{"id":28530,"date":"2019-03-11T10:54:45","date_gmt":"2019-03-11T14:54:45","guid":{"rendered":"https:\/\/college.unc.edu\/?p=28530"},"modified":"2024-07-02T17:10:40","modified_gmt":"2024-07-02T17:10:40","slug":"pbdt","status":"publish","type":"post","link":"https:\/\/collegearchive.unc.edu\/?p=28530","title":{"rendered":"Interdisciplinary team discovers double helix structure in synthetic macromolecule"},"content":{"rendered":"
\"Theo
Theo Dingemans (photo courtesy of Innovate Carolina)<\/figcaption><\/figure>\n

Researchers have discovered that a high-strength polymer called \u201cPBDT\u201d has a rare double helix structure, opening possibilities for use in a variety of applications.<\/p>\n

This discovery, recently published in Nature Communications<\/a>, comes as an extension of the development of a polymer ion-gel<\/a>, which promises to outperform conventional flammable liquid battery electrolytes. Now, equipped with evidence of the double helix structure, the potential for this high-performance material extends well beyond batteries.<\/p>\n

\u201cThis polymer has been around for 30 years, and no one had figured out that it\u2019s a double helix,\u201d said Associate Professor of Chemistry Lou Madsen at Virginia Tech, who led this research. \u201cDouble helices in synthetic systems are essentially unheard of.\u201d<\/p>\n

Madsen led an international collaboration, which included Virginia Tech professors Rui Qiao (mechanical engineering) and Robert Moore (chemistry), as well as Theo Dingemans<\/a> at the University of North Carolina at Chapel Hill’s College of Arts & Sciences and Bernd Ensing at the University of Amsterdam in the Netherlands. All three Virginia Tech professors are affiliated with the Macromolecules Innovation Institute<\/a>.<\/p>\n

“The ability to assemble high-strength polymers into double helices is a major expansion of the soft matter molecular tool box,” Dingemans said. “In fact, we\u2019re currently exploring how this design rule can be used to prepare a new generation of nanocomposites that offer both light-weight and unusually high mechanical performance.”<\/p>\n

Rigidity could aid new composites<\/b><\/h3>\n

Composites are engineering materials that bond multiple components to create a new set of improved properties.<\/p>\n

Tires and modern plane fuselages are examples of composites. They require a core material, such as rubber in the tires example, to be mixed with other materials, such as reinforcing fiber fillers, for added strength.<\/p>\n

Madsen and his team had already shown in 2016 that PBDT could mix with liquid ions to create a solid battery electrolyte.<\/p>\n

\u201cBefore we were confident about this double helix, we discovered PBDT could mix with liquid ions and make this electrolyte that has very good conductivity and is also mechanically stiff,\u201d Madsen said. \u201cWe made something with PBDT, but we wanted to know why it works so well. We had evidence it was a double helix but hadn\u2019t appreciated most of its features.\u201d<\/p>\n

Double helix structures, such as DNA, are well known in nature, and they have high bending stiffness. DNA has a diameter of about 2.5 nanometers and is rigid up to about 50 nanometers in length, where it begins to bend. That creates a \u201crigidity ratio\u201d of about 20 to 1, similar to a carrot stick.<\/p>\n

In comparison, PBDT has a rigidity ratio of 1,000 to 1, making it one of the stiffest molecules yet discovered.<\/p>\n

The polymer\u2019s supreme rigidity means that only a fraction of it would be needed to achieve comparable performance to conventional reinforcing fillers. Furthermore, the process for creating it is extremely cheap and easy.<\/p>\n

\u201cIf you\u2019re using conventional fillers in a composite, you might use 10 percent to get the properties you want,\u201d Madsen said. \u201cBut PBDT has this long stiffness length and a tiny diameter. This means you might only have to put in 1 or 2 percent to get a material that\u2019s highly enhanced.\u201d<\/p>\n

\"\"
X-ray pattern of double helix macromolecule \u201cPBDT\u201d with \u201ccross\u201d reminiscent of Rosalind Franklin\u2019s DNA pattern (left). Basic molecular structure (upper right) and computer simulation (lower right) of PBDT.<\/figcaption><\/figure>\n

From X-rays and DNA to computational modeling<\/b><\/h3>\n

Back in 2014, Madsen and his Ph.D. student Ying Wang had thought the polymer was a double helix but didn\u2019t have sturdy evidence. They then began X-ray studies on PBDT, similar to the studies that Rosalind Franklin conducted on DNA in the early 1950s that led to the discovery of the DNA double helix. Sure enough, the PBDT X-ray was similar to Franklin\u2019s DNA X-ray. They further used a technique similar to MRI to bolster their evidence.<\/p>\n

Madsen then turned to Ensing in Holland and then to Qiao at Virginia Tech for help in understanding the polymer with computational models.<\/p>\n

Qiao said he initially didn\u2019t think the simulation would even work.<\/p>\n

\u201cA simulation of a self-assembly to form a double helical structure \u2014 I had never heard of it except people had done it for DNA,\u201d Qiao said. \u201cBut for this kind of simulation, it\u2019s very difficult. My student tried anyway and miraculously it worked. We tried a bunch of different conditions, different ways of running simulations, but the results were robust, which gave us some confidence that it is a real double helix.\u201d<\/p>\n

The confirmation of the double helix structure opens up possibilities for PBDT\u2019s potential application beyond battery electrolytes, such as lightweight aerospace materials.<\/p>\n

\u201cThe application of this is really going to be limited by our imagination,\u201d Qiao said. \u201cNow we have a new kind of Lego piece. As more people hear about this material, they will come up with their own way of using it. What will really come out of it, we may not envision today.\u201d<\/p>\n

Wang, who graduated from Madsen\u2019s group with her doctorate in 2017, is first author of the paper. Other Virginia Tech researchers involved were Carla Slebodnick, research associate professor in the Department of Chemistry specializing in X-ray crystallography; Yadong He and Zhou Yu from Qiao\u2019s lab; Gregory Fahs from Moore\u2019s lab; and Curt Zanelotti from Madsen\u2019s lab.<\/p>\n

This work was funded by a $440,000 National Science Foundation grant in\u00a0“Multi-Scale Self-Assembled Structure and Properties in Polymeric Molecular Composites<\/a>.\u201d<\/p>\n

Story courtesy of Virginia Tech<\/em><\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Researchers have discovered that a high-strength polymer called \u201cPBDT\u201d has a rare double helix structure, opening possibilities for use in a variety of 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