Organization of Self-Assembled Peptide−Polymer Nanofibers in Solution

The solution structure and the aggregation behavior of stiff polymer−peptide nanofibers, self-assembled from well-defined poly(ethylene oxide)−peptide conjugates are described. Aqueous solutions at different concentrations of core−shell nanofibers were investigated by cryo-fixation transmission electron microscopy (cryoTEM) and small-angle neutron scattering (SANS). Both methods show the presence of stiff, extended nanofibers in dilute solution, providing nanodimensions for the fiber cross section, which are in good agreement with previously shown investigations on dried and deposited fibers. Moreover the previously suggested core−shell character of the fiber cross section could be verified by SANS density profiles. In concentrated solutions exceeding 2 mg/mL, the nanofibers tended to further organize into nematic “bundles”. Polarized optical microscopy (POM) indeed shows birefringence of the solutions and typical Schlieren textures in shear oriented films, consistent with high aspect ratio nanofibers. The results of this investigation are discussed in the context of the Flory theory of rigid rods.