Aerosol Jet Printing (AJP) is an emerging contactless direct write approach aimed at the production of fine features on a wide range of substrates. Originally developed for the manufacture of electronic circuitry, the technology has been explored for a range of applications, including, active and passive electronic components, actuators, sensors, as well as a variety of selective chemical and biological responses. Freeform deposition, coupled with a relatively large stand-off distance, is enabling researchers to produce devices with increased geometric complexity compared to conventional manufacturing or more commonly used direct write approaches. Wide material compatibility, high resolution and independence of orientation have provided novelty in a number of applications when AJP is conducted as a digitally driven approach for integrated manufacture. This overview of the technology will summarise the underlying principles of AJP, review applications of the technology and discuss the hurdles to more widespread industry adoption. Finally, this paper will hypothesise where gains may be realised through this assistive manufacturing process.
Aerosol jet printing (AJP) is a versatile technique suitable for large-area, fine-feature patterning of both rigid and flexible substrates with a variety of functional inks. In particular, AJP can tolerate ink viscosities between 1 and 1000 cP, with printing resolution of the order of 10 μm, thus making it attractive for flexible and printed electronics. This work investigates in detail significant aspects of inksubstrate combination and substrate temperature that are highly relevant to AJP. In order to do this, thin conducting silver lines are printed using AJP on both rigid (glass and silicon) as well as flexible (polyimide) substrates. The correlation between the various deposition parameters and the 'quality' of the printed lines are evaluated, through measurements of electrical conductivity under different experimental conditions. Based on our findings, a framework is proposed through which the morphology of AJP lines can be controlled and assessed for applications in large area and flexible electronic devices.
Piezoelectric materials can directly transduce electrical and mechanical energy, making them attractive for applications such as sensors, actuators and energy harvesting devices. While often associated with ceramic materials, piezoelectric behaviour is also observed in many polymers. The flexibility, ease of processing and biocompatibility of piezoelectric polymers mean that they are often preferable for certain applications, despite their lower piezoelectric coefficients. This review will cover some theoretical and practical concepts of piezoelectricity in polymers, such as the symmetry requirements, the underlying mechanism and the necessary materials processing. A brief review of the applications of piezoelectric polymers is also presented. One of the main motivations of this review is to discuss the challenges and open questions in the field in an effort to highlight potential future research directions.
Piezoelectric polymers are capable of interconverting mechanical and electrical energy, and are therefore candidate materials for biomedical applications such as sensors, actuators, and energy harvesters. In particular, nanowires of these materials are attractive as they can be unclamped, flexible and sensitive to small vibrations. Poly-l-lactic acid (PLLA) nanowires have been investigated for their use in biological applications, but their piezoelectric properties have never been fully characterised, even though macroscopic films and fibres have been shown to exhibit shear piezoelectricity. This piezoelectric mode is particularly interesting for in vivo applications where shear forces are especially relevant, and is similar to what has been observed in natural materials such as bone and DNA. Here, using piezo-response force microscopy (PFM), we report the first direct observation of shear piezoelectricity in highly crystalline and oriented PLLA nanowires grown by a novel template-wetting method. Our results are validated using finite-element simulations and numerical analysis, which importantly and more generally allow for accurate interpretation of PFM signals in soft nanostructured materials. Our work opens up the possibility for the development of biocompatible and sustainable piezoelectric nanogenerators and sensors based on polymer nanowires.
Dipole alignment in ferroelectric polymers is routinely exploited for applications in charge-based applications. Here, we present the first experimental realization of ideally ordered dipole alignment in α-phase nylon-11 nanowires. This is an unprecedented discovery as dipole alignment is typically only ever achieved in ferroelectric polymers using an applied electric field, whereas here, we achieve dipole alignment in as-fabricated nanowires of ‘non-ferroelectric’ α-phase nylon-11, an overlooked polymorph of nylon proposed 30 years ago but never practically realized. We show that the strong hydrogen bonding in α-phase nylon-11 serves to enhance the molecular ordering, resulting in exceptional intensity and thermal stability of surface potential. This discovery has profound implications for the field of triboelectric energy harvesting, as the presence of an enhanced surface potential leads to higher mechanical energy harvesting performance. Our approach therefore paves the way towards achieving robust, high-performance mechanical energy harvesters based on this unusual ordered phase of nylon-11.
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