Advanced Multimaterial Electronic and Optoelectronic Fibers and Textiles

The ability to integrate complex electronic and optoelectronic functionalities within soft and thin fibers is one of today's key advanced manufacturing challenges. Multifunctional and connected fiber devices will be at the heart of the development of smart textiles and wearable devices. These devices also offer novel opportunities for surgical probes and tools, robotics and prostheses, communication systems, and portable energy harvesters. Among the various fiber-processing methods, the preform-to-fiber thermal drawing technique is a very promising process that is used to fabricate multimaterial fibers with complex architectures at micro- and nanoscale feature sizes. Recently, a series of scientific and technological breakthroughs have significantly advanced the field of multimaterial fibers, allowing a wider range of functionalities, better performance, and novel applications. Here, these breakthroughs, in the fundamental understanding of the fluid dynamics, rheology, and tailoring of materials microstructures at play in the thermal drawing process, are presented and critically discussed. The impact of these advances on the research landscape in this field and how they offer significant new opportunities for this rapidly growing scientific and technological platform are also discussed.

Microstructure examination of Fe-14Cr ODS ferritic steels produced through different processing routes

Nadine Baluc, Zbigniew Oksiuta

Various thermo-mechanical treatments were applied to refine and homogenise grain size and improve mechanical properties of hot-isostatically pressed (HIP) 14%Cr ODS ferritic steel. The grain size was reduced, improving mechanical properties, tensile strength and Charpy impact, however bimodal-like distribution was also observed. As a result, larger, frequently elongated grains with size above 1 mu m and refined, equiaxed grains with a diameter ranging from 250 to 500 nm. Neutron diffraction measurements revealed that for HIP followed by hydrostatic extrusion material the strongest fiber texture was observed oriented parallel to the extrusion direction. In comparison with hot rolling and hot pressing methods, this material exhibited promising mechanical properties: the ultimate tensile strength of 1350 MPa, yield strength of 1280 MPa, total elongation of 21.7% and Charpy impact energy of 5.8 J. Inferior Charpy impact energy of similar to 3.0J was measured for HIP and hot rolled material, emphasising that parameters of this manufacturing process still have to be optimised. As an alternative manufacturing route, due to the uniform microstructure and simplicity of the process, hot pressing might be a promising method for production of smaller parts of ODS ferritic steels. Besides, the ductile-to-brittle transition temperature of all thermo-mechanically treated materials, in comparison with as-HIPped ODS steel, was improved by more than 50%, the transition temperature ranging from 50 to 70 degrees C (323 and 343 K) remains still unsatisfactory. (C) 2014 Elsevier B.V. All rights reserved.

Elsevier Science Bv2014

Multi-material Optoelectronic Fiber Devices

Alexis Gérald Page, Yunpeng Qu, Fabien Sorin, Marco Volpi, Wei Yan

The recent ability to integrate materials with different optical and optoelectronic properties in prescribed architectures within flexible fibers is enabling novel opportunities for advanced optical probes, functional surfaces and smart textiles. In particular, the thermal drawing process has known a series of breakthroughs in recent years that have expanded the range of materials and architectures that can be engineered within uniform fibers. Of particular interest in this presentation will be optoelectronic fibers that integrate semiconductors electrically addressed by conducting materials. These long, thin and flexible fibers can intercept optical radiation, localize and inform on a beam direction, detect its wavelength and even harness its energy. They hence constitute ideal candidates for applications such as remote and distributed sensing, large-area optical-detection arrays, energy harvesting and storage, innovative health care solutions, and functional fabrics. To improve performance and device complexity, tremendous progresses have been made in terms of the integrated semiconductor architectures, evolving from large fiber solid-core, to sub-hundred nanometer thin-films, nano-filaments and even nanospheres. To bridge the gap between the optoelectronic fiber concept and practical applications however, we still need to improve device performance and integration. In this presentation we will describe the materials and processing approaches to realize optoelectronic fibers, as well as give a few examples of demonstrated systems for imaging as well as light and chemical sensing. We will then discuss paths towards practical applications focusing on two main points: fiber connectivity, and improving the semiconductor microstructure by developing scalable approaches to make fiber-integrated single-crystal nanowire based devices.

SPIE-Int Soc Optical Engineering2017

Thermal Drawing of Polymer Nano-composites: Fluid Dynamic Analysis and Application to Novel Functional Fibers

Alexis Gérald Page

The thermal drawing process is emerging as a versatile platform for the development of multimaterial fiber devices and advanced textiles for sensing, energy harvesting or medical applications, owing to the possibility to integrate insulators, conductors and various types of functional materials together in complex architectures. This field of research remains relatively recent and still has unexploited potential and unanswered questions. In particular, the lack of transparent conducting material compatible with thermal drawing has so far limited the development of optoelectronic fiber devices. It has indeed hindered the ability to fabricate the types of optoelectronic devices that require a transparent electrode, most notably photovoltaic cells. Furthermore, conductive polymer composites based on carbon black have been utilized for years as an alternative to crystalline metals that can maintain finer geometries, crystalline metals being limited by capillary instabilities due to their low viscosity in the melted state during thermal drawing. However, the observation that the conductivity of composites depends on drawing conditions has thus far not been explained through an understanding of the underlying mechanism. In this thesis, we investigate the production and thermal drawing of thermoplastic nanocomposites based on carbon black, but also on high aspect ratio conductive fillers such as silver nanowires and carbon nanotubes. The latter are indeed suitable to fabricate transparent conducting films, and we show that we can find appropriate compositions and drawing conditions to integrate them in multimaterial fibers. After looking into the thermal drawing of such composites in more details, we propose an advanced fluid dynamic analysis that accurately models the thermal drawing process, with new insights on the radial dependency of the axial velocity. We design a way to visualize the deformation in the neckdown region and show that our model compares well with the experimental observation. We use this model to further develop the theoretical approach to account for the influence of thermal drawing on the conductivity of nanocomposites. The impact of both the draw ratio and the radial position observed experimentally is explained quantitatively by the results of the model. Our approach can potentially be applied to other types of materials whose properties change under the deformation due to thermal drawing. From these findings, we demonstrate a variety of novel composite-based fiber devices. We fabricated a functional photodetecting fiber using a transparent electrode made of a carbon nanotube composite, paving the way towards the development of novel optoelectronic fiber devices that integrate transparent electrodes. Moreover, we present a new type of touch sensing fiber device that relies on a freely moving conductive domain made of a carbon black nanocomposite. Such type of electronic fiber device is capable of both detecting a pressure applied and localizing it along its entire length. We can envision applications in soft electronics or healthcare with individual fiber devices or by embedding them in smart textiles.