FORWARD TO THE PAST

New chainmail-like material could be the future of armor

First 2D mechanically interlocked polymer exhibits exceptional flexibility and strength

Northwestern University

Facebook

XLinkedIWeChatBlueskyMessageWhatsAppEmail

 

image: 

This illustration shows how X-shaped monomers are interlinked to create the first 2D mechanically interlocked polymer. Similar to chainmail, the material exhibits exceptional strength.

view more 

Credit: Mark Seniw, Center for Regenerative Nanomedicine, Northwestern University

EVANSTON, Il. --- In a remarkable feat of chemistry, a Northwestern University-led research team has developed the first two-dimensional (2D) mechanically interlocked material.

Resembling the interlocking links in chainmail, the nanoscale material exhibits exceptional flexibility and strength. With further work, it holds promise for use in high-performance, light-weight body armor and other uses that demand lightweight, flexible and tough materials.

Publishing on Friday (Jan. 17) in the journal Science, the study marks several firsts for the field. Not only is it the first 2D mechanically interlocked polymer, but the novel material also contains 100 trillion mechanical bonds per 1 square centimeter — the highest density of mechanical bonds ever achieved. The researchers produced this material using a new, highly efficient and scalable polymerization process.

“We made a completely new polymer structure,” said Northwestern’s William Dichtel, the study’s corresponding author. “It’s similar to chainmail in that it cannot easily rip because each of the mechanical bonds has a bit of freedom to slide around. If you pull it, it can dissipate the applied force in multiple directions. And if you want to rip it apart, you would have to break it in many, many different places. We are continuing to explore its properties and will probably be studying it for years.”

Dichtel is the Robert L. Letsinger Professor of Chemistry at the Weinberg College of Arts and Sciences and a member of the International Institute of Nanotechnology (IIN) and the Paula M. Trienens Institute for Sustainability and Energy. Madison Bardot, a Ph.D. candidate in Dichtel’s laboratory and IIN Ryan Fellow, is the study’s first author.

Inventing a new process

For years, researchers have attempted to develop mechanically interlocked molecules with polymers but found it near impossible to coax polymers to form mechanical bonds. 

To overcome this challenge, Dichtel’s team took a whole new approach. They started with X-shaped monomers — which are the building blocks of polymers — and arranged them into a specific, highly ordered crystalline structure. Then, they reacted these crystals with another molecule to create bonds between the molecules within the crystal.

“I give a lot of credit to Madison because she came up with this concept for forming the mechanically interlocked polymer,” Dichtel said. “It was a high-risk, high-reward idea where we had to question our assumptions about what types of reactions are possible in molecular crystals.”

The resulting crystals comprise layers and layers of 2D interlocked polymer sheets. Within the polymer sheets, the ends of the X-shaped monomers are bonded to the ends of other X-shaped monomers. Then, more monomers are threaded through the gaps in between. Despite its rigid structure, the polymer is surprisingly flexible. Dichtel’s team also found that dissolving the polymer in solution caused the layers of interlocked monomers to peel off each other.

“After the polymer is formed, there’s not a whole lot holding the structure together,” Dichtel said. “So, when we put it in solvent, the crystal dissolves, but each 2D layer holds together. We can manipulate those individual sheets.” 

To examine the structure at the nanoscale, collaborators at Cornell University, led by Professor David Muller, used cutting-edge electron microscopy techniques. The images revealed the polymer’s high degree of crystallinity, confirmed its interlocked structure and indicated its high flexibility.

Dichtel’s team also found the new material can be produced in large quantities. Previous polymers containing mechanical bonds typically have been prepared in very small quantities using methods that are unlikely to be scalable. Dichtel’s team, on the other hand, made half a kilogram of their new material and assume even larger amounts are possible as their most promising applications emerge.

