Lasers are nowadays widely applied in additive manufacturing and several laser based techniques related to inkjet printing are emerging. In this paper, surface treatment of nanoparticle coatings using a commercial laser engraving machine are presented. Experiments were performed on (i) thin thermally cured silver nanoparticle coatings on glass and (ii) iron oxide (Fe2O3) nanoparticle dispersion coatings on glass. The laser treatment on Ag films illustrates local melting or dewetting behavior dependent on laser power and on the density of engraving patterns. For Fe2O3 coatings, direct laser writing on dried layers and laser treatment on fluid nanoparticle ink layers are investigated. We demonstrate and discuss in particular the generation of large area laser induced microstructures in vertically confined nanoparticle ink films. Controlled ink accumulation is generated by the laser pulses. Furthermore, 2D porous network structures, as well as laser induced large area filament structures are generated by heat driven capillary flow. Tailored adjustments of nanoparticle inks, film thickness and laser treatment patterns open perspectives for the generation of laser induced self-assemblies, e.g. for novel fabrication processes for 2D metamaterials, for sensor developments or advanced anti-counterfeit applications.
Conductive polymers are promising for application in the medical and sport sectors, e.g. for thin wearable health monitoring systems. While many today’s electrodes contain either carbon or metals as electrically conductive filler materials, product design manufacturing has an increasing interest in the development of metal free and carbon free, purely polymer based electrode materials. While conducting polymers have generally rather low electrical conductivities compared to metals or carbon, they offer broad options for industrial processing, as well as for dedicated adjustments of final product properties and design aspect, such as colour, water repellence, or mechanical flexibility in addition to their electrical properties. The development of electrically conducting polymer blends, based on conductive polymers is thus timely and of high importance for the design of new attractive flexible electrodes. We have developed material formulation and processing techniques for the fabrication of self-supporting thin film electrodes based on polyaniline (PANI) and polyvinylidene fluoride (PVDF) blends. Electrical four-point probing was used to evaluate the electrode conductivity for different processing and fabrication techniques. Optical microscopy and atomic force microscopy measurements corroborate the observed electrical conductivity obtained even at low PANI concentrations revealing the nanoscale material distribution within the blends. Our self-supporting thin film electrodes are flexible, smooth, and water repellent and were furthermore successfully tested under bending and upon storage over a period of several months. This opens new perspectives for the design of metal free and carbon free flexible electrodes for medical, health, and sports applications.
Flexible electrodes play an increasing role for medical applications, such as ECG (electrocardiography) or TENS (Transcutaneous electrical nerve stimulation) due to comfort in use and thus their suitability for health monitoring under movement and during sport. Polymers, such as polyvinylidene fluoride (PVDF), are promising for the development of fabrication methods and materials for such application cases, as stable flexible thin polymer membranes can be produced at large scale. We have compared different up-scalable fabrication techniques of thin electrode membranes based on PVDF as a function of silver nanowire concentration, using electrospinning, spincoating, and drop-casting techniques. The produced thin films and membranes and thin films were investigated by electrical four-point probing, optical microscopy, atomic force microscopy, as well as by stability tests under bending, and water exposure. We show, that a combination of electrospinning and spin-coating presents a reliable method for the fabrication of AgNW-PVDF based flexible nanofiber membrane electrodes (NMEs). Our nanofiber membrane electrodes (NMEs) exhibit a 10 times lower sheet resistance than AgNW-PVDF thin film electrodes (TFEs) produced for comparisons by a combination of spincoating and drop-casting using the same amounts of AgNWs. Upon immersion in water for up to 48 hours, we do not detect any nanowire release or decomposition of the fabricated electrodes, which is promising in view of application of the AgNW-PVDF composite electrodes in humid environment.
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