When it comes to the various nanowidgets scientists are developing, nanotubes are especially intriguing. That’s because hollow tubes that have diameters of only a few billionths of a meter have the potential to be incredibly useful, from delivering cancer-fighting drugs inside cells to desalinating seawater.
But building nanostructures is difficult. And creating a large quantity of nanostructures with the same trait, such as millions of nanotubes with identical diameters, is even more difficult. This kind of precision manufacturing is needed to create the nanotechnologies of tomorrow.
Help could be on the way. As reported online this week in the journal Proceedings of the National Academy of Sciences, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have discovered a family of nature-inspired polymers that, when placed in water, spontaneously assemble into hollow crystalline nanotubes. What’s more, the nanotubes can be tuned to all have the same diameter of between five and ten nanometers, depending on the length of the polymer chain.
The polymers have two chemically distinct blocks that are the same size and shape. The scientists learned these blocks act like molecular tiles that form rings, which stack together to form nanotubes up to 100 nanometers long, all with the same diameter.
“This points to a new way we can use synthetic polymers to create complex nanostructures in a very precise way,” says Ron Zuckermann, who directs the Biological Nanostructures Facility in Berkeley Lab’s Molecular Foundry, where much of this research was conducted.
Several other Berkeley Lab scientists contributed to this research, including Nitash Balsara of the Materials Sciences Division and Ken Downing of the Molecular Biophysics and Integrated Bioimaging Division.
“Creating uniform structures in high yield is a goal in nanotechnology,” adds Zuckermann. “For example, if you can control the diameter of nanotubes, and the chemical groups exposed in their interior, then you can control what goes through—which could lead to new filtration and desalination technologies, to name a few examples.”
The research is the latest in the effort to build nanostructures that approach the complexity and function of nature’s proteins, but are made of durable materials. In this work, the Berkeley Lab scientists studied a polymer that is a member of the peptoid family. Peptoids are rugged synthetic polymers that mimic peptides, which nature uses to form proteins. They can be tuned at the atomic scale to carry out specific functions.
For the past several years, the scientists have studied a particular type of peptoid, called a diblock copolypeptoid, because it binds with lithium ions and could be used as a battery electrolyte. Along the way, they serendipitously found the compounds form nanotubes in water. How exactly these nanotubes form has yet to be determined, but this latest research sheds light on their structure, and hints at a new design principle that could be used to build nanotubes and other complex nanostructures.
Diblock copolypeptoids are composed of two peptoid blocks, one that’s hydrophobic one that’s hydrophilic. The scientists discovered both blocks crystallize when they meet in water, and form rings consisting of two to three individual peptoids. The rings then form hollow nanotubes.
Cryo-electron microscopy imaging of 50 of the nanotubes showed the diameter of each tube is highly uniform along its length, as well as from tube to tube. This analysis also revealed a striped pattern across the width of the nanotubes, which indicates the rings stack together to form tubes, and rules out other packing arrangements. In addition, the peptoids are thought to arrange themselves in a brick-like pattern, with hydrophobic blocks lining up with other hydrophobic blocks, and the same for hydrophilic blocks.
“Images of the tubes captured by electron microscopy were essential for establishing the presence of this unusual structure,” says Balsara. “The formation of tubular structures with a hydrophobic core is common for synthetic polymers dispersed in water, so we were quite surprised to see the formation of hollow tubes without a hydrophobic core.”
X-ray scattering analyses conducted at beamline 7.3.3 of the Advanced Light Source revealed even more about the nanotubes’ structure. For example, it showed that one of the peptoid blocks, which is usually amorphous, is actually crystalline.
Remarkably, the nanotubes assemble themselves without the usual nano-construction aids, such as electrostatic interactions or hydrogen bond networks.
“You wouldn’t expect something as intricate as this could be created without these crutches,” says Zuckermann. “But it turns out the chemical interactions that hold the nanotubes together are very simple. What’s special here is that the two peptoid blocks are chemically distinct, yet almost exactly the same size, which allows the chains to pack together in a very regular way. These insights could help us design useful nanotubes and other structures that are rugged and tunable—and which have uniform structures.”
The Advanced Light Source and the Molecular Foundry are DOE Office of Science User Facilities located at Berkeley Lab.
The research was supported by the Department of Energy’s Office of Science.
Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
- The article, “Self-assembly of crystalline nanotubes from monodisperse amphiphilic diblock copolypeptoid tiles,” was published in the PNAS Online Early Edition the week of March 28, 2016.
|The lithium-ion batteries that mobilize our electronic devices need to be improved if they are to power electric vehicles or store electrical energy for the grid. Berkeley Lab researchers looking for a better understanding of liquid electrolyte may have found a pathway forward. A team led by Richard Saykally, a chemist with Berkeley Lab’s Chemical Sciences Division, David Prendergast, a theorist with Berkeley Lab’s Molecular Foundry, and Steven Harris, a chemist with the Lab’s Materials Sciences Division, found surprising results in the first X-ray absorption spectroscopy study of a model lithium electrolyte (“X-Ray absorption spectroscopy of LiBF4 in propylene carbonate: a model lithium ion battery electrolyte”).|
|X-ray absorption spectra, interpreted using first-principles electronic structure calculations, provide insight into the solvation of the lithium ion in propylene carbonate. (Image courtesy of Rich Saykally, Berkeley)|
|“A crucial process in lithium ion batteries is the transport of lithium ions between the electrodes,” explains Saykally. “Commercial lithium-ion batteries contain a liquid electrolyte comprising a lithium salt dissolved in an alkyl carbonate solvent system. There’s disagreement in the battery industry on the nature of the local solvation environment of lithium ions in these solutions, a critical issue because the desolvation of the ions as they move through the negative electrode is believed to limit the electrical power that can be made available.”|
|Most previous computational simulations have predicted a tetrahedral solvation structure for the lithium ion in the electrolyte, but the new study by Saykally, Prendergast, Harris and their collaborators show this to not be the case.|
|“Our results indicate a solvation number of 4.5, which points to a non-tetrahedral solvation structure for the lithium ions,” says lithium-battery expert Harris. “This contradicts numerous theoretical studies which indicated a primarily tetrahedral coordination structure with a solvation number near 2 or 3, depending on the prevalence of ion pairing. Based on our results, to design better performing electrolytes, future computational models will need to move beyond tetrahedral coordination structures.”|
|Lithium-ion batteries (LIBs) make any short list of great inventions of the 20th century. Today LIBs represent a multibillion dollar industry as the power supply of cellular phones, tablets, laptops and other handheld electronic devices. However, serious shortcomings – high costs, inadequate energy densities, long recharge times and short cycle-life times – have hampered the use of LIBS for electric vehicles and for efficient electrical energy storage systems that can be used in conjunction with wind and solar energy sources.|
|Although it has become increasingly clear to the battery industry that improvements in the liquid electrolyte are essential if LIBs are to be effective for electric vehicles and large-scale energy storage, most LIB research has focused on the electrodes and solid electrolyte interphase. The problem has been a lack of capabilities for the requisite experiments, particularly X-ray spectroscopy.|
|This deficiency was addressed by Saykally and his group with their development of a unique liquid microjet technology in which two aqueous samples rapidly mix and flow through a finely tipped silica nozzle only a few micrometers in diameter. The resulting liquid beam travels a few centimeters in a vacuum chamber before it is intersected by an X-ray beam then collected and condensed out. This liquid microjet system has been set up at Beamline 8.0.1 of Berkeley Lab’s Advanced Light Source (ALS). Beamline 8.0.1 is a high flux undulator beamline that produces X-ray beams optimized for X-ray spectroscopy.|
|“Working at the ALS with our liquid microjet system, we used X-ray absorption spectroscopy to study lithium tetrafluoroborate in propylene carbonate,” Saykally says. “X-ray absorption spectroscopy is an atom-specific core-level spectroscopic probe of unoccupied electronic states. It is highly sensitive to both the intra- and intermolecular environment of the target atom.”|
|The XAS experimental spectra were interpreted through molecular dynamics and density functional theory spectral simulations carried out on the supercomputers at the National Energy Research Scientific Computing Center (NERSC) by Prendergast and Jacob Smith, a graduate student in Saykally’s research group. The ALS, the Molecular Foundry and NERSC are all DOE Office of Science national user facilities hosted at Berkeley Lab.|
|Source: By Lynn Yarris, Berkeley Lab|
Venkat Srinivasan, right, staff scientist in the Environmental Energy Technologies Division, talks about some of the new features as Project Director Richard C. Stanton listens in during a tour of the new General Purpose Laboratory at the Lawrence Berkeley Laboratory in Berkeley, Calif., on Tuesday, Oct. 28, 2014. The GPL, otherwise known as Building 33, is a new facility dedicated to pursuing research in energy storage and renewable energy. (Laura A. Oda/Bay Area News Group)
BERKELEY — Imagine an electric car with the range of a Tesla Model S — able to reach Lake Tahoe from the Bay Area on a single charge — but at one-fifth the $70,000 price tag for the luxury sedan.
Or a battery not only able to provide many times more energy than today’s technology but also at significantly cheaper prices, meaning longer-lasting and less expensive power for cellphones, laptops and even the home.