Adding strength to tough polymers

Inspired by the material’s inherent strength, Dichtel’s collaborators at Duke University, led by Professor Matthew Becker, added it to Ultem. In the same family as Kevlar, Ultem is an incredibly strong material that can withstand extreme temperatures as well as acidic and caustic chemicals. The researchers developed a composite material of 97.5% Ultem fiber and just 2.5% of the 2D polymer. That small percentage dramatically increased Ultem’s overall strength and toughness.

Dichtel envisions his group’s new polymer might have a future as a specialty material for light-weight body armor and ballistic fabrics.

“We have a lot more analysis to do, but we can tell that it improves the strength of these composite materials,” Dichtel said. “Almost every property we have measured has been exceptional in some way.”

Steeped in Northwestern history

The authors dedicated the paper to the memory of former Northwestern chemist Sir Fraser Stoddart, who introduced the concept of mechanical bonds in the 1980s. Ultimately, he elaborated these bonds into molecular machines that switch, rotate, contract and expand in controllable ways. Stoddart, who passed away last month, received the 2016 Nobel Prize in Chemistry for this work.

“Molecules don’t just thread themselves through each other on their own, so Fraser developed ingenious ways to template interlocked structures,” said Dichtel, who was a postdoctoral researcher in Stoddart’s lab at UCLA. “But even these methods have stopped short of being practical enough to use in big molecules like polymers. In our present work, the molecules are held firmly in place in a crystal, which templates the formation of a mechanical bond around each one.

“So, these mechanical bonds have deep tradition at Northwestern, and we are excited to explore their possibilities in ways that have not yet been possible.”

The study, “Mechanically interlocked two-dimensional polymers,” was primarily supported by the Defense Advanced Research Projects Agency (contract number HR00112320041) and Northwestern’s IIN (Ryan Fellows Program).

---

Journal

Science

DOI

10.1126/science.ads4968 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Mechanically interlocked two-dimensional polymers

Article Publication Date

17-Jan-2025

 

The megadroughts are upon us

Forty-year study: Extreme droughts will become more frequent, severe, and extensive

Institute of Science and Technology Austria

 

image: 

The Yeso reservoir in central Chile during a megadrought peak in Summer 2020.

view more 

Credit: © Vicente Melo Velasco | ISTA

Increasingly common since 1980, persistent multi-year droughts will continue to advance with the warming climate, warns a study from the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), with Professor Francesca Pellicciotti from the Institute of Science and Technology Austria (ISTA) participating. This publicly available forty-year global quantitative inventory, now published in Science, seeks to inform policy regarding the environmental impact of human-induced climate change. It also detected previously ‘overlooked’ events.

Fifteen years of a persistent, devastating megadrought—the longest lasting in a thousand years—have nearly dried out Chile’s water reserves, even affecting the country’s vital mining output. This is but one blatant example of how the warming climate is causing multi-year droughts and acute water crises in vulnerable regions around the globe. However, droughts tend only to be noticed when they damage agriculture or visibly affect forests. Thus, some pressing questions arise: Can we consistently identify extreme multi-year droughts and examine their impacts on ecosystems? And what can we learn from the drought patterns of the past forty years?

To answer these questions, researchers from the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL) and the Institute of Science and Technology Austria (ISTA) have analyzed global meteorological data and modeled droughts between 1980 and 2018. They demonstrated a worrying increase in multi-year droughts that became longer, more frequent, and more extreme, covering more land. “Each year since 1980, drought-stricken areas have spread by an additional fifty thousand square kilometers on average—that’s roughly the area of Slovakia, or the US states of Vermont and New Hampshire put together—, causing enormous damage to ecosystems, agriculture, and energy production,” says ISTA Professor Francesca Pellicciotti, the Principal Investigator of the WSL-funded EMERGE Project, under which the present study was conducted. The team aims to unveil the possible long-lasting effects of persistent droughts around the globe and help inform policy preparing for more frequent and severe future megadroughts.

