The electroactive β-phase in Poly (vinylidene fluoride, PVDF) is the most desirable conformation due to its highest pyro- and piezoelectric properties, which make it feasible to be used as flexible sensors, wearable electronics, and energy harvesters etc. In this study, we successfully developed a method to obtain high-content β-phase PVDF films and nanofiber meshes by mechanical stretching and electric spinning. The phase transition process and pyro- and piezoelectric effects of stretched films and nanofiber meshes were characterized by monitoring the polarized light microscopy (PLM) images, outputting currents and open-circuit voltages respectively, which were proved to be closely related to stretching ratio (λ) and concentrations. This study could expand a new route for the easy fabrication and wide application of PVDF films or fibers in wearable electronics, sensors, and energy harvesting devices.

The relaxation behaviors of thin polymer films show a strong dependence on temperature and film thickness. Direct quantitative detection of the relaxation behaviors of thin polymer films at nanometer scale by traditional instruments is however challenging. In this study, we employed atomic force microscopy (AFM)-based force-distance curve to study the relaxation dynamics and the film thickness dependence of glass transition temperature (T g ) for normal thin polystyrene (PS) films supported on silicon substrate. The adhesion force (Fad) between AFM tip and normal thin PS film surfaces was quantitatively detected in situ under the variation of temperature and film thickness. The T g of normal thin PS film was successfully obtained by the abrupt variation of Fad under temperature stimulation. Our result showed that the T g of normal thin PS films decreased with the decreasing film thickness. The study here could be beneficial for understanding the relaxation dynamics of normal thin polymer films.

LiNbO₃ (LN) crystal has been widely used as a pyroelectric material due to its spontaneous electric polarization, which could be recharged easily and can directly convert heat energy into electricity. LN crystal’s heat-resistant, low-cost, and low dielectric loss properties make it possible for its applications in room-temperature pyroelectric devices and thermal sensors. However, LN crystal suffers from fragility, inflexibility, and other mechanical properties, which limit its suitability for many applications in various fields. In this study, the LN modified flexible pyroelectric films, composed of LN micro-particles, polypropylene (PP) matrix, and multiwalled carbon nanotubes (MWCNTs), are successfully fabricated. The pyroelectric effects of LN crystal and LN/PP/MWCNT composite films are characterized by monitoring the patterned self-assembly of nanoparticles and the output pyroelectric currents. The excellent pyroelectric properties of the composites have potential applications in energy harvesters or sensors.

The stir-frying process in Chinese cooking has produced serious emissions of oily particles, which are an important source of urban air pollution. In particular, the complex composition of fine particulate may pose a threat to human respiratory and immune systems. However, current filtration methods for oily particulate fumes have low filtration efficiency, high resistance, and high equipment costs. In polypropylene (PP) electret filters, efficiency rapidly decreases and pressure drop (wind resistance) sharply increases after the adsorption of oily particles, due to the oleophilic properties of the PP fibre. We addressed this issue of filter performance degradation by fabricating a sodium perfluorooctanoate (SPFO) oleophobic coating on polyvinylidene fluoride (PVDF) fibre membranes for oily particle filtration. The SPFO coating showed a promising oleophobic effect even at low concentrations, which suggests it has oleophobic properties for different oil types and can be modified for different substrates. This fabricated oleophobic coating is thermostable and the oleophobic effect is unaffected by temperatures from 0 to 100 °C. By modifying the SPFO coating on the PVDF membrane, a high filtration efficiency (89.43%) and low wind resistance (69 Pa) was achieved without oil adhesion, so the proposed coating can be applied in the filtration and purification of oily fine particles and offers a potential strategy for preventing atmospheric oil pollution.

The rapid development of nanoscience and nanotechnology involves polymer films with thickness down to nanometer scale. However, the properties of ultrathin polymer films are extremely different from that of bulk matrix or thin films. It is challenging to distinguish the changes of physical properties in ultrathin films using conventional techniques especially when it locates near the glass transition temperature (T g). In this work, we successfully evaluated a series of physical properties of ultrathin polystyrene (PS) films by in situ characterizing the discharging behavior of the patterned charges using electric force microscopy. By monitoring the surface potential in real time, we found that the T g of ultrathin PS films is clearly independent of film thickness, which are greatly different from that of thin PS films (film thickness larger than 10 nm).