Mechanical Reinforcement of Electrospun Poly(Vinyl Alcohol) by a-FeOOH Nanowires

Anna Sutka, Martin Jarvekulg, Andris Sutka, Ivo Heinmaa, Uno Maeorg, Krisjanis Smits, Martin Timusk

We report the mechanical performance of α-FeOOH nanowire reinforced poly(vinyl alcohol) (PVA) composite nanofiber mat, fabricated using straightforward aqueous processing methods. Goethite (α-FeOOH) nanocrystals have a high elastic modulus and –OH rich surface, ensuring strong interactions with hydrophilic polymers and effective reinforcement. Needle-less electrospinning resulted in alignment of the nanowires along fibre axis, as confirmed by transmittance electron microscopy studies. Produced composite PVA nanofibers containing 10 wt% goethite nanoparticles exhibited an outstanding fivefold increase in Young’s modulus and 2.5-fold improvement of tensile strength compared to mats of neat PVA. The addition of α-FeOOH had a significant influence on glass transition temperature indicating formation of interphase regions around nanowire inclusions. Observed properties are explained by nanowire grafting in the precursor solution, extensive interactions between the adsorbed PVA chains and the matrix and percolation of interphase regions at 10 wt% α-FeOOH.

Published in Polymer Composites, John Wiley and Sons Ltd.

DOI: 10.1002/pc.24231

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Unexpected Epitaxial Growth of a Few WS2 Layers on 1100 Facets of ZnO Nanowires

Boris Polyakov, Alexei Kuzmin, Krisjanis Smits, Janis Zideluns, Edgars Butanovs,
Jelena Butikova, Sergei Vlassov, Sergei Piskunov, and Yuri F. Zhukovskii


Core-shell nanowires is an interesting and perspective class of radially heterostructured nanomaterials where epitaxial growth of the shell can be realized even at signi ficant core-shell lattice mismatch. In this study epitaxial hexagonally-shaped shell consisting of WS2 nanolayers was grown on f1100g facets of prismatic wurtzite-structured
[0001]-oriented ZnO nanowires for the first time. A synthesis was performed by annealing in a sulfur atmosphere of ZnO/WO3 core-shell structures, produced by reactive
DC magnetron sputtering of amorphous a-WO3 layer on top of ZnO nanowire array.
The morphology and phase composition of synthesized ZnO/WS2 core-shell nanowires were con firmed by scanning and transmission electron microscopy (SEM and TEM),micro-Raman and photoluminescence spectroscopy. Epitaxial growth of WS2(0001) layer(s) on f1100g facets of ZnO nanowire is unexpected due to incompatibility of their symmetry and structure parameters. To relax the interfacial incoherence, we propose a model of ZnO/WS2 interface containing WS2 bridging groups inside and use first-principles simulations to support its feasibility.

J. Phys. Chem. C

DOI: 10.1021/acs.jpcc.6b06139

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Complex tribomechanical characterization of ZnO nanowires: nanomanipulations supported by FEM simulations

Sergei Vlassov, Boris Polyakov, Sven Oras, Mikk Vahtrus,
Mikk Antsov, Andris Šutka Krisjanis Smits, Leonid M Dorogin and
Rünno Lõhmus

In the present work, we demonstrate a novel approach to nanotribological measurements based
on the bending manipulation of hexagonal ZnO nanowires (NWs) in an adjustable halfsuspended
configuration inside a scanning electron microscope. A pick-and-place manipulation
technique was used to control the length of the adhered part of each suspended NW. Static and
kinetic friction were found by a ‘self-sensing’ approach based on the strain profile of the
elastically bent NW during manipulation and its Young’s modulus, which was separately
measured in a three-point bending test with an atomic force microscope. The calculation of static
friction from the most bent state was completely reconsidered and a novel more realistic crackbased
model was proposed. It was demonstrated that, in contrast to assumptions made in
previously published models, interfacial stresses in statically bent NW are highly localized and
interfacial strength is comparable to the bending strength of NW measured in respective bending

Nanotechnology 27 (2016) 335701 (10pp)


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