Markus Beckers

Spinnability and Characteristics of Polyvinylidene Fluoride (PVDF)-based Bicomponent Fibers with a Carbon Nanotube (CNT) Modified Polypropylene Core for Piezoelectric Applications

This research explains the melt spinning of bicomponent fibers, consisting of a conductive polypropylene (PP) core and a piezoelectric sheath (polyvinylidene fluoride). Previously analyzed piezoelectric capabilities of polyvinylidene fluoride (PVDF) are to be exploited in sensor filaments. The PP compound contains a 10 wt % carbon nanotubes (CNTs) and 2 wt % sodium stearate (NaSt). The sodium stearate is added to lower the viscosity of the melt. The compound constitutes the fiber core that is conductive due to a percolation CNT network. The PVDF sheath’s piezoelectric effect is based on the formation of an all-trans conformation β phase, caused by draw-winding of the fibers. The core and sheath materials, as well as the bicomponent fibers, are characterized through different analytical methods. These include wide-angle X-ray diffraction (WAXD) to analyze crucial parameters for the development of a crystalline β phase. The distribution of CNTs in the polymer matrix, which affects the conductivity of the core, was investigated by transmission electron microscopy (TEM). Thermal characterization is carried out by conventional differential scanning calorimetry (DSC). Optical microscopy is used to determine the fibers’ diameter regularity (core and sheath). The materials’ viscosity is determined by rheometry. Eventually, an LCR tester is used to determine the core’s specific resistance.

Simple and adjustable fabrication process for graded-index polymer optical fibers with tailored properties for sensing

A simple and versatile fabrication process for graded-index polymer optical fibers (GI-POF) is presented that is continuous and allows for cheap sensor fibers with adjusted properties for particular sensor applications. The fabrication process is based on conventional melt-spinning with subsequent rapid cooling of the filament in order to introduce a temperature gradient within the fiber. This will result in a density and finally in a refractive-index profile. By adjusting the temperature of the water quench for cooling the refractive-index profile can be controlled in from almost step index to graded index. By a combination of process parameters like temperature, spinning speed and elongation the scattering can be influenced in order to obtain fibers for illumination or collecting light for irradiance sensors. Since the fabrication method is adjusted from textile manufacturing it can be included into textiles for wearable sensors or flexible sensing surfaces.

Adjoint Mode Computation of Subgradients for McCormick Relaxations

In Mitsos et al. (SIAM Journal on Optimization 20(2):573–601, 2009), a method similar to Algorithmic Differentiation (AD) is presented which allows the propagation of, in general nondifferentiable, McCormick relaxations (McCormick, Mathematical Programming 10(2):147–175, 1976; Steihaug, Twelfth Euro AD Workshop, Berlin, 2011) of factorable functions and of the corresponding subgradients in tangent-linear mode. Subgradients are natural extensions of “usual” derivatives which allow the application of derivative-based methods to possibly nondifferentiable convex and concave functions. The software package libMC (Mitsos et al. SIAM Journal on Optimization 20(2):573–601, 2009) performs the automatic propagation of the relaxation and of corresponding subgradients based on the principles of tangent-linear mode AD by overloading. Similar ideas have been ported to Fortran yielding modMC as part of our ongoing collaboration with the authors of Mitsos et al. (SIAM Journal on Optimization 20(2):573–601, 2009). In this article an adjoint method for the computation of subgradients for McCormick relaxations is presented. A corresponding implementation by overloading in Fortran is provided in the form of amodMC. The calculated subgradients are used in a deterministic global optimization algorithm based on a branch-and-bound method. The superiority of adjoint over tangent-linear mode is illustrated by two examples.

Fabrication techniques for polymer optical fibres

Abstract There are a lot of different possibilities to manufacture polymer optical fibres. Regarding the final application, such as data transmission, lighting, or sensors, and the requirements concerning the polymer optical fibres, it is distinguished between step-index polymer optical fibres and graded-index polymer optical fibres. This chapter briefly summarizes the existing manufacturing techniques for step-index and graded-index polymer optical fibres and compares the advantages and the disadvantages of each process. At first the discontinuous manufacturing techniques for polymer optical fibres are discussed. These include preform production, heat drawing and batch extrusion. Finally the continuous manufacturing techniques are discussed. These include continuous extrusion, photochemical polymerization, co-extrusion, dry-spinning, melt-spinning and a modified melt-spinning process for the production of graded-index polymer optical fibres.

Dopant-free fabrication process for graded-index polymer optical fiber solely based on temperature treatment

A simple continuous fabrication process for graded-index polymer optical fibers is presented that does not rely on dopants to form the refractive-index profile. A conventional melt-spinning process is followed by rapid cooling. This will result in a density gradient and finally in a refractive-index profile.

Novel Melt-Spun Polymer-Optical Poly(methyl methacrylate) Fibers Studied by Small-Angle X-ray Scattering

The structural properties of novel melt-spun polymer optical fibers (POFs) are investigated by small-angle X-ray scattering. The amorphous PMMA POFs were subjected to a rapid cooling in a water quench right after extrusion in order to obtain a radial refractive index profile. Four fiber samples were investigated with small-angle X-ray scattering (SAXS). The resulting distance-distribution functions obtained from the respective equatorial and meridional SAXS data exhibit a real-space correlation peak indicative of periodic cross-sectional and axial variations in the scattering density contrast. Simple model calculations demonstrate how the structural information contained particularly in the equatorial distance distribution function can be interpreted. The respective results are qualitatively verified for one of the fiber samples by comparison of the model curve with the measured SAXS data. Eventually, the study confirms that the cross-sectional variation of the (scattering-) density is the main reason for the formation of radial refractive-index profiles in the POFs.

Overview of the POF market

While there are several studies about the polymer-optical fibre (POF) market as a whole including eg, connectors, cables, transceivers, light sources, optics, couplers and even installation and maintenance, there is hardly any data about the actual POF market itself. By means of expert interviews this chapter focuses on the POF market as well as its manufacturers and their products. The chapter shall provide an overview on the market and its major players, and plots market volumes and current unit prices subject to differentiating factors such as application fields, region, function and material.

Applications of polymer-optical fibres in sensor technology, lighting and further applications

Optical fibres have a broad application potential in data transmission, as sensor fibres and in lighting technology. This chapter gives an introduction of functional principles of the three mentioned fields. Besides, integration of polymer-optical fibres (POFs) in smart textiles is one of the most challenging spheres in the multidisciplinary research that incorporates the know-how in textile engineering, material science, electronics, computer science and other studies. The idea of smart textiles is to integrate an additional value into a product through increasing its functionality. POF technology remains the one to be likely addressed for the implementation of sensors and actuators. The end-use of such intelligent structures varies from civil engineering to healthcare. POFs are also the materials to be used for data transfer. Finally, optics technology is the one that arouses great interest and demand in fashion and design.

Noncircular side-emitting fibres for directed lighting

We present a novel fiber type with a trilobal, non-circular cross section. The fiber is designed for illumination purposes with a special shape in order to form a distinct asymmetrical radiation pattern, which can be used to concentrate light on particular locations in order to cure resins or polymers but can also find its applications for illumination purposes.

Introduction – why we made this book

This chapter gives an introduction to the book. Starting with a brief history of communication and optical communication in particular the background is prepared for the rapidly developing techniques in polymer-optical fibres. We conclude the chapter with a list of the chapters to come and the motivation behind each of them.