Unveiling extreme droughts that flew under the radar

The international team used the CHELSA climate data prepared by WSL Senior Researcher and study author Dirk Karger, which goes back to 1979. They calculated anomalies in rainfall and evapotranspiration—water evaporation from soil and plants—and their impact on natural ecosystems worldwide. This allowed them to determine the occurrence of multi-year droughts both in well-studied and less accessible regions of the planet, especially in areas like tropical forests and the Andes, where little observational data is available. “Our method not only mapped well-documented droughts but also shed light on extreme droughts that flew under the radar, such as the one that affected the Congo rainforest from 2010 to 2018,” says Karger. This discrepancy is likely due to how forests in various climate regions respond to drought episodes. “While temperate grasslands have been most affected in the past forty years, boreal and tropical forests appeared to withstand drought more effectively and even displayed paradoxical effects during the onset of drought.” But how long can these forests resist the harsh blow of climate change?

Contrasting impacts on ecosystems

The persistently rising temperatures, extended droughts, and higher evapotranspiration ultimately lead to dryer and browner ecosystems, despite also causing heavier precipitation episodes. Thus, scientists can use satellite images to monitor the effect of drought by tracking changes in vegetation greenness over time. While this analysis works well for temperate grasslands, the changes in greenness cannot be tracked as easily over dense tropical forest canopies, leading to underestimated effects of drought in such areas. Thus, to ensure consistent results worldwide, the team developed a multistep analysis that better resolves the changes in high-leaf regions and ranked the droughts by their severity since 1980. Unsurprisingly, they showed that megadroughts had the highest immediate impact on temperate grasslands. ‘Hotspot’ regions included the western USA, central and eastern Mongolia, and particularly southeastern Australia, where the data overlapped with two well-documented multi-year ecological droughts. On the other hand, the team shed additional light on the paradoxical effects observed in the tropical and boreal forests. While tropical forests can offset the expected effects of drought as long as they have enough water reserves to buffer the decrease in rainfall, boreal forests and tundra react in their distinct way. It turns out that the warming climate extends the boreal growth season since vegetation growth in these regions is limited by lower temperatures rather than water availability.

Droughts evolve in time and space

The results show that the trend of intensifying megadroughts is clear: The team generated the first global—and globally consistent—picture of megadroughts and their impact on vegetation at high resolution. However, the long-term effects on the planet and its ecosystems remain largely unknown. Meanwhile, the data already agrees with the observed widely greening pan-Arctic. “But in the event of long-term extreme water shortages, trees in tropical and boreal regions can die, leading to long-lasting damage to these ecosystems. Especially, the boreal vegetation will likely take the longest to recover from such a climate disaster,” says Karger. Pellicciotti hopes the team’s result will help change our perception of droughts and how to prepare for them: “Currently, mitigation strategies largely consider droughts as yearly or seasonal events, which stands in stark contrast to the longer and more severe megadroughts we will face in the future,” she says. “We hope that the publicly available inventory of droughts we are putting out will help orient policymakers toward more realistic preparation and prevention measures.” As a glaciologist, Pellicciotti also seeks to examine the effects of megadroughts in the mountains and how glaciers can buffer them. She leads a collaborative project titled “MegaWat—Megadroughts in the Water Towers of Europe—From Process Understanding to Strategies for Management and Adaptation.”

-

Project and funding information
The present study was conducted within the scope of the EMERGE Project of the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL) with Professor Francesca Pellicciotti from the Institute of Science and Technology Austria (ISTA) serving as its Principal Investigator. The research was supported by funding from the Extreme Program of the WSL for the EMERGE project.

 

The Yeso reservoir in central Chile during a megadrought peak in Summer 2020.

Drone Video from Chile, 2017. The Upper Rio Yeso catchment: a tributary to the Maipo River which serves the Chilean capital, Santiago.

The Yeso region in Central Chile, visibly dry during a peak of the megadrought in the Summer of 2020Facebook

Credit

© Vicente Melo Velasco | ISTA

LinkedIWeChatBlueskyMessageWhatsAppEmail

 

Chile, 2017. The Upper Rio Yeso catchment: a tributary to the Maipo River which serves the Chilean capital, Santiago.

