Conducting Electrospun Poly(3-hexylthiophene-2,5-diyl) Nanofibers: New Strategies for Effective Chemical Doping and its Assessment Using Infrared Spectroscopy

Vibrational spectroscopy allows the investigation of structural properties of pristine and doped poly(3-hexylthiophene-2,5-diyl) (P3HT) in highly anisotropic materials, such as electrospun micro- and nanofibers. Here, we compare several approaches for doping P3HT fibers. We have selected two different electron acceptor molecules as dopants, namely iodine and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). In the case of iodine, we have explored the doping of the fibers according to several different procedures, i.e., by sequential doping both in vapors and in solution, and with a novel promising one-step method, which exploits the mixing of the dopant to the electrospinning feed solution. Polarized infrared (IR) spectroscopy experiments prove the orientation of P3HT chains, with the polymer backbone mainly running parallel to the fiber axis. After doping, P3HT fibers show very strong and polarized doping-induced IR active vibrations (IRAVs), which are the spectroscopic signature of the structure relaxation induced by the charged defects (polarons), thus providing an unambiguous proof of the effective doping. Raman spectroscopy complements the IR evidence: The Raman spectrum shows a clearly recognizable shift of the main band, the so-called effective conjugation coordinate band, in the doped samples. A simple protocol, which quantifies the evolution of the IRAV bands with time, allows monitoring of the doping stability over time and confirms that F4TCNQ is by far superior to iodine.

Conducting Electrospun Nanofibres: Monitoring of Iodine Doping of P3HT through Infrared (IRAV) and Raman (RaAV) Polaron Spectroscopic Features

Aligned polymer nanofibres are prepared by means of the electrospinning of a chlorobenzene solution containing regioregular poly(3-hexyltiophene-2,5-diyl), P3HT, and poly(ethylene oxide), PEO. The PEO scaffold is easily dissolved with acetonitrile, leaving pure P3HT fibres, which do not show structural modification. Polymer fibres, either with or without the PEO supporting polymer, are effectively doped by exposure to iodine vapours. Doping is monitored following the changes in the doping-induced vibrational bands (IRAVs) observed in the infrared spectra and by means of Raman spectroscopy. Molecular orientation inside the fibres has been assessed by means of IR experiments in polarised light, clearly demonstrating that electrospinning induces the orientation of the polymer chains along the fibre axis as well as of the defects introduced by doping. This work illustrates a case study that contributes to the fundamental knowledge of the vibrational properties of the doping-induced defects-charged polarons-of P3HT. Moreover, it provides experimental protocols for a thorough spectroscopic characterisation of the P3HT nanofibres, and of doped conjugated polymers in general, opening the way for the control of the material structure when the doped polymer is confined in a one-dimensional architecture.

Structural lipid nanoparticles self-assembled from electrospun core–shell polymeric nanocomposites

Electrospun core–sheath composite nanofibers are exploited as templates to manipulate molecular self-assembly for generating core–shell lipid nanoparticles.