginate. Such polymers have a hydrophilic and water-soluble backbone, with hydrophobic tails attached at random points along the backbone. The hydrophobic groups enable the polymer to interact strongly with nanoscale self-assembled structures such as micelles and vesicles. In particular, hydrophobically modified chitosan (hmC) has been shown to convert a solution of vesicles into an elastic gel. Gelation is attributed to the insertion of hydrophobes from hmC chains into the bilayers of vesicles; thereby the polymer bridges the vesicles into a three-dimensional network. Similar gelation has also been shown to occur with biological cells, including blood. In this study, we further probe the rheology and nanostructure of vesicle/hmC mixtures. We are particularly interested in the effect of hydrophobe tail length and graft density. Hydrophobic alkyl tails of length varying from C6 to C18 are attached to the backbone of hmC. The graft density of hydrophobes is varied from about 2 to 10 mol% (relative to the fraction of free amines on the chitosan). As a model system of vesicles, we use mixed surfactant (catanionic) vesicles formed by combining the cationic surfactant cetyl trimethylammonium tosylate (CTAT) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS). We will present data from dynamic and steady-shear rheology as well as from small-angle neutron scattering on vesicle-hmC mixtures. Physical insights based on these data will be discussed in the presentation.

Gelation of vesicles by hydrophobically modified biopolymers: Effect of hydrophobe length and graft density

246th National Meeting (2013)

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