Lawrence Livermore National Laboratory



Additive Manufacturing Promotes Material “Origami”

A team of Livermore researchers has demonstrated three-dimensional (3D) printing of shape-shifting structures that can fold or unfold to reshape themselves when exposed to heat or electricity. An article published in the June 15, 2016, issue of Scientific Reports describes the fabrication of micro-architected structures—boxes, spirals, and spheres—from a conductive, environmentally responsive polymer ink developed at the Laboratory. Although using responsive materials in 3D printing, often known as four-dimensional (4D) printing, is not new, Livermore researchers are the first to combine 3D printing and subsequent origami folding with conductive smart composite materials to build complex structures.

In the paper, the researchers describe creating primary shapes from an ink made from soybean oil, additional copolymers, and carbon nanofibers, and “programming” a temporary shape at a specific temperature. Next, shape-morphing was induced with ambient heat or an electrical current, which reverts the part from its temporary shape back to its original shape.

Lead author and Livermore postdoctoral reasearcher Jennifer Rodriguez explains, “We take the part out of the oven before it’s done and set the permanent structure of the part by folding or twisting after an initial gelling of the polymer.” Ultimately, Rodriguez says, researchers can use the materials to create extremely complex parts. “If we printed a part out of multiple versions of these formulations, with different transition temperatures, and ran it through a heating ramp, they would expand in a segmented fashion and unpack into something much more complex.”
Contact: Jennifer Rodriguez (925) 422-4266 (rodriguez96@llnl.gov).

Platform Measures Cell Response

For the first time, Lawrence Livermore researchers have successfully incorporated adult human peripheral nervous system cells on a microelectrode platform for long-term testing of chemical and toxic effects on cell health and function. The study, part of a project known as iCHIP (in vitro chip-based human investigational platform), was recently published in the June 28, 2016, online issue of the journal Analyst. The paper describes the integration of primary human dorsal root ganglia (DRG) cells and glial cells onto a microfluidics chip with embedded electrodes and the successful testing of several chemicals on the living cells over a period of up to 23 days.

Ultimately, scientists say the research will provide a noninvasive testing platform outside the human body that will predict human exposure to drugs and toxins more accurately than animal studies. “It’s a platform for testing low-level chronic exposure to chemicals and for therapeutic drug screening and testing of environmental contaminants in cases where we can’t test directly in humans,” says the paper’s lead author, Livermore scientist Heather Enright. “iChip provides a way to get human-relevant data without using animals, especially since those results don’t always extrapolate to humans.”

During the study, the team repeatedly exposed human DRG neurons and glial cells to capsaicin, a chemical found in chili peppers, ATP (a neuron receptor activator), and potassium chloride. The neural responses to the chemicals were recorded and compared to other reports of similar interactions found in the scientific literature. iCHIP principal investigator Elizabeth Wheeler said the team will continue to recapitulate different tissues of the body to better understand pain mechanisms and other cell–chemical interactions.
Contact: Elizabeth Wheeler (925) 423-6245 (wheeler16@llnl.gov).

Team Tracks Core of Massive Object in Universe

The Perseus cluster is a group of galaxies in the constellation Perseus (see image at left) and is one of the most massive objects in the known universe, containing thousands of galaxies immersed in a vast cloud of multimillion-degree gas. The Hitomi collaboration, in which Lawrence Livermore scientist Greg Brown is a member, found that the turbulent motion of the intracluster gas in the Perseus cluster is only a small fraction of the mechanism responsible for heating the gas to 50 million kelvins.

This finding, published in the July 6, 2016, edition of Nature, demonstrates that an accurate mass of a cluster can be inferred almost exclusively from its thermal hydrostatic pressure without having to rely on low-accuracy measurements and estimates of the turbulent pressure of the system. Accurate cluster masses provide strong constraints on cluster cosmology and dark matter.

This recent discovery is the result of measurements taken with the Soft X-ray Spectrometer (SXS), which was flown on the Hitomi X-ray Observatory and designed and built at NASA’s Goddard Space Flight Center. The high-energy resolution of the SXS made it possible, for the first time, to measure a high-resolution, high-throughput spectrum of a cluster of galaxies. Brown says, “The high-resolution of the SXS has revolutionized our view of some of the largest, most energetic objects in the universe.”
Contact: Greg Brown (925) 422-6879 (brown86@llnl.gov).

