Electrical tree properties of grafted polypropylene studied by electro-luminescence and free radical excitation analysis.

The electrical tree in grafted polypropylene (PP) is inhibited compared with that of pure PP. To understand the free radicals that are generated during the treeing process, we study the electron paramagnetic resonance (EPR) spectra. Additionally, to provide a clearer explanation of the suppression of electrical trees, this research uses electroluminescence (EL) and excitation computation. These methods help us to observe the movement of electrons and to understand the geometric and electronic structures involved. In pure PP, the energy required to excite the electrons is approximately the same as the band gap of PP while electrons are easier to be excited in grafted PP than in pure PP, because the band gap is narrower. As a result, though the electrical tree length is shorter in PP-g-MMA, the EPR signal is more intense because of the uneven distribution of electrons.

Bio-Inspired High Sensitivity of Moisture-Mechanical GO Films with Period-Gradient Structures.

Moisture actuators can accomplish humidity-triggered energy-conversion process, through material screening and structural design. Inspired by natural caterpillars and the hydrophilic properties of graphene oxide (GO), this work proposes a geometrical design of period-gradient structures in GO films for fabricating moisture actuators. These novel period-gradient-structured GO films exhibit excellent dynamic performance that they could deform at 1000° with a small radius in several seconds at a high relative humidity (RH ≈ 80%). The properties of fast actuating speed and high response to deformation are achieved through the structural designing of the sole GO film by a one-step formation process. A mechanics-based theoretical model combined with the finite element simulation is presented to demonstrate the actuating mechanism in geometry, moisture, and mechanics, which lays the foundation for potential applications of GO films in remote control, environmental monitoring, and man-machine interactions.

Multi-functional stretchable sensors based on a 3D-rGO wrinkled microarchitecture.

The structural design of sensing active layers plays a critical role in the development of electromechanical sensors. In this study, we established an innovative concept for constructing sensors, pre-straining & laser reduction (PS&LR), based on a laser-induced wrinkle effect. This method combines and highlights the advantages of a wrinkled structure in the flexibility of sensors and the advantages of laser in the efficient reduction of GO; thus, it can efficiently introduce tunable, stretchable 3D-rGO expansion bulges in wrinkled GO films. Particularly, the sensors based on this special structure (1.5 cm × 3 cm) demonstrated a multi-functional and distinguished sensing ability in the cases of bending, stretching and touching modes. Moreover, the 3D-rGO architecture endowed the sensors with great sensitivity and design flexibility, i.e., a high sensing factor of 122, relative current value change of 60 times at the bending angle of 60°, decreased relative resistance-strain curve and diverse bending strategies for various detection purposes. Thus, the established design and preparation strategy provides large design flexibility for various promising applications.

An asymmetric graphene oxide film for developing moisture actuators.

Although Janus films of different compositions have been commonly utilized to develop moisture actuators due to the different capabilities of swelling in materials, a sole material with a distinct structural design is also able to provide moisture-actuation. In this study, we simply used graphene oxide (GO) to fabricate a sole GO film with an asymmetric structure which consisted of a wavy layer and a smooth layer. Due to the asymmetric structure and excellent hygroscopicity of the GO material, the asymmetric graphene oxide (AGO) film (2.5 × 0.5 cm2) was responsive to moisture and showed a maximum bending angle change of ≈1800° as the relative humidity (RH) changed. Compared with other reports about moisture actuators, the AGO film exhibited a superior bending capability. Furthermore, we propose a novel mechanism for moisture actuation of the AGO film based on our detailed observations, and a wavy structure has been introduced for showing great potential in bending deformation. Finally, the AGO film was used as a grabber to grab a leaf and it exhibited good capability to twine around a plastic rod. This work provides a novel pathway for the development of moisture-responsive materials for potential applications in robotics, artificial muscles and switches.