A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod-shaped and later exhibited three-dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide-angle X-ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay.
A biocompatible,
flexible, yet robust conductive composite hydrogel
(CCH) for wearable pressure/strain sensors has been achieved by an
all-solution-based approach. The CCH is rationally constructed by
in situ polymerization of aniline (An) monomers in the polyvinyl alcohol
(PVA) matrix, followed by the cross-linking of PVA with glutaraldehyde
(GA) as the cross-linker. The unique multiple synergetic networks
in the CCH including strong chemical covalent bonds and abundance
of weak physical cross-links, i.e., hydrogen bondings and electrostatic
interactions, impart excellent mechanical strength (a fracture tensile
strength of 1200 kPa), superior compressibility (ε = 80%@400
kPa), outstanding stretchability (a fracture strain of 670%), high
sensitivity (0.62 kPa–1 at a pressure range of 0–1.0
kPa for pressure sensing and a gauge factor of 3.4 at a strain range
of 0–300% for strain sensing, respectively), and prominent
fatigue resistance (1500 cycling). As the flexible wearable sensor,
the CCH is able to monitor different types of human motion and diagnostically
distinguish speaking. As a proof of concept, a sensing device has
been designed for the real-time detection of 2D distribution of weight
or pressure, suggesting its promising potentials for electronic skin,
human–machine interaction, and soft robot applications.
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