Highly Stretchable Stress-Strain Sensor from Elastomer Nanocomposites with Movable Cross-links and Ketjenblack.

Practical applications like very thin stress-strain sensors require high strength, stretchability, and conductivity, simultaneously. One of the approaches is improving the toughness of the stress-strain sensing materials. Polymeric materials with movable cross-links in which the polymer chain penetrates the cavity of cyclodextrin (CD) demonstrate enhanced strength and stretchability, simultaneously. We designed two approaches that utilize elastomer nanocomposites with movable cross-links and carbon filler (ketjenblack, KB). One approach is mixing SC (a single movable cross-network material), a linear polymer (poly(ethyl acrylate), PEA), and KB to obtain their composite. The electrical resistance increases proportionally with tensile strain, leading to the application of this composite as a stress-strain sensor. The responses of this material are stable for over 100 loading and unloading cycles. The other approach is a composite made with KB and a movable cross-network elastomer for knitting dissimilar polymers (KP), where movable cross-links connect the CD-modified polystyrene (PSCD) and PEA. The obtained composite acts as a highly sensitive stress-strain sensor that exhibits an exponential increase in resistance with increasing tensile strain due to the polymer dethreading from the CD rings. The designed preparations of highly repeatable or highly responsive stress-strain sensors with good mechanical properties can help broaden their application in electrical devices.

Synergetic improvement in the mechanical properties of polyurethanes with movable crosslinking and hydrogen bonds.

Polyurethane (PU) materials with movable crosslinking were prepared by a typical two-step synthetic process using an acetylated γ-cyclodextrin (TAcγCD) diol compound. The soft segment of PU is polytetrahydrofuran (PTHF), and the hard segment consists of hexamethylene diisocyanate (HDI) and 1,3-propylene glycol (POD). The synthesized PU materials exhibited the typical mechanical characteristics of a movable crosslinking network, and the presence of hydrogen bonds from the urethane bonds resulted in a synergistic effect. Two kinds of noncovalent bond crosslinking increased the Young's modulus of the material without affecting its toughness. Fourier transform infrared spectroscopy and X-ray scattering measurements were performed to analyze the effect of introducing movable crosslinking on the internal hydrogen bond and the microphase separation structure of PU, and the results showed that the carbonyl groups on TAcγCD could form hydrogen bonds with the PU chains and that the introduction of movable crosslinking weakened the hydrogen bonds between the hard segments of PU. When stretched, the movable crosslinking of the PU materials suppressed the orientation of polymer chains (shish-kebab orientation) in the tensile direction. The mechanical properties of the movable crosslinked PU materials show promise for future application in the industrial field.