Modulating hierarchical self-assembly behavior of a peptide amphiphile/nonionic surfactant mixed system

Abstract

The self-assembly behavior of a nonionic surfactant (n-dodecyl tetraethylene monoether, C₁₂E₄) and a peptide amphiphile (PA, C₁₆-GK-3) mixed system was investigated using a combination of microscopic, scattering and spectroscopic techniques, including transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), polarized optical microscopy (POM) observations, small-angle X-ray scattering (SAXS), Fourier transform infrared (FT-IR) spectroscopy, circular dichroism (CD) and rheological measurements. The change of the contents of C₁₆-GK-3 and C₁₂E₄ induced the transitions in the nanostructures and simultaneously led to changes in macroscopic properties, i.e., mixtures of C₁₂E₄ with C₁₆-GK-3 can be hierarchically self-assembled into various helical nanofibers and then further assembled to dandelion-like and dendrite nanostructures by changing the content of C₁₆-GK-3 and C₁₂E₄, which resulted in transitions from solution to two phase, sol and hydrogel states that were noted on increasing the concentration of C₁₆-GK-3 at a fixed concentration of C₁₂E₄ or varying C₁₂E₄ concentration at a fixed concentration of C₁₆-GK-3. On the basis of a series of characterizations, we proposed a possible mechanism of the self-assembly, for which the hydrogen bonding interaction between the headgroups of C₁₆-GK-3 and between C₁₆-GK-3 and C₁₂E₄, as well as hydrophobic interaction between the alkyl chains of C₁₆-GK-3 and C₁₂E₄, were the main driving forces.