HIGHLIGHTS
3D printing process (J. H. Martin et al; Nature, 2017, 549, 365). The authors used a laser or an
electron beam to melt alloy powders locally. The molten alloy solidified at rates of 0.1 to 5ms-1
, which is even
an order of magnitude faster than in a conventional casting process. To control solidification, small amounts of an additive in form of a nanoparticle grain refiner helped with the nucleation of the new alloy grains.
The alloys chosen were all based on aluminium and included other low-cost elements (Cu, Mg, Zn, Fe,
Scheme 3 Structure of a PIM Applied chemistry
NIGEL P FREESTONE University of Northampton, UK
Mirror that can be switched on and off Scientists at Imperial College London, UK, have created a reversible electrotunable liquid mirror based on voltage-controlled self-assembly/ disassembly of 16nm plasmonic nanoparticles at the interface between two immiscible electrolyte solutions (Y. Montelongo, D. Sikdar, Y. Ma, A. J. S. McIntosh, L. Velleman, A. R. Kucernak, J. B. Edel, A. A. Kornyshev; Nature Materials, 2017, 16, 1127). In order to tune the optical
properties of a single layer of nanoparticles, which are only tens of nanometres in size each, the space between them needs to be set precisely and uniformly. To form the layer, the researchers created conditions for gold nanoparticles to localise at the interface between two liquids that do not mix. By applying a small voltage across
the interface, the team has been able to demonstrate a tuneable nanoparticle layer that can be dense or sparse, allowing for switching between a reflective mirror and a transparent surface (Scheme 1). The distance between the
nanoparticles determines whether the layer permits or reflects different wavelengths of light. At one extreme, all the wavelengths are reflected, and the layer acts as a mirror. At the other extreme, when the nanoparticles are dispersed, all wavelengths are
permitted through the interface and it acts as a window. In contrast to previous nanoscopic systems that used chemical means to change the optical properties, the team’s electrical system is reversible. This study opens a route towards
realisation of such platforms in future micro/nanoscale electrochemical cells, enabling the creation of tunable plasmonic metamaterials.
Wax on, melt off Incorporating small quantities of phase change materials (PCMs), such as paraffin wax, into concrete using porous lightweight aggregate or embedded pipes in a road’s concrete mix can create roads that de-ice themselves during winter storms (Y. Farnam, H. S. Esmaeeli, P. D. Zavattieri, J. Haddock, J. Weiss; Cement and Concrete Composites, 2017, 84, 84). During cooling when the PCM
transforms from liquid to solid, it can release thermal heat that can be used to melt ice and snow. By inhibiting the formation of ice and snow on the pavement or
Mn, Ti, Si). They were used in powder form with typical particle sizes of
around 45µm. The additive consisted of hydrogen-stabilised zirconium, ZrH2
air but decomposed at the melting temperature, creating Al3
, particles, which were stable in Zr nucleants
with a crystallographic lattice spacing and density that matched the aluminium alloy. With their help, crack-free aluminium alloy samples with a strength similar to that of wrought alloy parts were successfully produced by 3D printing. The new technology could have an impact in aerospace, biomedical and automotive areas where high- strength alloys are highly sought.
bridge surface, the use of PCMs may reduce or eliminate the need for de-icing chemicals/salts, snowploughing or both, thus saving money and positively influencing the environmental impact of such operations.
Switchable open/closed polyaromatic macrocycle The macrocycle has a well-defined hydrophobic cavity around 1nm in length, surrounded by four pH- responsive acridinium panels. The cylindrical cavity can bind to long hydrophilic molecules in neutral water and then release them through an open-to-closed structural change upon addition of base. Incorporation of the macrocycles
into infinite polymer and inorganic matrixes, could provide novel stimuli- responsive sensing and separating materials.
Scheme 1 Depending on whether the device is in a window state or a mirror state, a £10 note or a £1 coin is visible, respectively
Smart graphene membrane to desalinate water Graphene-based desalination membranes that are more robust and scalable than current nanofiltration membrane technologies, have been developed (A. Morelos-Gomez, R. Cruz-Silva, H. Muramatsu, J. Ortiz- Medina, T. Araki, T. Fukuyo, S. Tejima,
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