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

A College of Virginia-led research a couple of 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 movement properties, operate on the molecular stage.

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

The invention, which has been printed within the journal Bodily Evaluation Letters, was enabled by new associative polymers developed in Cai’s lab on the UVA College of Engineering and Utilized Science by his postdoctoral researcher Shifeng Nian and Ph.D. scholar Myoeum Kim. The breakthrough advanced from a idea 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 doable earlier than,” Cai stated.

“This gave us a brand new perspective on the polymers’ habits and offers alternatives to enhance our understanding of notably difficult areas of research 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 laborious and inflexible, like glass, to rubbery and even fluid relying on elements comparable to temperature or power—for instance, pushing a stable gel by means of 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 permits macroscopic properties inaccessible by typical polymers. Consequently, associative polymers present options to among the most urgent challenges in sustainability and well being. For instance, associative polymers are used as viscosity modifiers in fuels, to create robust self-healing polymers, and to engineer biomaterials with bodily properties crucial to tissue engineering and regeneration.

One key to the UVA workforce’s work was overcoming a fabric characteristic 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 by means of experiments. Nevertheless, in practically all current experimental programs, the moieties mixture into small clusters, which prevents exact research of the connection between reversible bonds and polymer habits.

Cai’s workforce developed new forms of associative polymers the place the bonds are evenly distributed all through the fabric and at a variety of densities. To verify that their supplies don’t kind clusters, the researchers collaborated with Mikhail Zhernenkov, a scientist on the U.S. Division of Vitality’s Brookhaven Nationwide Laboratory. They performed experiments utilizing a classy X-ray instrument—the gentle 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 workforce to exactly research the consequences of reversible interactions on the dynamics of associative polymers.

Dynamics and habits consult with traits such because the temperature at which molecule motion slows to a inflexible “glassy” state, viscosity (how freely a fabric flows) and elasticity (its skill to snap again after being de-formed). A mixture of these traits is commonly fascinating to design, for instance, a biomaterial suitable 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 workforce discovered.

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

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

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

“Our associative polymers present a system that permits for investigating individually the consequences of reversible interactions on [polymer] motion and glassy habits,” Cai stated. “This may increasingly provide alternatives to enhance the understanding of the difficult physics of glassy polymers like plastics.”

From their experiments, Cai’s workforce additionally developed a brand new molecular idea that explains the habits of associative polymers, which might shift occupied with how you can engineer them with optimized properties comparable to excessive stiffness and speedy self-healing skill.

Along with Nian, Kim, Cheng and Zhernenkov, Cai collaborated with Ting Ge, a computational simulations professional 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 offered the preliminary code for analyzing the movement habits of polymers.

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