This article describes the preparation of hierarchically structured microsieves via a suitable combination of float-casting and inkjet-printing: A mixture of hydrophobized silica particles of 600 nm ± 20 nm diameter, a suitable non-water-soluble nonvolatile acrylic monomer, a nonvolatile photoinitiator, and volatile organic solvents is applied to a water surface. This mixture spontaneously spreads on the water surface; the volatile solvents evaporate and leave behind a layer of the monomer/initiator mixture comprising a monolayer of particles, each particle protruding out of the monomer layer at the top and bottom surface. Photopolymerization of the monomer converts this mixed layer into a solid composite membrane floating on the water surface. Onto this membrane, while still floating on the water surface, a hierarchical reinforcing structure based on a photocurable ink is inkjet-printed and solidified. In contrast to the nonreinforced membrane, the reinforced membrane can easily be lifted off the water surface without suffering damage. Subsequently, the silica particles are removed, and thus, the reinforced composite membrane is converted into a reinforced microsieve of 350 nm ± 50 nm thickness bearing uniform through pores of 465 nm ± 50 nm diameter. This reinforced microsieve is mounted into a filtration unit and used to filter model dispersions: its permeance for water at low Reynolds numbers is in accordance with established theories on the permeance of microsieves and significantly above the permeance of conventional filtration media; it retains particles exceeding the pore size, while letting particles smaller than the pore size pass.
This article reports on developments in the manufacturing of heating elements by means of digital inkjet printing technology. The area coverage of the meander lines ranges from 34 lpi (lines per inch) to 51 and 102 lpi, which mainly influences the temperature distribution and homogeneity. Furthermore, the line width of the meander lines is varied between 250, 500, and 1000 μm. All heating elements are deposited by single‐pass printing of a nanoparticle silver ink with subsequent thermal sintering on a standard flexible polymer film, to demonstrate that inkjet printing allows the manufacturing of printed thin devices also on low‐cost material. The implementation of various designs allows the control of the temperature distribution and heat development. The printed structures are evaluated regarding their optical and electrical characteristics and their thermal performance is assessed using an infrared camera. This research has succeeded in developing bendable printed heaters, which reach homogeneous average temperature of 100 °C over an area of approximately 15 cm2 at a power supply of 12 V. The feasibility of the inkjet printed heaters is demonstrated by a long‐term test over several days with negligible fluctuations in the area temperature and highest stability in the resistance.
In the field of printed flexible heating elements, [1,2] there has been an increase in number of research, for example, in the area of screen-printed heating elements based on silver [3][4][5] or material composites. [6,7] Other methods are spray coating of silver-carbon composites [8] or patterned casting of silver onto flexible polymer film. [9] Only a few publications can be found in the field of inkjet-printed heaters, such as Byers et al. with silver microheaters, [10] Wang et al. with flexible transparent silver nanowire-based heating elements, [11] Huang et al. with silver nanowires for stretchable heating elements, [12] or Mitra et al. with. [13] Furthermore, the manufacturing of heating conductors on textile substrates using printing processes is a constant research subject, with the use of silver-based systems being the focus in the past. Selected examples are the application of various silver pastes to fabrics made of cotton, polyester, polyamide, viscose, and subsequent investigations with the focus on washability and abrasion, [14] screen-printed multilayer silver structures on textiles [15] or conductive pastes for portable textile heaters applied directly to the fiber by means of printing, [16] screen-printed, low-cost and patterned flexible heating element based on Ag fractal dendrites for human-wearable application, [17] and inkjet-printed heating conductors on nonwoven fabric. [18] Printed flexible heaters show high potential in many application scenarios, such as thermal management, [19,20] artificial intelligence, [21] thermochromic displays, [22] wearable thermotherapy, [23,24] and defogging or deicing of windows. [25,26] Essential for all these applications is a rapid thermal response for heating and cooling down, a definite temperature distribution and control, a high thermal stability over long time, and a working range across a wide temperature field. Hence, our goal is to focus on the reliability and stability of inkjet-printed heating elements on temperature-stable polyethylene naphthalene (PEN) or polyimide (PI) films and demonstrate their potential for high-temperature (up to 400 °C), long-lasting, accurate repetition rate, and bending stability in various resilience tests. Additionally, the adaptability and regulation of the heat development and the clear division into thermal zones by the use of design rules are illustrated.With their proven high reliability and repeatability, the inkjet-printed heaters exhibit a great potential in a multiplicity of applications with adaptable temperature ranges up to 400 °C on appropriate base substrates.
Herein, it is intended to show the effect of embedding an inkjet printed poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) track in an insulator polymer, impacting its electronic transition behavior, as a consequence of temperature variation. A transition from semiconductor‐to‐metal‐like behavior is observed, when the temperature is seen to exceed a certain value, which is of a nonchemical origin. Both the presented experimental and simulation results show how this transition really occurs. The proposed physical mechanism for explaining such a behavior is verified with good repeatability. The main conclusion indicates consideration of special precautions, while enclosing inkjet‐printed PEDOT:PSS‐based tracks or sensors operating under ambient conditions, along with fluctuations. This conclusion can potentially be applied to any other inkjet printed conductive organic polymer film embedded in an insulator that fulfills the conditions encountered in the experiments. The impact of this effect may be reduced and mitigated by using inkjet printing, in combination with other additive manufacturing technique. The results presented here are considered very important, as they lay the foundation for the correct compensation of the thermal drift of organic electronics‐based circuits.
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