Discovery challenges 30-year-old dogma in associative polymers analysis

A College of Virginia-led examine a few class of supplies referred to as associative polymers seems to problem a long-held understanding of how the supplies, which have distinctive self-healing and circulation properties, operate on the molecular degree.

Liheng Cai, an assistant professor of supplies science and engineering and chemical engineering at UVA, who led the examine, mentioned the brand new discovery has vital implications for the numerous methods these supplies are used on daily basis, from engineering recyclable plastics to human tissue engineering to controlling the consistency of paint so it does not drip.

The invention, which has been revealed within the journal Bodily Evaluate Letters, was enabled by new associative polymers developed in Cai’s lab on the UVA Faculty of Engineering and Utilized Science by his postdoctoral researcher Shifeng Nian and Ph.D. scholar Myoeum Kim. The breakthrough advanced from a concept Cai had co-developed earlier than arriving at UVA in 2018.

“Shifeng and Myoeum primarily created a novel experimental platform to check the dynamics of associative polymers in ways in which weren’t attainable earlier than,” Cai mentioned.

“This gave us a brand new perspective on the polymers’ conduct and offers alternatives to enhance our understanding of significantly difficult areas of examine in polymer science. And from a know-how standpoint, the analysis contributes to the event of self-healing supplies with tailor-made properties.”

Polymers are macromolecules composed of repeating models, or monomers. By rearranging or combining these models and tinkering with their bonds, scientists can design polymeric supplies with particular traits.

Polymers can also change states, from onerous and inflexible, like glass, to rubbery and even fluid relying on components equivalent to temperature or pressure—for instance, pushing a stable gel via a hypodermic needle.

Associative polymers are particularly distinctive: Their moieties—a common time period for molecular subunits with customizable bodily properties—are held collectively by reversible bonds, which means they’ll break aside and re-form.

This course of allows macroscopic properties inaccessible by typical polymers. Consequently, associative polymers present options to a number of the most urgent challenges in sustainability and well being. For instance, associative polymers are used as viscosity modifiers in fuels, to create powerful self-healing polymers, and to engineer biomaterials with bodily properties crucial to tissue engineering and regeneration.

One key to the UVA staff’s work was overcoming a fabric function that has stymied researchers for years. Within the lab, scientists work with supplies whose bonds can break and re-form at “laboratory time scales,” which means inside time frames they’ll observe via experiments. Nevertheless, in practically all present experimental programs, the moieties mixture into small clusters, which prevents exact examine of the connection between reversible bonds and polymer conduct.

Cai’s staff developed new varieties of associative polymers the place the bonds are evenly distributed all through the fabric and at a variety of densities. To substantiate that their supplies don’t type clusters, the researchers collaborated with Mikhail Zhernenkov, a scientist on the U.S. Division of Power’s Brookhaven Nationwide Laboratory. They performed experiments utilizing a classy X-ray instrument—the delicate matter interfaces beamline—on the Nationwide Synchrotron Mild Supply II to disclose the internal make-up of the polymers with out damaging the samples.

These new associative polymers allowed Cai’s staff to exactly examine the consequences of reversible interactions on the dynamics of associative polymers.

Dynamics and conduct seek advice from traits such because the temperature at which molecule motion slows to a inflexible “glassy” state, viscosity (how freely a fabric flows) and elasticity (its capability to snap again after being de-formed). A mixture of these traits is commonly fascinating to design, for instance, a biomaterial appropriate with human tissue that may reconstitute itself after injection.

For 30 years, it had been accepted that when the reversible bonds stay intact, they act as crosslinkers, leading to a rubbery materials. However that is not what the UVA-led staff discovered.

Collaborating with Shiwang Cheng, an assistant professor in Michigan State College’s chemical engineering and supplies science division and an skilled in circulation dynamics, the staff exactly measured the circulation conduct of their polymers in a variety of time scales.

“This requires cautious management over the native atmosphere, equivalent to temperature and humidity of the polymers,” Cheng mentioned. “Over time, my lab has developed a set of strategies and programs for doing so.”

The staff discovered that the bonds can decelerate polymer motion and dissipate power with out making a rubbery community. Unexpectedly, the analysis confirmed that reversible interactions affect the polymers’ glassy qualities moderately than their viscoelastic vary.

“Our associative polymers present a system that enables for investigating individually the consequences of reversible interactions on [polymer] motion and glassy conduct,” Cai mentioned. “This will likely supply alternatives to enhance the understanding of the difficult physics of glassy polymers like plastics.”

From their experiments, Cai’s staff additionally developed a brand new molecular concept that explains the conduct of associative polymers, which might shift fascinated about the best way to engineer them with optimized properties equivalent to excessive stiffness and speedy self-healing capability.

Along with Nian, Kim, Cheng and Zhernenkov, Cai collaborated with Ting Ge, a computational simulations skilled and assistant professor of chemistry and biochemistry on the College of South Carolina, and Quan Chen from the State Key Lab of Polymer Physics and Chemistry on the Changchun Institute of Utilized Chemistry, who supplied the preliminary code for analyzing the circulation conduct of polymers.

The paper, “Dynamics of Associative Polymers with Excessive Density of Reversible Bonds,” seems within the June 2 difficulty of Bodily Evaluate Letters, and is featured as an Editors’ Suggestion.