Dodecyl Surfactants Induced Crystalline Modifications in Polyamide-6 Nanofibers

Herein, we present the first results of how the addition of dodecyl surfactants having three different polar groups viz., phenol (−C6H5OH), carboxylic acid (−COOH), and benzenesulfonic acid (−C6H5SO3H) to polyamide-6 (PA6) transforms its crystalline phase from γ to α-form upon the formation of nanofibers. Interestingly, each of these surfactant-incorporated nanofibers leads to the orientation of the resultant monoclinic α-crystalline form in a preferred plane. The surfactant-induced change in orientations is also realized using PA6 films obtained by solvent casting. A direct correlation has been found between viscosity and ionic conductivity in the solution phase, which is distinct from their generally known inverse relation. The conversion from the γ- to α-form of PA6 nanofibers is ascertained by X-ray diffraction and is supplemented by Fourier transform infrared results. The scanning electron microscopy images revealed that the incorporation of surfactants reduced the nanofiber diameter. The present study allowed us to suggest that the modification of PA6 nanofibers using surfactants of different hydrogen bonding abilities can lead to the preferential planar orientation of α-crystalline forms (edge-on and/or flat-on), revealing that surfactants can act as shape-directing agents even in nanofibers. We expect that the obtained results will be of use in the study of many biological systems that have amide/peptide linkages and exhibit nanofilamentary architectures.