Credit

© Thomas Shaw | ISTA

Dead vines in the region around Los Andes in the western catchment area of Aconcagua, a region that has been particularly hard hit by the ongoing drought in Chile.

Credit

(c) Dirk Kager / WSL

Journal

Science

DOI

10.1126/science.ado4245 

Method of Research

Computational simulation/modeling

Subject of Research

Not applicable

Article Title

Global increase in the occurrence and impact of multiyear droughts

Article Publication Date

17-Jan-2025

 

Multiyear “megadroughts” becoming longer and more severe under climate change

Summary author: Walter Beckwith

American Association for the Advancement of Science (AAAS)

Severe droughts are becoming hotter, longer, and increasingly devastating to ecosystems as climate change accelerates, according to a new study, which reports that temperate grasslands, including in parts of the United States, are facing the worst effects. The findings provide a global quantitative understanding of multiyear droughts (MYDs) – prolonged events lasting years or decades – and offer a benchmark for understanding their global trends and impacts. As droughts become more frequent worldwide, the likelihood of MYDs rises, posing severe threats to both natural ecosystems and human systems. These events deplete soil moisture and reduce streamflow, potentially causing irreversible damage, with consequences that include widespread crop failures, increased tree mortality, diminished ecosystem productivity, and reduced water supplies. Recent MYDs, like the Western U.S. drought (2000–2018) and Chile's ongoing drought (since 2010), have drawn significant concern due to their devastating impacts. However, less prominent MYDs, with fewer perceived consequences, may have gone unnoticed, highlighting the need for comprehensive knowledge of their occurrence and effects. To address this need, Liangzhi Chen and colleagues mapped the global distribution of 13,176 MYDs from 1980 to 2018 using the standardized precipitation evapotranspiration index (SPEI), which measures drought severity based on the balance between precipitation and potential evaporative demand. Chen et al. also assessed these events’ impacts on vegetation through remotely sensed greenness data. The findings show that over the last 40 years, MYDs have occurred on nearly every continent and have become increasingly widespread, hotter, and drier, with global land affected by these events increasing by 49,279 ±14,771 square kilometers annually. What’s more, the authors report that the ecosystem impacts of MYDs varied significantly, with temperate grasslands exhibiting greater declines in greenness compared to subtropical and tropical forests. While grasslands demonstrated low resistance to drought, they often displayed rapid recovery following drought events, highlighting their unique resilience dynamics. In a related Perspective, David Hoover and William Smith discuss the study and its findings in greater detail.

---

Journal

Science

DOI

10.1126/science.ado4245 

Article Title

Global increase in the occurrence and impact of multiyear droughts

Article Publication Date

17-Jan-2025

 

NASA scientists find new human-caused shifts in global water cycle

NASA/Goddard Space Flight Center

Facebook

XLinkedInWeChatBlueskyMessageWhatsAppEmail

 

image: 

Cracked mud and salt on the valley floor in Death Valley National Park in California can become a reflective pool after rains. 

view more 

Credit: NPS/Kurt Moses

In a recently published paper, NASA scientists use nearly 20 years of observations to show that the global water cycle is shifting in unprecedented ways. The majority of those shifts are driven by activities such as agriculture and could have impacts on ecosystems and water management, especially in certain regions.

“We established with data assimilation that human intervention in the global water cycle is more significant than we thought,” said Sujay Kumar, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a co-author of the paper published in the Proceedings of the National Academy of Sciences.

The shifts have implications for people all over the world. Water management practices, such as designing infrastructure for floods or developing drought indicators for early warning systems, are often based on assumptions that the water cycle fluctuates only within a certain range, said Wanshu Nie, a research scientist at NASA Goddard and lead author of the paper.

