Dodecyl Surfactants Induced Crystalline Modifications\nin Polyamide‑6 Nanofibers

Herein, we present the first results\nof how the addition of dodecyl\nsurfactants having three different polar groups viz., phenol (−C<sub>6</sub>H<sub>5</sub>OH), carboxylic acid (−COOH), and benzenesulfonic\nacid (−C<sub>6</sub>H<sub>5</sub>SO<sub>3</sub>H) to polyamide-6\n(PA6) transforms its crystalline phase from γ to α-form\nupon the formation of nanofibers. Interestingly, each of these surfactant-incorporated\nnanofibers leads to the orientation of the resultant monoclinic α-crystalline\nform in a preferred plane. The surfactant-induced change in orientations\nis also realized using PA6 films obtained by solvent casting. A direct\ncorrelation has been found between viscosity and ionic conductivity\nin the solution phase, which is distinct from their generally known\ninverse relation. The conversion from the γ- to α-form\nof PA6 nanofibers is ascertained by X-ray diffraction and is supplemented\nby Fourier transform infrared results. The scanning electron microscopy\nimages revealed that the incorporation of surfactants reduced the\nnanofiber diameter. The present study allowed us to suggest that the\nmodification of PA6 nanofibers using surfactants of different hydrogen\nbonding abilities can lead to the preferential planar orientation\nof α-crystalline forms (<i>edge-on</i> and/or <i>flat-on</i>), revealing that surfactants can act as shape-directing\nagents even in nanofibers. We expect that the obtained results will\nbe of use in the study of many biological systems that have amide/peptide\nlinkages and exhibit nanofilamentary architectures.