TY - JOUR AB - Nanofiber mats can be electrospun by different techniques, usually subdivided into needle-based and needleless. The latter allow for producing large-area nanofiber mats, e.g., with a width of 50 cm and lengths of several meters, if electrospinning proceeds for several hours, depending on the required thickness. Even spinning smaller samples, however, raises the question of homogeneity, especially if defined mechanical properties or a defined thickness is required, e.g., for filtration purposes. Very often, only the inner parts of such electrospun nanofiber mats are used to avoid too high variation of the nanofiber mat thickness. For this study, we used wire-based electrospinning to prepare nanofiber mats with slightly varying spinning parameters. We report investigations of the thickness and mass per unit area, measured on different positions of needleless electrospun nanofiber mats. Martindale abrasion tests on different positions are added as a measure of the mechanical properties. All nanofiber mats show unexpectedly strong variations of thickness, mass per unit area, and porosity, as calculated from the apparent density of the membranes. The thickness especially varied by nearly one order of magnitude within one sample, while the apparent density, as the most uniform parameter, still showed variations by more than a factor of two within one sample. This shows that even for apparently highly homogeneous areas of such nanofiber mats, variations cannot be neglected for all potential applications. AU - Morina, Edona AU - Dotter, Marius AU - Döpke, Christoph AU - Kola, Ilda AU - Spahiu, Tatjana AU - Ehrmann, Andrea ID - 3595 IS - 18 JF - Nanomaterials TI - Homogeneity of Needleless Electrospun Nanofiber Mats VL - 13 ER - TY - JOUR AB - Exchange bias (EB) is a unidirectional anisotropy occurring in exchange-coupled ferromagnetic/antiferromagnetic systems, such as thin films, core–shell particles, or nanostructures. In addition to a horizontal shift of the hysteresis loop, defining the exchange bias, asymmetric loops and even vertical shifts can often be found. While the effect is used in hard disk read heads and several spintronics applications, its origin is still not fully understood. Especially in nanostructures with their additional shape anisotropies, interesting and often unexpected effects can occur. Here, we provide an overview of the most recent experimental findings and theoretical models of exchange bias in nanostructures from different materials. AU - Blachowicz, Tomasz AU - Ehrmann, Andrea AU - Wortmann, Martin ID - 3488 IS - 17 JF - Nanomaterials KW - exchange bias (EB) KW - hysteresis loop shift KW - coercivity KW - ferromagnet KW - antiferromagnet KW - coercive field KW - asymmetric hysteresis loop TI - Exchange Bias in Nanostructures: An Update VL - 13 ER - TY - JOUR AB - Horizontally shifted and asymmetric hysteresis loops are often associated with exchange-biased samples, consisting of a ferromagnet exchange coupled with an antiferromagnet. In purely ferromagnetic samples, such effects can occur due to undetected minor loops or thermal effects. Simulations of ferromagnetic nanostructures at zero temperature with sufficiently large saturation fields should not lead to such asymmetries. Here we report on micromagnetic simulations at zero temperature, performed on sputtered nanoparticles with different structures. The small deviations of the systems due to random anisotropy orientations in the different grains can not only result in strong deviations of magnetization reversal processes and hysteresis loops, but also lead to distinctly asymmetric, horizontally shifted hysteresis loops in purely ferromagnetic nanoparticles. AU - Detzmeier, Joscha AU - Königer, Kevin AU - Blachowicz, Tomasz AU - Ehrmann, Andrea ID - 1614 IS - 3 JF - Nanomaterials KW - pseudo-exchange bias KW - minor loop KW - micromagnetic simulation KW - OOMMF KW - spintronics TI - Asymmetric Hysteresis Loops in Structured Ferromagnetic Nanoparticles with Hard/Soft Areas VL - 11 ER - TY - JOUR AB - Combining clusters of magnetic materials with a matrix of other magnetic materials is very interesting for basic research because new, possibly technologically applicable magnetic properties or magnetization reversal processes may be found. Here we report on different arrays combining iron and nickel, for example, by surrounding circular nanodots of one material with a matrix of the other or by combining iron and nickel nanodots in air. Micromagnetic simulations were performed using the OOMMF (Object Oriented MicroMagnetic Framework). Our results show that magnetization reversal processes are strongly influenced by neighboring nanodots and the magnetic matrix by which the nanodots are surrounded, respectively, which becomes macroscopically visible by several steps along the slopes of the hysteresis loops. Such material combinations allow for preparing quaternary memory systems, and are thus highly relevant for applications in data storage and processing. AU - Sudsom, Devika AU - Ehrmann, Andrea ID - 1624 IS - 2 JF - Nanomaterials KW - micromagnetic simulation KW - OOMMF KW - nanodots KW - antidots KW - array KW - spintronics