Wednesday, May 22

Associative Polymers Research Challenges 30-Year-Old Dogma 2023

Associative polymers, which have unique self-healing and flow capabilities, may work differently at the molecular level, according to a University of Virginia study.

LIHENG CAI, an assistant professor of materials science and engineering and chemical engineering at UVA, led the study and said the new discovery has important implications for the countless ways these materials are used every day, from engineering recyclable plastics to human tissue engineering to controlling paint consistency so it doesn’t drip.

New associative polymers made by Cai’s UVA School of Engineering and Applied Science postdoctoral researcher Shifeng Nian and Ph.D. student Myoeum Kim allowed the finding, which was reported in Physical Review Letters. A theory Cai co-developed before joining UVA in 2018 led to the result.

“Shifeng and Myoeum essentially created a novel experimental platform to study associative polymer dynamics in ways that weren’t possible before,” Cai added.

“This gave us a new perspective on polymers’ behavior and provides opportunities to improve our understanding of particularly challenging polymer science areas. The research also advances self-healing materials with customizable features.

Monomers form polymers, macromolecules. Scientists can create polymeric materials with specific properties by rearranging or combining these components and manipulating their linkages.

Polymers may shift from hard and inflexible, like glass, to rubbery or even fluid depending on temperature or force, like passing a solid gel through a hypodermic needle.

Reversible bonds hold their moieties customizable molecular subunits together.

This method gives polymers macroscopic characteristics. Associative polymers solve some of the biggest sustainability and health issues. Associative polymers are utilized to make strong self-healing polymers, fuel viscosity modifiers, and biomaterials with important physical qualities for tissue engineering and regeneration.

The UVA team overcame a material characteristic that has plagued researchers for years. Scientists work with materials that break and re-form at “laboratory time scales,” which they can examine through tests. Most experimental systems agglomerate moieties into tiny clusters, making it difficult to analyze the link between reversible bonds and polymer behavior.

Cai’s team used these novel associative polymers to accurately analyze how reversible interactions affect their behavior.

Dynamics and behavior include viscosity (how readily a substance flows) and elasticity (its ability to bounce back after being deformed). To build a biomaterial compatible with human tissue that can reconstitute after injection, a blend of these properties is desirable.

For 30 years, it was believed that reversible bonds crosslink to form rubbery materials. The UVA-led team found otherwise.

The researchers carefully studied their polymers’ flow behavior in a wide range of time scales alongside Shiwang Cheng, an assistant professor in Michigan State University’s chemical engineering and materials science department and flow dynamics expert.

Cheng stated this needs precise control of the polymers’ temperature and humidity. My lab has created techniques and systems for doing so over time.

The connections slowed polymer movement and dissipated energy without generating a rubbery network. Reversible interactions affect polymers’ glassy properties, not viscoelastic range.

“Our associative polymers provide a system for investigating separately the effects of reversible interactions on [polymer] movement and glassy behavior,” Cai added. This may help explain the difficult physics of glassy polymers like plastics.

Cai’s team also created a new molecular theory of associative polymers’ behavior from their research, which might change how to manufacture them with optimum qualities like high stiffness and quick self-healing.

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