LAB REPORT

Diamond stands up to a squeeze. Surprisingly, the material’s structure persists even when compressed to 2 trillion pascals, more than five times the pressure in Earth’s core, Lawrence Livermore scientists recently reported.

The study suggests that diamond is metastable at high pressures: It retains its structure even though other, more stable structures are expected to dominate under such conditions. Studying diamond’s quirks at extreme pressures could help reveal the inner workings of carbon-rich exoplanets.

Diamond is one of several varieties of carbon, each composed of a different arrangement of atoms. At everyday pressures on Earth’s surface, carbon’s most stable state is graphite. But given a forceful squeeze, diamond wins out. That’s why diamonds form after carbon takes a plunge inside Earth.

But at higher pressures than those found inside Earth, scientists had predicted that new crystal structures would be more stable. Physicist Amy Lazicki and colleagues pummeled diamond with powerful lasers at LLNL’s National Ignition Facility. X-ray measurements of the material’s structure revealed that diamond persisted, suggesting it is metastable under extreme pressure.

The first-ever shot to study a high explosive sample was recently conducted at the National Ignition Facility, the world’s most energetic laser. The results from the shot included novel data that will help researchers unlock the mysteries of high-explosive chemistry and position Lawrence Livermore to continue its legacy as a leader in HE science and diagnostic innovation.

“This shot is the first in a series that will transform the Lab’s understanding of high explosives by producing never-before-captured experimental data quantifying the response of laser-driven high explosives during reaction,” said Lara Leininger, director of LLNL’s Energetic Materials Center and lead for this Laboratory Directed Research and Development project.

The results also allow LLNL to critically evaluate predictive computational capabilities and the Lab’s world-class thermochemical code, Cheetah, and greatly expand experimental capabilities being applied in high explosives.

Some promising biosensors and medical devices work well within pristine laboratory environments. However, they tend to stop working to deliver medical therapeutics or monitor chronic health issues once exposed to the real-world conditions of complex biological fluids.

A thick layer of foulants will quickly cover biosensors, and there is no good way to revive them once they quit working. Essentially, a biosensor is only as good as its antifouling properties.

In the journal APL Materials, Aleksandr Noy and Xi Chen of Lawrence Livermore National Laboratory review a variety of approaches developed to combat fouling. These approaches encompass physical barriers, chemical treatments, nonstick surfaces and selective membranelike coatings that form "gates" to only allow certain species to reach a sensor's working surface.

"There is a whole universe of very clever and quite effective approaches to protect biosensors from fouling," Noy said. "Researchers have their pick of the technology they can tailor to the particular type of sensor they want to design."

LLNL researchers have discovered that carbon nanotube membrane pores could enable ultra-rapid dialysis processes that would greatly reduce treatment time for hemodialysis patients.

The ability to separate molecular constituents in complex solutions is crucial to many biological and man-made processes. One way is via the application of a concentration gradient across a porous membrane. This drives ions or molecules smaller than the pore diameters from one side of the membrane to the other while blocking anything that is too large to fit through the pores.

In nature, biological membranes such as those in the kidney or liver can perform complex filtrations while still maintaining high throughput. Synthetic membranes, however, often struggle with a well-known trade-off between selectivity and permeability. The same material properties that dictate what can and cannot pass through the membrane inevitably reduce the rate at which filtration can occur.

LLNL researchers found that carbon nanotube pores (graphite cylinders with diameters thousands of times smaller than a human hair) might provide a solution to the permeability vs. selectivity tradeoff.

Early planetary migration in the solar system has been long established, and there are myriad theories that have been put forward to explain where the planets were coming from. Theories such as the Grand Tack Hypothesis and the Nice Model show how important that migration is to the current state of our solar system. 

A team from Lawrence Livermore National Laboratory has come up with a novel way of trying to understand planetary migration patterns by looking at meteorite compositions.

The researchers had three key realizations. First, that almost all the meteorites that have fallen to Earth originated from the asteroid belt. Second, that the asteroid belt is known to have formed by sweeping material up from all over the solar system. And third, and perhaps most importantly, that they could analyze the isotopic signatures in meteorites to help determine where a given asteroid had formed in the solar system.  

Their analysis showed that the original location of the planets in our solar system aren’t exactly where they lie today.