Science Concentrates 3-D PRINTING ENERGY STORAGE
▸ Spinning a triboelectric yarn
C R E D I T: ACS B I O M AT E R. S C I . EN G . ( MI CRO GRA P H S ) ; ACS N AN O ( T EXT I LES); A DA PT E D F RO M S CI . A DV. (M O DE LS )
To Georgia Tech’s Zhong Lin Wang, our daily fidgeting, or even tossing and turning in bed at night, is a possible source of renewable energy. Wang’s group has made yarn composed of fabric fibers wrapped around a 50-µm-diameter stainless steel thread that can be woven into brightly colored, washable textiles that generate energy from motion (ACS Nano 2017, DOI: 10.1021/ acsnano.7b07534). Sewn into clothing, the textiles could harvest enough energy from walking and everyday activities to charge
Common textile materials such as cotton and wool can be wrapped around a thin, conductive steel wire to make a powergenerating yarn. cell phones and wearable electronics. The yarn is powered by the triboelectric effect, in which static electricity builds up from the friction between two different materials. When the materials move close together, electrons jump from one to the other. When they move back apart, those electrons flow into either a capacitor to store the charge or a circuit to generate power. As the yarn is stretched and released, the outer layer of fabric fibers—made from polyester, cotton, silk, or wool—moves closer to the stainless steel core, then away again, generating a small electric current. The researchers report that a sock with a textile patch charged a capacitor to 1 V after about 19 seconds of walking. The yarn works at up to 90% humidity, so it can survive heavy sweating. It also withstood 120 cycles through a washing machine, but it’s line dry only.—KATHERINE BOURZAC,
special to C&EN
Print processing improves popular polymers Current fabrication methods limit poly(dimethylsiloxane) (PDMS)—a popular material for biomedical applications—to simple device geometries. Veli Ozbolat of Çukurova University, Ibrahim T. Ozbolat of Penn State, and coworkers have found that three-dimensional printing enables fabrication of more complex shapes and at the same time improves the mechanical and cell adhesion properties of PDMS devices compared with standard PDMS casting methods (ACS Biomater. Sci. Eng. 2017, DOI: 10.1021/acsbiomaterials.7b00646). The researchers blended two PDMS elastomers to make 3-D-printing Cells adhere better to inks with desired properties. They 3-D-printed PDMS then used those blends to print surfaces, without and cast various samples. The fibronectin (center) samples made by 3-D printing were and with fibronectin (bottom), than they stronger, stiffer, and less porous do to conventionally than the ones made by casting. cast PDMS surfaces The researchers also found that (top). cells adhere better to 3-D-printed PDMS devices than to ones made by casting and that coating the printed surface with the extracellular matrix protein fibronectin further improves cell adhesion. They additionally used infrared spectroscopy of the devices to show that printing doesn’t alter the surface chemistry, leading them to attribute the improved cell adhesion to surface roughness imparted by the printing process.—CELIA ARNAUD
COMPUTATIONAL CHEMISTRY
▸ Lowering the heat for splitting nitrogen The world relies on the Haber-Bosch process to reduce atmospheric nitrogen to ammonia to make fertilizer, pharmaceuticals, and other industrially important chemicals. But the process requires high temperature and thereby consumes a tremendous amount of energy—about 1% of the world’s electricity every year. A new light-activated catalyst could dramatically reduce the temperature needed to drive the reaction, according to computer simulations (Sci. Adv. 2017, DOI: 10.1126/sciadv.aao4710). John Mark P. Martirez and Emily A. Carter at Princeton University have proposed that a gold-molybdenum catalyst could split dinitrogen’s triple bond at room temperature using visible light. That dissociation step is the primary limit on the Haber-Bosch process’s reaction rate. Their catalyst relies on a phenomenon called surface plasmon
resonance, in which the valence electrons on a nanoparticle—made of molybdenum-doped gold in this case—oscillate in unison when excited by a photon. Harnessed correctly, that excitation energy could push the nitrogen dissociation reaction over its high activation energy barrier, Carter says. The researchers evaluated the dissociation reaction for nitrogen in different excited states that are accessible at gold nanoparticle plasmon frequencies (models shown). Their calculations suggest that the catalyst can lower the energy needed to split nitrogen by about 80 to 90%. Carter says plans are in the works to collaborate with Naomi Halas and Peter Nordlander of Rice University to test the predictions.—SAM
LEMONICK JANUARY 8, 2018 | CEN.ACS.ORG | C&EN
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