“This may no longer hold true for some regions,” Nie said. “We hope that this research will serve as a guide map for improving how we assess water resources variability and plan for sustainable resource management, especially in areas where these changes are most significant.”

One example of the human impacts on the water cycle is in North China, which is experiencing an ongoing drought. But vegetation in many areas continues to thrive, partially because producers continue to irrigate their land by pumping more water from groundwater storage, Kumar said. Such interrelated human interventions often lead to complex effects on other water cycle variables, such as evapotranspiration and runoff.

Nie and her colleagues focused on three different kinds of shifts or changes in the cycle: first, a trend, such as a decrease in water in a groundwater reservoir; second, a shift in seasonality, like the typical growing season starting earlier in the year, or an earlier snowmelt; and third a change in extreme events, like “100-year floods” happening more frequently.

The scientists gathered remote sensing data from 2003 to 2020 from several different NASA satellite sources: the Global Precipitation Measurement mission satellite for precipitation data, a soil moisture dataset from the European Space Agency’s Climate Change Initiative, and the Gravity Recovery and Climate Experiment satellites for terrestrial water storage data. They also used products from the Moderate Resolution Imaging Spectroradiometer satellite instrument to provide information on vegetation health.

“This paper combines several years of our team’s effort in developing capabilities on satellite data analysis, allowing us to precisely simulate continental water fluxes and storages across the planet,” said Augusto Getirana, a research scientist at NASA Goddard and a co-author of the paper.

The study results suggest that Earth system models used to simulate the future global water cycle should evolve to integrate the ongoing effects of human activities. With more data and improved models, producers and water resource managers could understand and effectively plan for what the “new normal” of their local water situation looks like, Nie said.

---

Journal

Proceedings of the National Academy of Sciences

Article Title

Nonstationarity in the global terrestrial water cycle and its interlinkages in the Anthropocene

 

Pacific Islander teens assert identity through language

Pacific Islanders at a more diverse school in Utah pronounced vowels subtly differently than students in a predominantly white school, in line with the theory that groups differentiate along ethnic lines where more groups share social space

University of Utah

 

video: 

Audio clips of study participants saying words from the wordlist. The words show the variation you might hear along a continuum from the location of the tongue in the mouth, from the higher vowel (HID) and the middle (HEAD).

view more 

Credit: Lisa Johnson and Lisa Potter

The kids and grandkids of immigrants to the United States usually lose the ability to speak their heritage language fluently. Without access to the heritage language, second- and third-generation Americans may use distinct words and pronunciations in the dominant language, English, to assert their ethnic identities and connect to their communities.

Sociolinguists have long viewed these shifts as markers of cultural change. Like differences in food, clothing and religion, differences in language are subtle ways that groups distinguish themselves along ethnic boundaries. Recent work has pivoted from asking what are the differences to why are there differences? How are they using language to carve out identity? What is the local context that influences how people speak?

One theory posits that ethnic markers are prevalent when two or more cultural groups interact. A recent study led by University of Utah and Brigham Young University researchers is the first to directly test it in the real world. The linguists compared how white and Pacific Islander teens pronounced a series of English words in two Utah high schools with different ethnic makeups: One with a predominately white student body and the other with a lack of an ethnic majority. They found greater phonetic markers among students at the school with more diversity, indicating that the ethnic boundaries are more prominent in that setting.

“Part of identity comes from not just who you’re like, but who you’re different from,” said lead author Lisa Johnson. Now an assistant professor of linguistics at Brigham Young University (BYU), she collected the data as an anthropology doctoral student at the U. “Adolescence is a time when youth gain the cognitive ability and social desire to separate themselves from their parents and find their place in the wider world. In that way, adolescent social structures are like a microcosm of the larger society.”

The paper published in Human Nature on Oct. 21, 2024.

Language shifts as subtle signals

Establishing identity is a deeply human experience. Scholars attribute our success as a species to the ability to form coalitions and cooperate. Over time, we’ve developed conscious and unconscious signals to organize ourselves into groups. These signals include subtle differences in pronunciation, which we may not be conscious of. 

