Field-assisted 3D printing of multi-functional materials

The emergence of flexible, robust additive manufacturing platforms has created potentially transformative opportunities to integrate multiple functionalities: in particular, mechanical efficiency with mass transport, thermal management and conductivity. Field-assisted assembly of multi-phase materials holds promise for numerous applications, including flexible composites, patterning of cells in extracellular matrix in synthetic tissue, controlling ion transport in batteries, etc. Experiments involving acoustic field-assisted assembly of microscale particles will be used to elucidate the role of acoustic fields on structure formation, and the resulting opportunities to tailor macroscopic conductivity in novel ways. Figure 1 below illustrates results for conductive carbon fibers an elastomer matrix, with patterned lines created via acoustic focusing. A key advantage of the approach is the ability to create strong connected networks of second phase particles at volume fractions that are well-below that associated with the percolation threshold, which greatly facilitates the development of printable functional inks. In-situ and ex-situ observations of direct write printing will then be used to identify regimes that enable ‘on-the-fly’ control of microstructure during macroscopic patterning. Figure 1: (a) Acoustically patterned composites of Ag-coated glass fiber 2.6v% in 1:1 M:CH-A polymer matrix, which undergo small, recoverable changes in conductivity when deformed. (b) Unpatterned, dispersed-fiber composites made of the same components, but higher filler particle loading in order approach the conductivity of the patterned composites. The higher loading required compromises their flexibility, so that large, unpredictable, and irreversible losses in conductivity occur at relatively low strains (a 90 degree twist and normal handling resulted in failure by fracture). In flexible conductive materials there is a well-documented trade-off between conductivity and flexibility as the conductive filler loading increases which currently limits the viability of printable flexible conductors [Sekitani 2010 3.1.2, Rodgers 2010, Ray 2019]. Here we present a method for subverting this trade-off by using acoustophoresis to assemble filler particles into highly efficient percolated networks within the composites, forming conductive networks at low particle loading which have high tolerance for strain and little change in conductivity. We demonstrate that the acoustic patterning process simultaneously decreases the fiber filler loading necessary for percolation by an order of magnitude and increases the conductivity of the material by an order of magnitude by forming many parallel percolated branches in the network. This low loading required for high conductivity allows the material to maintain \u3c6% change in conductivity between the flat and bent (0.7 mm radius) states with no degradation over 500 cycles, due to the low particle loading and encapsulation of particle networks. Furthermore, using acoustic assembly during printing of these materials allows on-the-fly modulation between this conductive material and un-percolated insulating material during printing, with additional control over the anisotropy of the conductive network, all with the same nozzle and ink. This allows versatile design of integrated circuits in 3d printed soft components, as well as tuning of strain tolerance in multiple directions, without the cost and manufacturing limitations of lithography, or CNT growth steps, prestretch/burn-off steps, or liquid metal safety concerns. Acoustically patterned: \u3e5000 S/m @ 2.6v% Unpatterned: \u3c1500 S/m @ 13v% (a) Please click Additional Files below to see the full abstract

Controlling the dynamic percolation of carbon nanotube based conductive polymer composites by addition of secondary nanofillers: The effect on electrical conductivity and tuneable sensing behaviour

In this paper, the electrical properties of ternary nanocomposites based on thermoplastic polyurethane (TPU) and multi-walled carbon nanotubes (MWCNTs) are studied. In particular two nanofillers - differing in shape and electrical properties - are used in conjunction with MWCNTs: an electrically conductive CB and an insulating needle-like nanoclay, sepiolite. The ternary nanocomposites were manufactured in a number of forms (extruded pellets, filaments and compression moulded films) and their morphological and electrical properties characterised as function of time and temperature. The presence of both secondary nanofillers is found to affect the formation of a percolating network of MWCNTs in TPU, inducing a reduced percolation threshold and tuneable strain sensing ability. These ternary nanocomposites can find application as conductive and multi-functional materials for flexible electronics, sensing films and fibres in smart textiles. (c) 2012 Elsevier Ltd. All rights reserved

Novel Multifunctional Materials Based on Oxide Thin Films and Artificial Heteroepitaxial Multilayers

Transition metal oxides show fascinating physical properties such as high temperature superconductivity, ferro- and antiferromagnetism, ferroelectricity or even multiferroicity. The enormous progress in oxide thin film technology allows us to integrate these materials with semiconducting, normal conducting, dielectric or non-linear optical oxides in complex oxide heterostructures, providing the basis for novel multi-functional materials and various device applications. Here, we report on the combination of ferromagnetic, semiconducting, metallic, and dielectric materials properties in thin films and artificial heterostructures using laser molecular beam epitaxy. We discuss the fabrication and characterization of oxide-based ferromagnetic tunnel junctions, transition metal-doped semiconductors, intrinsic multiferroics, and artificial ferroelectric/ferromagetic heterostructures - the latter allow for the detailed study of strain effects, forming the basis of spin-mechanics. For characterization we use X-ray diffraction, SQUID magnetometry, magnetotransport measurements, and advanced methods of transmission electron microscopy with the goal to correlate macroscopic physical properties with the microstructure of the thin films and heterostructures.Comment: 21 pages, 21 figures (2 figures added, typos corrected

Nanoarchitectonics of metal oxide materials for sustainable technologies and environmental applications

Sustainable development compliant with environment and human health protection motivates researchers to explore green solutions towards improved economic and social wellbeing. These objectives, still very far from being achieved especially in developing countries, must necessarily be pursued through the tailored fabrication of low-cost, eco-friendly, efficient and stable multi-functional materials. In particular, nanostructures based on first-row transition metal oxides are amenable candidates for clean energy production, air purification and self-cleaning/anti-fogging purposes, especially if obtained through fabrication strategies allowing a careful modulation of their characteristics. In this highlight, after a brief introduction of the above issues, we provide selected representative examples of green oxide-based nanoarchitectures for the targeted end-uses. Attention is focused on the interplay between the material chemico-physical properties and the resulting functional performances, with the aim of providing some hints to control material behavior by design. In addition, we provide a critical outlook not only on the unique opportunities, but also on the main open challenges related to the use of the above multi-functional materials, in an attempt to stimulate further advancements in these emerging research areas

Interlaminar bonding in ultrasonic consolidation

Ultrasonic Consolidation (UC) is a solid state additive manufacturing process which fabricates three-dimensional objects by ultrasonically joining metal foils together, layer-bylayer, to form a solid part. A wide range of materials can be used to fabricate parts by UC and products with complex internal geometry can be generated by shaping the crosssection throughout the build using Computer Numerically Controlled (CNC) milling. As a result of its ability to embed various secondary materials and fibres in metal matrices, UC has emerged as a potential method of fabricating multi-functional materials and structures. [Continues.