Ultralightweight and Flexible Metallic Materials

Livermore engineers, scientists, and academic partners, which include Virginia Polytechnic Insititute and State University (Virginia Tech) and the Massachussetts Institute of Technology (MIT), have achieved unprecedented scalability in printing three-dimensional (3D) architectures of arbitrary geometry, opening the door to super-strong, ultralightweight, and flexible metallic materials for aerospace, military, and automotive applications. In a study published in the July 18, 2016, online issue of Nature Materials (and susequently featured on the cover of the journal’s October issue) the team reported fabricating multiple layers of fractal-like lattices with features ranging from the nanometer to centimeter scale. This work resulted in a nickel-plated mechanical metamaterial with a higher than expected tensile elasticity.

According to lead author Xiaoyu “Rayne” Zheng, a former Livermore technical staff member who is now professor of mechanical engineering at Virginia Tech, “These nanoscale 3D features have some really interesting properties, but people have never been able to scale them up and see how they behave. We’ve figured out a strategy of hierarchically building them to take advantage of the nanoscale features at a large scale.”

The lattices were initially printed out of polymer, using a one-of-a-kind large-area projection microstereolithography printer invented by Livermore engineer Bryan Moran, who won an R&D 100 Award in 2015 for the design. The lattice structure was then coated with a nickel–phosphorus alloy and put through postprocessing to remove the polymer core, leaving extremely lightweight, hollow tube structures. Chris Spadaccini, director of the Laboratory’s Center for Engineered Materials and Manufacturing, says, “Using the structural concept of unit cells and lattices, combined with nanoscale features, we can achieve high strength at a very light weight, as well as a ductile-like behavior in materials that are normally brittle.”
Contact: Chris Spadaccini (925) 423-3185 (spadaccini2@llnl.gov).

Pulsed Ion Beams Probe Radiation Defects

Materials scientists at Lawrence Livermore, along with colleagues at Texas A&M University, have developed a novel experimental method to access the dynamic regime of radiation damage that occurs in nuclear and electronic materials. The new approach uses pulsed ion beams to measure defect lifetimes, interaction rates, and diffusion lengths. Because of the complexity involved, a full predictive capability of radiation damage still does not exist even for the simplest and best studied materials, and understanding mechanisms of dynamic radiation damage formation in solids remains a major materials physics challenge.

In a paper published in the August 3, 2016, edition of Scientific Reports, the team describes how they addressed this challenge using pulsed-ion-beam measurements of the dynamics of defect interaction in silicon carbide, a prototypical nuclear ceramic and wide-band-gap semiconductor. The team found that in the material, the dominant defect relaxation processes occur on millisecond timescales, and that the defect lifetime exhibits a non-monotonic temperature dependence.

“The pulsed-beam method allowed us to access the dynamic regime of radiation damage formation, which is essential for predicting the material behavior in different radiation environments,” says Livermore materials scientist L. Bimo Bayu Aji, the lead author of the paper. Laboratory scientist Joseph Wallace summarizes, “The understanding of radiation defect dynamics may suggest new paths to designing radiation-resistant materials.” Livermore project lead Sergei Kucheyev adds, “The understanding of defect interaction dynamics, probed in our pulsed-beam experiments, also is essential for using laboratory findings for predicting the material behavior under irradiation over timescale relevant to nuclear material service.”
Contact: Sergei Kucheyev (925) 422-5866 (kucheyev1@llnl.gov).

De-icing Agent Remains Stable Under Extreme Pressure

Lawrence Livermore scientists have overturned established assumptions about the high-pressure structural behavior of magnesium chloride (MgCl2), an effective de-icing agent used in aviation. The Livermore team observed MgCl2 to be extensively stable under pressure, in contradiction to previously well-established structural systematics. The work, published in the August 12, 2016, edition of Scientific Reports, sought to provide equations of state (EOS) and structural phase diagrams to improve the confidence of semi-empirical thermochemical calculations predicting the products and performance of detonated chemical formulations.

“To determine accurate EOS data, we first conducted high-pressure x-ray diffraction measurements up to 40 gigapascals (GPa), or 400,000 times atmospheric pressure,” says Joe Zaug, a Livermore physical chemist and the project leader. “According to previous theoretical studies and the well-established phase diagram of high-pressure compounds,” adds lead author and Livermore physicist Elissaios Stavrou, “MgCl2 should have transformed to a higher coordination number [more dense] and a three-dimensionally connectivity structure well below 40 GPa.” However, MgCl2 remained in a low-coordination layered structure, even after crossing the 1-megabar (1 million atmospheres) pressure limit.
Contact: Joe Zaug (925) 423-4428 (zaug1@llnl.gov).