Sociolinguistic research in the U.S. has generally ignored Pacific Islanders, a group with deep roots in the west, especially Utah. Pacific Islanders first came to Utah in the late 1800s when Native Hawaiians migrated to the state after contact by The Church of Jesus Christ of Latter-day Saints missionaries. In the 60s, a new wave of people from the Samoa and the Kingdom of Tonga settled in the Wasatch Front, followed by more recent migrations of Fijian, Marshallese, Micronesian and other groups from around the Pacific Rim. Despite different origins, customs and languages, Pacific Islanders have a strong desire to court common values such as religion and a strong sense of responsibility to your family and surrounding community, said Adrian Bell, anthropologist at the U and co-author of the study.

“This study highlights the processes that influence language shifts and what helps preserve the culture. The older generations of Pacific Islanders really care that their grandchildren will reflect some of what they grew up with in their heritage country,” said Bell, whose mother was among the early Tongan immigrants who arrived in the 1970s. “The PI group isn’t necessarily large, but it’s very visible. Part of it is how we see ourselves, and another part is how others see us.”

Speaking with tongues

One way of marking identity is with subtle variations in vowel pronunciation. Vowels are all about the tongue’s location in the mouth; when speaking a vowel, the tongue can be positioned on a scale from high to low and front to back. For example, say the words bit, bet and bat—notice how your tongue moves lower and farther back?

“By varying tongue positions, speakers in every variety of English are engaged in systematic changes in the pronunciation of vowels, called ‘vowel shifts,’ that serve to differentiate one dialect from another,” explained Marianna Di Paolo, sociolinguist at the U and co-author of the paper, who served as Johnson’s U’s faculty advisor. 

This study focused on a series of recent vowel changes called the “California Shift,” a phenomenon mocked in the Saturday Night Live skit, “The Californias”—think “trahp” instead of “trap.” Try it—your tongue gets lower and moves farther back in the mouth.

The researchers chose 130 words with different vowels in a variety of word contexts. Participants spoke each word as they flashed across a computer screen in random order, displaying each word twice. Using audio software, the authors analyzed the resonant frequencies of speakers’ vowels to identify the subtle differences pronunciation.

They found strong evidence of ethnic markers at the diverse school. For example, there was a big difference in how students said words like “bit” or “kit.”  The Pacific Islanders said this vowel using the more traditional pronunciation with the tongue in a high, front position. In contrast, the white students were much more likely to use the California Shift pronunciation, lowering and shifting the tongue backwards so that “bit” sounded more like “bet.” Surprisingly, this difference was not observed at the predominately white school. In other words, there was a stronger tendency for groups to differentiate where more groups shared the same social space.

“In my mind, that's an indication of a growing awareness of diversity as the demographics of the state are changing,” Johnson said. “This is happening in Utah right now. It’s interesting to see how we’re grappling with those changes, not just in how we mark different groups, but also in how we relate to each other.”

The study serves as a snapshot at two different points of progress—people in the suburbs have more diversity than before, but not as much diversity as the more urban school. The authors hope other researchers can apply this new framework to show how a person’s cultural identity is influenced by the context in which they grow up. 

“The bigger picture around ethnic marker theory is to understand what drives cultural change and what helps preserve aspects of culture itself,” Bell said. “Right now, we’re seeing some Pacific Islanders form a kind of Polynesian pan-ethnic identity, probably also happening among our Micronesian and Melanesian relatives, using shared words to build a larger community around shared values.”

The paper, “Evidence for greater marking along ethnic boundaries,” published Oct. 21, 2024, in the journal Human Nature. The research was funded by the National Science Foundation under grant # 1749582.

---

Journal

Human Nature

DOI

10.1007/s12110-024-09479-1 

Method of Research

Experimental study

Subject of Research

People

Article Title

Evidence for greater marking along ethnic boundaries