TI - Micromagnetic Simulations of Fe and Ni Nanodot Arrays Surrounded by Magnetic or Non-Magnetic Matrices VL - 11 ER - TY - JOUR AB - Electrospun nanofiber mats may serve as new hardware for neuromorphic computing. To enable data storage and transfer in them, they should be magnetic, possibly electrically conductive and able to respond to further external impulses. Here we report on creating magnetic nanofiber mats, consisting of magnetically doped polymer nanofibers for data transfer and polymer beads containing larger amounts of magnetic nanoparticles for storage purposes. Using magnetite and iron nickel oxide nanoparticles, a broad range of doping ratios could be electrospun with a needleless technique, resulting in magnetic nanofiber mats with varying morphologies and different amounts of magnetically doped beads. AU - Döpke, Christoph AU - Grothe, Timo AU - Steblinski, Pawel AU - Klöcker, Michaela AU - Sabantina, Lilia AU - Kosmalska, Dorota AU - Blachowicz, Tomasz AU - Ehrmann, Andrea ID - 1065 IS - 1 JF - Nanomaterials TI - Magnetic Nanofiber Mats for Data Storage and Transfer VL - 9 ER - TY - JOUR AB - Pleurotus ostreatus is a well-known edible mushroom species which shows fast growth. The fungus can be used for medical, nutritional, filter, or packaging purposes. In this study, cultivation experiments were carried out with Pleurotus ostreatus growing on polyacrylonitrile (PAN) nanofiber mats in the presence of saccharose and Lutrol F68. The aim of this study was to find out whether modified PAN nanofiber mats are well suited for the growth of fungal mycelium, to increase growth rates and to affect mycelium fiber morphologies. Our results show that Pleurotus ostreatus mycelium grows on nanofiber mats in different morphologies, depending on the specific substrate, and can be used to produce a composite from fungal mycelium and nanofiber mats for biomedical and biotechnological applications. AU - Sabantina, Lilia AU - Kinzel, Franziska AU - Hauser, Thomas AU - Többer, Astrid AU - Klöcker, Michaela AU - Döpke, Christoph AU - Böttjer, Robin AU - Wehlage, Daria AU - Rattenholl, Anke AU - Ehrmann, Andrea ID - 1061 IS - 3 JF - Nanomaterials TI - Comparative Study of Pleurotus ostreatus Mushroom Grown on Modified PAN Nanofiber Mats VL - 9 ER - TY - JOUR AB - Electrospinning is a new technology whose scope is gradually being developed. For this reason, the number of known polymer–solvent combinations for electrospinning is still very low despite the enormous variety of substances that are potentially available. In particular, electrospinning from low-toxic solvents, such as the use of dimethyl sulfoxide (DMSO) in medical technology, is rare in the relevant scientific literature. Therefore, we present in this work a series of new polymers that are applicable for electrospinning from DMSO. From a wide range of synthetic polymers tested, poly(vinyl alcohol) (PVOH), poly(2ethyl2oxazolene) (PEOZ), and poly(vinylpyrrolidone) (PVP) as water-soluble polymers and poly(styrene-co-acrylonitrile) (SAN), poly(vinyl alcohol-co-ethylene) (EVOH), and acrylonitrile butadiene styrene (ABS) as water-insoluble polymers were found to be suitable for the production of nanofibers. Furthermore, the influence of acetone as a volatile solvent additive in DMSO on the fiber morphology of these polymers was investigated. Analyses of the fiber morphology by helium ion microscopy (HIM) showed significantly different fiber diameters for different polymers and a reduction in beads and branches with increasing acetone content. AU - Wortmann, Martin AU - Frese, Natalie AU - Sabantina, Lilia AU - Petkau, Richard AU - Kinzel, Franziska AU - Gölzhäuser, Armin AU - Moritzer, Elmar AU - Hüsgen, Bruno AU - Ehrmann, Andrea ID - 1066 IS - 1 JF - Nanomaterials TI - New Polymers for Needleless Electrospinning from Low-Toxic Solvents VL - 9 ER - TY - JOUR AB - Electrospinning can be used to create nanofiber mats for diverse applications, from wound dressings and tissue engineering to filters for medical and biotechnological applications. In most of these applications, it is necessary to fix the nanofiber mat on a macroscopic textile fabric, on another nanofiber mat or within a frame to keep it at the desired position. Due to their extremely low thickness and areal mass, however, nanofiber mats are easily destroyed by sewing, and in several situations glued bonds are too thick and not flexible enough. Here we report on ultrasonic welding of polyacrylonitrile nanofiber mats, suggesting this method as a joining process without destruction of the mat morphology for thermoplastic nanofiber mats. A variety of welding patterns results in different adhesion forces between both joined nanofiber mats and different failure mechanisms, with some welding patterns enabling bonding stronger than the mats themselves. Our findings show that ultrasonic welding is a possible joining method for polyacrylonitrile nanofiber mats. AU - Wirth, Emilia AU - Sabantina, Lilia AU - Weber, Marcus AU - Finsterbusch, Karin AU - Ehrmann, Andrea ID - 1073 IS - 10 JF - Nanomaterials TI - Preliminary Study of Ultrasonic Welding as a Joining Process for Electrospun Nanofiber Mats VL - 8 ER -