#polyimides

AI accelerates development of advanced heat-dissipating polymers

A machine learning method developed by researchers from the Institute of Science Tokyo, the Institute of Statistical Mathematics, and other institutions accurately predicts liquid crystallinity of polymers with 96% accuracy. They screened over 115,000 polyimides and selected six candidates with a high probability of exhibiting liquid crystallinity. Upon successful synthesis and experimental analyses, these liquid crystalline polyimides demonstrated thermal conductivities up to 1.26 W m⁻¹ K⁻¹, accelerating the discovery of efficient thermal materials for next-generation electronics. Finding new polymer materials that can efficiently dissipate heat while maintaining high reliability is one of the biggest challenges in modern electronics. One promising solution is liquid crystalline polyimides, a special class of polymers whose molecules naturally align into highly ordered structures.

Novel thin and flexible sensor characterizes high-speed airflows on curved surfaces

The energy and transportation sector often make use of different kinds of fluid machinery, including pumps, turbines, and aircraft engines, all of which entail a high carbon footprint. This results mainly from inefficiencies in the fluid machinery caused by flow separation around curved surfaces, which are typically quite complex in nature.

To improve the efficiency of fluid machinery, one, therefore, needs to characterize near-wall flow on the curved surface to suppress this flow separation. The challenge in accomplishing this is multifold. First, conventional flow sensors are not flexible enough to fit into the curved walls of fluid machinery. Second, existing flexible sensors suitable for curved surfaces cannot detect the fluid angle (direction of flow). Moreover, these sensors are limited to only detecting flow separation at speeds less than 30 m/s.  

In a new study, Prof. Masahiro Motosuke from the Tokyo University of Science (TUS) in Japan and his colleagues, Mr. Koichi Murakami, Mr. Daiki Shiraishi and Dr. Yoshiyasu Ichikawa from TUS, in collaboration with Mitsubishi Heavy Industries, Japan, and Iwate University, Japan, took on this challenge. As Prof. Motosuke states, "Sensing the shear stress and its direction on curved surfaces, where flow separation easily occurs, has been difficult to achieve in particular without using a novel technique."

Using micro-sized cut metal wires, team forges path to new uses for terahertz waves

Japanese researchers successfully tested reflectionless, highly refractive index metasurface that may eventually be used in practical applications to send, receive, and manipulate light and radio waves in the terahertz waveband (THz). THz is measured in millionths of a meter, known as micrometers. The metasurface, an artificial two-dimensional flat material, was made of micro-sized cut metal wires of silver paste ink placed on both the front and back of a polyimide film. The team, led by Takehito Suzuki, Associate Professor at the Tokyo University of Agriculture and Technology (TUAT) Institute of Engineering, published their findings on April 29, 2021 in Optics Express.

Such flat metasurfaces represent a leap forward in the study of THz optics, because they may be flexible, adaptable to a much wider array of potential uses, and far smaller than the present generation of THz optics which rely upon naturally occurring materials that have fixed indices of refraction in the THz waveband, such as cyclo-olefin polymer, magnesium oxide, and silicon. An index of refraction of a material shows that how slow electromagnetic waves travel in the material compared to a vacuum.

Thermally conductive polyimide film: A better way to dissipate heat in electronic devices

Recently, a research team led by Prof. Tian Xingyou and Zhang Xian from the Institute of Solid State Physics, Hefei Institutes of Physical Science developed highly thermally conductive polyimide film with superior flexibility and electrical insulation.

Efficient heat management is essential to dissipate excessive heat in improving the efficiency and reliability of electronic devices. And in recent years, polymer materials have been widely used as substrate of microelectronics due to low cost, light weight and easy processing, with polyimide (PI) film being considered as a desired material for OLED flexible substrate.

However, limited by its low thermal conductivity (0.18 Wm-1K-1), PI usually needs to combine with highly thermally conductive fillers to strengthen its thermal conductivity.

In this work, the researchers used facile imidization-induced orientation method to fabricate layered PI/carbon nitride nanosheets (PI/CNNS) flexible nanocomposite films.

High-thermoresistant biopolyimides become water-soluble like starch

This is the first ever report on the syntheses of water-soluble polyimides which are derived from bio-based resources, showing high transparency, tunable mechanical strength and the highest thermoresistance in water-soluble polymers.