Those are among the ambitious goals of the $120 million, Department of Energy-funded Joint Center for Energy Storage Research, a 14-member partnership led by Argonne National Laboratory and including Lawrence Berkeley Lab, Sandia National Laboratories and a host of universities and private companies. In January, the center’s Berkeley hub is moving into the lab’s new $54 million General Purpose Laboratory, bringing its battery scientists, chemists and engineers together under one roof for the first time.
The team, headed by JCESR Deputy Director Venkat Srinivasan, aims to achieve revolutionary advances in battery performance — creating devices with up to five times the energy capacity of today’s batteries at one-fifth the cost by 2017.
To accomplish the feat, Srinivasan is looking to replace the current standard-bearer for rechargeable batteries — lithium-ion — with batteries made of cheaper, more durable materials, including magnesium, aluminum and calcium.
“We want to go beyond and find the next generation of technology,” Srinivasan said. “It’s clear to us that the batteries we have today are not meeting the needs.”
While private companies such as Tesla and Toyota are working to improve on lithium-ion technology, in the United States it’s the government labs that are trying to move technology to the next level.
“There’s a real opportunity for next-generation storage,” Crabtree said. “You have to make a big step forward. Lithium-ion will not be able to make that step. … You need a big program and a group effort to make it happen.”
Nearly two years into the project, Crabtree said, researchers have narrowed down a list of about 100 types of “beyond lithium-ion” batteries to a handful of promising concepts that are already in the prototype phase.
In order to reach the Obama administration’s goals of producing a quarter of all the nation’s electricity from solar and wind by 2025, and having 1 million all-electric vehicles on the road in the coming years, consumers will need cheaper batteries with a higher energy density, faster charging time and more range, said Lawrence Berkeley Lab’s Srinivasan. A battery costing $100 per kilowatt hour — three to five times cheaper than today’s technology — would make electric vehicles and renewable energy affordable to the masses.
“Energy storage is a linchpin of the future,” Srinivasan said. “Today’s batteries are kind of expensive. How do we get it to the point where the battery can pay for itself? That’s the target we’re shooting for.”
Sharing the new state-of-the-art General Purpose Laboratory will be JCESR principal investigator and Lawrence Berkeley staff scientist Brett Helms, who is focusing his research on flow batteries, a type of large-scale rechargeable battery that stores energy in a liquid solution of electrolytes that can be pumped through a membrane, generating power when they circulate and react with electrodes.
Helms wants to use more cost-effective materials such as sulfur — a plentiful byproduct of refining crude oil — to create a battery with five to 10 times more energy than current flow batteries, at a much lower cost. Combined with solar panels and wind farms, massive high-density battery packs could store most of the energy generated for use at a later time, providing an uninterrupted power supply in homes day or night, rain or shine, allowing homeowners to go off-the-grid and access the energy at any time.
This would overcome one of the main problems with renewable systems: They can only produce energy when the conditions — sun or wind — are right, not necessarily when the energy is needed, as fossil fuel-fired generators do.
“We’re producing all of this energy, but where is it going to go and how is it going to be integrated into the grid?” Helms said. “The biggest concern is to take advantage of the investment we’ve been making in the renewables. If we don’t have an energy storage solution, we will have wasted that investment.”
Helms’ team is developing a membrane for the flow battery that would increase its durability and enable the battery to cycle, or charge, better. He aims to have a working prototype of a lithium-sulfur flow battery — the first of its kind — by the end of the five-year initiative. The technology, he said, could also someday power electric vehicles.
“We’ve done battery work in the past, but thinking about national problems with people all over the country is an amazing opportunity,” Helms said.
The future home of Berkeley’s battery research hub is next door to the Advanced Light Source building, where automaker Toyota has been researching magnesium-ion batteries.
Whereas lithium-ion batteries have a charge of +1, providing a single electron per electrical current, magnesium has a charge of +2.
“For the same weight, you can have twice the charge — you’re doubling the amount of capacity,” Srinivasan said. “That’s exciting.”
Using high-performance computing, Srinivasan’s team has whittled down the number of materials to a few that have sufficient energy capacity and can be classified as safe, cheaper and longer-lasting than lithium. Within the next year, Srinivasan hopes to have other new materials ready for testing, and optimized prototypes ready by 2017.
George Crabtree, director of JCESR at Argonne National Laboratory near Chicago, said the federal government is pursuing the research to dramatically transform the two areas that consume two-thirds of all the energy generated in the United States — transportation and the energy grid. If successful, Crabtree said, consumers would benefit with cheaper electric cars and less dependence on utility companies for power at home.