From Dielectric to\nElectro-Responsive Thermoplastics:\nAn Approach Based on Electro-Thermal Reorientation and Charged Gas\nActivation

The transition from insulator to electro-responsive has\nbeen successfully\nachieved by earlier studies for some inorganic materials by applying\nexternal stimuli that modify their 3D and/or electronic structures.\nIn the case of insulating polymers, this transition is frequently\naccomplished by mixing them with other electroactive materials, even\nthough a few physical treatments that induce suitable chemical modifications\nhave also been reported. In this work, a smart approach based on the\napplication of an electro-thermal reorientation process followed by\na charged gas activation treatment has been developed for transforming\ninsulating 3D printed polymers into electro-responsive materials.\nFirst, the developed procedure has been exhaustively investigated\nfor 3D printed poly(lactic acid) (PLA) and subsequently has been extended\nto 3D printed polypropylene (PP) and poly(ethylene terephthalate glycol)\n(PETG) specimens. FTIR and Raman spectroscopies, X-ray diffraction,\nX-ray photoelectron spectroscopy, scanning electron microscopy, and\nwater contact angle measurements confirmed that, while the electro-thermal\nreorientation mainly promotes the crystallinity of the samples, the\ncharged gas activation oxidizes the C–O bonds at the surface\nand consequently modifies the surface morphology and wettability.\nFurthermore, cyclic voltammetry assays demonstrated that treated PLA,\nPP, and PETG are electro-responsive, even though the electrochemical\nactivity was much higher for oxygen-containing polymers (PLA and PETG)\nthan for the oxygen-free one (PP). Finally, as a proof of concept,\ntreated 3D printed PLA specimens have been used as electrochemical\nsensors to detect dopamine (DA), an important neurotransmitter, in\na concentration interval ranging from 50 to 1000 μM. The peak\nassociated with the oxidation from DA to dopaminoquinone and the linearity\nof the calibration plot, which was constructed using the anodic peak\ncurrent, proved that treated PLA is not only electro-responsive but\nalso able to electrocatalyze the oxidation of DA.