Water-soluble polymers are of great interest in many areas of soft materials. These soft materials have been widely used in applications related to aqueous solutions, such as dispersants, aggregation agents, thickeners, moisturizers, binders, and hydrogels. With the increase in global awareness about environmental concerns, the importance of water-soluble materials has been highlighted and thereby researchers have expanded their application windows to electronics, functional coatings, advanced adhesives and biomedical materials. Most natural polymers such as polysaccharides, polypeptides, or their derivatives are water-soluble while synthetic water-soluble polymers are also available such as poly(ethylene oxide), poly(vinyl alcohol), polyacrylates, polyacrylamide, and their derivatives. However, conventional water-soluble polymers have limited applications due to their low thermal distortion temperatures (ca. 200 °C).

Tale of the tape: Sticky bits make better batteries

Where things get sticky happens to be where interesting science happens in a Rice University lab working to improve battery technology.

Using techniques similar to those they employed to develop laser-induced graphene, Rice chemist James Tour and his colleagues turned adhesive tape into a silicon oxide film that replaces troublesome anodes in lithium metal batteries.

For the Advanced Materials study, the researchers used an infrared laser cutter to convert the silicone-based adhesive of commercial tape into the porous silicon oxide coating, mixed with a small amount of laser-induced graphene from the tape's polyimide backing. The protective silicon oxide layer forms directly on the current collector of the battery.

The idea of using tape came from previous attempts to produce free-standing films of laser-induced graphene, Tour said. Unlike pure polyimide films, the tape produced not only laser-induced graphene from the polyimide backing but also a translucent film where the adhesive had been. That caught the curiosity of the researchers and led to further experimentation.

Enhancing the performance of solar cells with 'graphene armor'

A team of researchers, affiliated with UNIST has come up with a novel electrode that could greatly improve the stability of perovskite solar cells (PSCs), the most promising candidate for the next generation solar cells due to their low cost and high power conversion efficiency. This is because inserting a protection layer between the metal-based electrode and the perovskite film can prevent metal-induced degradation and that graphene, as such a layer, can effectively suppress the diffusion of metals and halide ions.

This breakthrough was led by Professor Hyesung Park and his research team in the School of Energy and Chemical Engineering at UNIST. In their work, the research team developed a flexible metal grid-based hybrid electrode platform by using a Cu grid-embedded polyimide (CEP) film with a graphene sheet as the protection layer (GCEP), which exhibited high electrical conductivity, excellent chemical stability and mechanical durability. The development demonstrates the critical role of graphene as a protection layer to prevent metal-induced degradation and halide diffusion between the electrode and perovskite layer.

Metal oxide-based electrodes (ITOs) have been used as conventional transparent conducting electrodes, but their inflexibility causes them to be easily broken or fractured, hence making them unsuitable to wearable device applications. In particular, the major obstacle to the metal-based transparent conductive electrodes (TCE) application in PSCs is the degradation induced by the interdiffusion of metals and halide ions between the metal electrode and the perovskite layer.

Piezoelectrics stretch their potential with a method for flexible sticking

Piezoelectric materials are used for applications ranging from the spark igniter in barbeque grills to the transducers needed by medical ultrasound imaging. Thin-film piezoelectrics, with dimensions on the scale of micrometers or smaller, offer potential for new applications where smaller dimensions or a lower voltage operation are required.

Researchers at Pennsylvania State University have demonstrated a new technique for making piezoelectric microelectromechanical systems (MEMS) by connecting a sample of lead zirconate titanate (PZT) piezoelectric thin films to flexible polymer substrates. Doctoral candidate Tianning Liu and her co-authors report their results this week in the Journal of Applied Physics.

"There's a rich history of work on piezoelectric thin films, but films on rigid substrates have limitations that come from the substrate," said Thomas N. Jackson, a professor at Penn State and one of the paper's authors. "This work opens up new areas for thin-film piezoelectrics that reduce the dependence on the substrate."

The researchers grew polycrystalline PZT thin films on a silicon substrate with a zinc oxide release layer, to which they added a thin layer of polyimide. They then used acetic acid to etch away the zinc oxide, releasing the 1-micrometer thick PZT film with the polyimide layer from the silicon substrate. The PZT film on polyimide is flexible while possessing enhanced material properties compared to the films grown on rigid substrates.