\”AFM\”: add PEG, conductive polymer to achieve self-healing!

A self-healing material sensitive to changes in the external environment, current sensing, and information processing in one drive, the mechanism of biological processes by simulating self-repairing damage in the event of damage over a material capable of spontaneous process or caused by an external input intelligent self-healing material. In the application of wearable electronic devices, due to mechanical movement or prolonged contact with living tissue and biological fluids may cause frequent damage, so these devices is particularly important in the application self-healing material. Wherein the polystyrene sulfonic acid doped conducting polymer poly (3,4-ethylenedioxy thiophene) (PEDOT: PSS) is widely used as self-healing material concerned. PEDOT: PSS film can be cut with a razor after repairing electricity through water, but wet PEDOT: PSS film is very fragile, after drying their self-healing behavior disappears. Although the surfactant Triton X-100 incorporated into the PEDOT: PSS having an autonomous self-repair ability, but Triton X-100 has the potential toxicity can not be used in biological field of electronics. Accordingly, it is necessary to explore new dopant to improve the PEDOT: PSS film performance. Based on this, the Institute of Montreal, Canada, Fabio Cicoira (author) team based on previous findings, the PEDOT: PSS film was added polyethylene glycol (PEG) may reduce the density of the stretched film cracks, thereby significantly It can improve the tensile properties of the organic electrochemical transistor. PEG is also known as PEDOT: PSS conductivity enhancer, is used to alter the mechanical properties of several polymers. Meanwhile, PEG having a good biocompatibility and antifouling property. Thus, they are explored from the PEDOT: PSS mixture of self-healing and PEG obtained in the film. The study found that the PEDOT: PSS during processing of the mixture of the aqueous suspension and PEG film is formed by sharp cutting blades, even in the presence of glycerol conductivity enhancers, also with reproducible autonomous self-repair property. By changing the amount of the film of the PEG, the molecular weight of PEG or PEG-containing thin film was dipped in methanol, can be self-healing function switches from the autonomous function is water. Furthermore, addition of PEG was also found that the Young\’s modulus decrease, and increase the PEDOT: PSS film elongation at break, thereby forming a soft viscoelastic material.

Photo [A]

Preliminary studies have found that adding at least 3% of PEG to PEDOT: PSS aqueous suspension can be displayed by the repair function. Thus, the authors focus on the PEDOT: PSS film and the obtained mixture of 4% PEG-400 in. From the PEDOT: PSS and a mixture of 4% PEG-400 (the thickness of about 15 μm, the conductivity of about 200 S cm-1) still showed autonomous self-repair after repeated cutting, healing rate of close to 100%. When adding 5 v / v% glycerol to the mixture, the same behavior is observed, and the conductivity was increased to 400 S cm-1. The process occurs rapidly, healing time ranging between 50-800 ms, independent observed cut width of between about 10-60 μm. When the cutting width increased to 100 μm, autonomous self-healing disappeared.

using thermogravimetric analysis (TGA) was found that contained 4 v / v% and sample 10 v / v% PEG-400 and 80% weight loss. Fourier Transform Infrared Spectroscopy (FTIR) spectra, 2875 cm-1 (CH stretching) and 1645 cm-1 (COH bending), and a peak 3300 cm-1 (OH stretching) of the film was confirmed broad band of PEG. With the increase of the content of PEG in 2875 and increasing the peak intensity at intensity broadband and 1645 cm-1, indicating that the other hydroxyl group of PEG PEG molecules form hydrogen bonds, and with a PEDOT: PSS sulfonate group group. By the original PEDOT: PSS solution containing different concentrations of PEG-400 PEDOT: PSS solution processing of PEDOT: PSS film subjected to a tensile stress strain measurements and dynamic mechanical analysis (DMA), found that stress-strain response of the film show all almost linear behavior. With the increase in PEG content, the Young\’s modulus decreases, the elongation at break. Wherein, added 4 v / v% of PEG-400, having a stress-strain response of 1.5 MPa, elongation at break 8.5% increase in electrical conductivity of 200 S cm-1, the most balanced.

The results PSS and varying amounts of PEG-400 showed that by increasing the amount of PEG, PEDOT: PSS and viscoelastic flexible film with Independent self-healing, but further research is needed to establish the mechanical properties of the clear link between the self-repair behavior. A film made from a mixture containing 4% PEG having significant flexibility and viscoelasticity can be displayed autonomous self-repair capability. However, a reduced amount of PEG to 1% of the original cause PEDOT: PSS mechanical properties similar to, and independent of the water from the healing-induced change healing. Performing the methanol soaking, the conductivity increases to 200 S cm-1 1400 S cm-1. Further, PEDOT PEG containing: PSS film self-repairing property also depends on the molecular weight of the PEG. Studied by adding PEG-200, PEG-1500, PEO-100000, and the amount of PEO-5000000 was kept constant at 4 v / v%, wherein the film containing only PEG-200 exhibited autonomous healing, conductivity and PEG-400 similar. While others are self-healing efficiency declined, because longer chain PEG having a molecular weight lower mobility, it may lead to increased rigidity, thus preventing damage to the material back into the region after cutting.

To further study the healing process, the researchers used has an inverted optical microscope of the cutting / healing process carried out in situ imaging. Imaging display cutting process, as the blade moves forward, the gap resulting from the cleavage becomes narrower. After cutting imaged immediately found the gap had completely healed and invisible. These results suggest that, immediately after cutting, material can quickly flow back into the damaged area, which may be due to the viscoelastic properties of PEG given. Present in the film of PEG chains by forming hydrogen bonds with PSS shield ionic interactions between the PEDOT and PSS, so that the phase separation between the PEDOT and PSS, PEDOT domain and facilitate the formation of aggregates, thereby increasing the conductivity of the film . In addition, PEG chain also as PEDOT: PSS soft substrate particle, and the hydrophilic chain PSSProvide adequate mixing between the solid and entangled, thus facilitating the material after cutting back to the damaged area.

Link: https://onlinelibrary.wiley.com/doi/full/ 10.1002 / adfm.202002853