Multifunctional capability, flexible design, rugged lightweight construction and self-powered operation are desired attributes for electronics that directly interface with the human body or with advanced robotic systems. For these applications, piezoelectric materials, in forms that offer the ability to bend and stretch, are attractive for pressure/force sensors and mechanical energy harvesters. Here, we introduce a large area, flexible piezoelectric material that consists of sheets of electrospun fibres of the polymer poly(vinylidenefluoride-co-trifluoroethylene). The flow and mechanical conditions associated with the spinning process yield free-standing, three-dimensional architectures of aligned arrangements of such fibres, in which the polymer chains adopt strongly preferential orientations. The resulting material offers exceptional piezoelectric characteristics, to enable ultra-high sensitivity for measuring pressure, even at exceptionally small values (0.1 Pa). Quantitative analysis provides detailed insights into the pressure sensing mechanisms, and establishes engineering design rules. Potential applications range from self-powered micro-mechanical elements, to self-balancing robots and sensitive impact detectors.

Electrospun nanofibers are extensively studied and their potential applications are largely demonstrated. Today, electrospinning equipment and technological solutions, and electrospun materials are rapidly moving to commercialization. Dedicated companies supply laboratory and industrial‐scale components and apparatus for electrospinning, and others commercialize electrospun products. This paper focuses on relevant technological approaches developed by research, which show perspectives for scaling‐up and for fulfilling requirements of industrial production in terms of throughput, accuracy, and functionality of the realized nanofibers. A critical analysis is provided about technological weakness and strength points in combination with expected challenges from the market. magnified image

Organic materials have revolutionized optoelectronics by their processability, flexibility and low cost, with application to light-emitting devices for full-colour screens, solar cells and lasers. Some low-dimensional organic semiconductor structures exhibit properties resembling those of inorganics, such as polarized emission and enhanced electroluminescence. One-dimensional metallic, III-V and II-VI nanostructures have also been the subject of intense investigation as building blocks for nanoelectronics and photonics. Given that one-dimensional polymer nanostructures, such as polymer nanofibres, are compatible with sub-micrometre patterning capability and electromagnetic confinement within subwavelength volumes, they can offer the benefits of organic light sources to nanoscale optics. Here we report on the optical properties of fully conjugated, electrospun polymer nanofibres. We assess their waveguiding performance and emission tuneability in the whole visible range. We demonstrate the enhancement of the fibre forward emission through imprinting periodic nanostructures using room-temperature nanoimprint lithography, and investigate the angular dispersion of differently polarized emitted light.

We report on the wettability properties of silicon surfaces, simultaneously structured on the micrometre-scale and the nanometre-scale by femtosecond (fs) laser irradiation to render silicon hydrophobic. By varying the laser fluence, it was possible to control the wetting properties of a silicon surface through a systematic and reproducible variation of the surface roughness. In particular, the silicon–water contact angle could be increased from 66° to more than 130°. Such behaviour is described by incomplete liquid penetration within the silicon features, still leaving partially trapped air inside. We also show how controllable design and tailoring of the surface microstructures by wettability gradients can drive the motion of the drop’s centre of mass towards a desired direction (even upwards).

Piezoelectric polymers are promising energy materials for wearable and implantable applications for replacing bulky batteries in small and flexible electronics. Therefore, many research studies are focused on understanding the behavior of polymers at a molecular level and designing new polymer-based generators using polyvinylidene fluoride (PVDF). In this work, we investigated the influence of voltage polarity and ambient relative humidity in electrospinning of PVDF for energy-harvesting applications. A multitechnique approach combining microscopy and spectroscopy was used to study the content of the β-phase and piezoelectric properties of PVDF fibers. We shed new light on β-phase crystallization in electrospun PVDF and showed the enhanced piezoelectric response of the PVDF fiber-based generator produced with the negative voltage polarity at a relative humidity of 60%. Above all, we proved that not only crystallinity but also surface chemistry is crucial for improving piezoelectric performance in PVDF fibers. Controlling relative humidity and voltage polarity increased the d 33 piezoelectric coefficient for PVDF fibers by more than three times and allowed us to generate a power density of 0.6 μW·cm –2 from PVDF membranes. This study showed that the electrospinning technique can be used as a single-step process for obtaining a vast spectrum of PVDF fibers exhibiting different physicochemical properties with β-phase crystallinity reaching up to 74%. The humidity and voltage polarity are critical factors in respect of chemistry of the material on piezoelectricity of PVDF fibers, which establishes a novel route to engineer materials for energy-harvesting and sensing applications.

Keyword: polylactic acid, electrospinning method, thermal stimulated current, piezoelectric-like effect 1. Introduction Polylactic acid (PLA) is a biodegradable thermoplastic polyester that may be derived from renewable resources. In our previous study, PLA fiber was used in order to fabricate a film actuator. A notable feature of PLA is its biodegradability [1] , although it is also well known that PLA exhibits piezo-electric-like properties. Because of the fact that a lactide monomer exhibits chirality, two types of optical isomer exist, L-lactide and D-lactide. PLAs that polymerize to form either poly-L-lactide (PLLA) or poly-D-lactide (PDLA) also exhibit chirality. It is commonly known that using stretching to orient PLLA and PDLA films results in a shear piezoelectric effect [2-6]. On the other hand, PLA containing D-and L-lactide, i.e., poly(DL-lactic acid) (PDLLA) as racemic mixture, does not exhibit piezoelectricity. We previously reported on the actuation behavior of a randomly oriented electrospun fibrous PDLLA film [7]. This film exhibited an inverse piezoelectric-like behavior, despite its non-piezoelectric, racemic PDLLA content. Fibrous PDLLA films were prepared using the electrospinning method [8,9] , which is a simple method for preparing polymer nanofibers. The fibers that are ejected from a

The processing, properties, and applications of electrospun light‐emitting nanofibers are reviewed. The different experimental approaches for electrospinning conjugated polymers and light‐emitting compounds are presented. The characterization of the optoelectronic properties of electrospun conjugated polymer nanofibers evidences intriguing features, such as polarized emission, self‐waveguiding, enhanced energy transfer, and charge transport. The applications of such nanostructured materials include polarized light sources for lab‐on‐chip devices, nanoscale organic light‐emitting diodes and optically pumped lasers, field‐effect transistors, and high‐performance optical sensors. Future challenges and perspectives of electrospun light‐emitting nanofibers are also discussed.

The combination of materials with targeted optical properties and of complex, 3D architectures, which can be nowadays obtained by additive manufacturing, opens unprecedented opportunities for developing new integrated systems in photonics and optoelectronics. The recent progress in additive technologies for processing optical materials is here presented, with emphasis on accessible geometries, achievable spatial resolution, and requirements for printable optical materials. Relevant examples of photonic and optoelectronic devices fabricated by 3D printing are shown, which include light‐emitting diodes, lasers, waveguides, optical sensors, photonic crystals and metamaterials, and micro‐optical components. The potential of additive manufacturing applied to photonics and optoelectronics is enormous, and the field is still in its infancy. Future directions for research include the development of fully printable optical and architected materials, of effective and versatile platforms for multimaterial processing, and of high‐throughput 3D printing technologies that can concomitantly reach high resolution and large working volumes.