Soft Matter Matters

Soft matter pervades our lives. Not only does soft matter make up our bodies and our foods, but it’s also a category of materials that enable many of society’s machines and processes. For example, the rubber for our tires and plastics for, well, just about everything.

Despite its significance, the study of soft matter as a distinct field is still relatively new in academia. Typically, it is scattered across chemistry, biology, physics and engineering departments. This fragmentation persists even though a deeper understanding of the complex processes governing soft matter could lead to groundbreaking advancements in areas ranging from medicine to construction. As our world faces major sustainability challenges with solid waste, recyclable soft materials can become part of the solution.

Michael Rubinstein, the Aleksandar S. Vesic Distinguished Professor in the Thomas Lord Department of Engineering and Material Science (MEMS) at Duke University, has been on a nearly 30-year quest to elevate the position of soft matter studies as a whole and to make North Carolina’s Research Triangle a worldwide hub for soft matter research.

“This new discipline is coalescing because it’s a new way of looking at nature,” said Rubinstein, who also holds appointments in Duke’s Departments of Biomedical Engineering, Physics and Chemistry. “Engineering and science departments are just beginning to wake up and realize its importance.”

While progress has been made in fits and starts, his efforts are now coming to a head. This summer, the first-ever International Soft Matter Conference taking place in the Americas was hosted in Raleigh, NC, drawing experts from around the globe to discuss the still relatively young scientific field. But beyond this success, his efforts—along with those of his colleagues in Duke Engineering—have also attracted top young scholars to establish their careers in soft matter research at Duke.

What is Soft Matter?

Soft matter refers to materials that can be easily altered by thermal fluctuations or external forces. This broad category includes liquids, gels, polymers, foams and biological systems. Everyday examples of soft matter include milk and most of our food. Our own bodies are made up of soft matter as well as the shampoos and lotions we use on them. Other materials, such as rubber, clay and cement, also fall under this classification.

It’s not that soft matter or using external forces to change them itself is new—after all, humans started fermenting milk into yogurt around 5,000 B.C.—but studying them under one academic umbrella is.

The term “soft matter” was first coined in the 1970s by Madeleine Veyssié and gained prominence through Pierre-Giles de Gennes, who won the Nobel Prize in Physics in 1991 and promoted the term in his visionary Nobel Prize lecture. The problem with soft matter is that it hasn’t had its own academically defined field of study, even after de Gennes’ Nobel Prize. Material engineers, chemists, physicists and biologists study soft matter but often don’t exchange ideas and results with each other, leading researchers to wander in different directions to solve the same problems instead of coming together to determine the optimal path.

“A lot of that comes down to communication,” Rubinstein said. “Different areas of science use different terms to talk about the same things. It’s not unlike the parable of the Tower of Babylon, where people of the world lose the ability to speak the same language and cannot build a tower into the sky.”

Academics from different fields speak different scientific languages, making it nearly impossible for them to collaborate. “That hinders the ability to understand complex systems like the cell or structured materials,” Rubinstein said. ” We are now going through textbooks together to develop a common language with the goal of understanding and working together to learn each other’s approaches.”

Establishing Soft Matter in the Research Triangle

Rubinstein came to the Research Triangle in 1995, first to the University of North Carolina – Chapel Hill (UNC), where he joined the growing polymer program. There, he began discussions with Jan Genzer, the Culberson Distinguished Professor at North Carolina State University (NC State), to hold joint meetings between those two universities and Duke to see if they could collaborate on the topic. Maybe, they thought, they could even join forces to advance research with the combined knowledge of how soft materials work.

At first, Genzer did not think of Rubinstein as a soft matter scientist. “Michael was more of a polymer physicist, but as he got more involved in collaborations with people from different disciplines, he became one of the gurus of soft matter in the world,” Genzer said.

In 2009 Rubinstein and Genzer launched the Triangle Soft Matter Workshop (TMSW). “The TSMW is a one-day meeting to share results, ideas and different approaches to studying soft matter from the points of view of biology, chemistry, physics and chemical engineering,” Rubinstein said.

The meeting was a success and went on to rotate between Duke, NC State and UNC every year. It draws about 150 people, and collaborations have led to joint proposals that resulted in funding for projects that involved faculty from all three schools despite their athletic rivalries. NC State organized the 16^th TSMW in 2024, and Duke will host the 17^th TSMW in May 2025. 

“Encouraging interactions and collaborations between soft matter physicists, chemists, biologists and engineers from all over the world has been important to the Research Triangle scientists,” Rubinstein said. “It’s a very fast-growing discipline.” 

Mister (Soft Matter) Worldwide

Rubinstein is also leading efforts to expand soft matter conferences, associations and collaborations worldwide. In 2010, he attended the second International Soft Matter Conference (ISMC) in Europe with nearly 600 delegates. The success of the European ISMCs was inspiring, and he knew that researchers from other parts of the world would be interested in attending and organizing such meetings.

To pursue this goal, he organized a Working Group on Soft Matter at the International Union of Pure and Applied Physics (IUPAP) and launched the “Soft Matter Around the World in Three Years” series of ISMCs, which rotates between three regions: Europe and Africa, Asia and Oceania, and the Americas. The first meeting held outside of Europe was in Osaka, Japan in 2023.

Then, this summer, ISMC came to Raleigh, NC. The 8^th International Soft Matter Conference was the first such event in the Americas and was held at the end of July and beginning of August at the Raleigh Convention Center. It drew nearly 500 researchers from across the globe to the Research Triangle. 

Rubinstein hopes that the international conferences will continue to expand and include more researchers from South America and Africa, and perhaps, eventually, locations on those continents will be added to the regular rotation of host conference sites. 

“This discipline is a way of reconnecting science back together,” said Rubinstein. “Conferences like these are connecting scientists working in different subfields of soft matter all over the world, encouraging them to discuss their different views and approaches of various phenomena at the same meeting.”

In addition to the technical sessions and panel discussions at this year’s ISMC in Raleigh, two satellite events were organized by the Research Triangle’s soft matter scientists. The first, the Young Investigator Workshop held at NC State, was a specialized event aimed at building working relationships, exchanging research knowledge, and developing skills among early-career researchers and students in the field. The workshop covered a range of sub-areas within soft matter research, including active matter, biological systems, granular materials, colloidal systems and polymers.

The second, The Duke Soft Matter Day, featured guest speakers, poster sessions for students, breakout groups and laboratory tours, with participants including experts from Harvard University, UC Santa Barbara, Hokkaido University and the University of Toronto.

Establishing a Soft Matter Future at Duke

Bavand Keshavarz and Michela Geri, both assistant professors in Mechanical Engineering and Materials Science (MEMS) at Duke and key organizers of both the Young Investigator Workshop and the Duke Soft Matter Day, came to Duke in January 2024 because they saw the promise in being able to carry out soft matter research across disciplines, not just within materials science. Duke would be “the perfect place to explore and be able to find my own path in the soft matter community,” said Geri,who studies multi-phase materials and structured fluids, like particle and droplet suspensions. It was different from other engineering departments, where she felt she would have been slotted into one specific category, even though her research is much broader.

“Soft matter is not exclusive to one discipline,” said Keshavarz, who studies the dynamics of complex fluids in complex flows. “Interdisciplinary research is naturally happening at Duke. The structure and philosophy of research has been embedded into the overall organization of departments and how faculty work over the years.”

Amir (Hossein) Salahshoor, assistant professor in Duke’s Departments of Civil and Environmental Engineering and MEMS, came to Duke in August 2023 for many of the same reasons. “Duke is a phenomenal place for the things that I do,” he said, which is developing data-driven and computational frameworks to predict, control and engineer the behavior of complex material systems. “It’s such a great place to have this interdisciplinary type of research. Its size and the quality of people really help with that.”

That includes having a strong medical school that promotes research at the intersection of medicine and engineering, he added. “We just bump into each other in the hallway. These aspects are pretty unique at Duke, which is really invested in fundamentally disruptive research.”

Interdisciplinary Approach to Speaking the Same Language

Soft matter researchers have traditionally been isolated within their respective chemistry, physics and engineering departments, often missing opportunities for collaboration. However, this dynamic is changing. As noted by Stefan Zauscher, co-director of the Duke Material Initiative and professor in MEMS, the field of soft matter research is “bringing together disparate communities that study similar phenomena from different perspectives.”

Such collaboration is essential for driving further advancements. By recognizing the significance of soft matter, researchers can uncover new insights and innovative solutions. “Soft matter research encourages fresh thinking about a wide range of materials and can lead to diverse approaches for solving problems,” Zauscher explained.

For instance, while a biomedical approach to a medical issue might seem highly specialized, viewing it through a soft matter lens reveals broader concepts that can be applied across various fields.

“That’s where the real power lies,” Zauscher emphasized. “Soft matter studies can identify commonalities and capture ideas that can then be applied to problems we hadn’t previously considered.”

“Can we design molecular solutions to important diseases? Can we develop materials that can change shape, evolve like our bodies, mutate and adjust to environmental conditions, and then age and degrade to enable their recyclability?” Rubinstein asked. “We know it’s possible because we exist. But designing such ‘living’ materials requires a deeper understanding of fundamental concepts in this new area of science.”