Science & Technology

Hard and durable elastic polymer solves many years of trouble

Highly entangled hydrogel (left) and regular hydrogel (right). Credits: Suo Lab / Harvard SEAS

Polymer science has enabled rubber tires, Teflon and Kevlar, PET bottles, and nylon jackets, among many other ubiquitous features of everyday life. Elastic polymers, known as elastomers, can be stretched and released repeatedly and are used in applications such as gloves and heart valves that need to last for a long time without tearing. But the conundrum has long confused polymer scientists. Elastic polymers can be hard or tough, but they cannot be both.

This stiffness-toughness conflict poses a challenge for scientists developing polymers that can be used in applications such as tissue regeneration, bioadhesives, bioprinting, wearable electronics, and soft robots.

In the paper published today ChemistryResearchers at Harvard John A. Paulson’s School of Applied Sciences (SEAS) have resolved long-standing conflicts and developed hard, durable elastomers.

“In addition to developing polymers for new applications, scientists face urgent challenges: plastic pollution,” said lead authors of the study, Allen E. and Marilyn M. Packet, Professor of Mechanics and Materials. One Zhigang Suo said. “With the development of biodegradable polymers, we have once again returned to the fundamental question. Why are some polymers tough, others fragile? The polymers tear when stretched repeatedly. How can I prevent it? ”

Polymer chains are made by bonding the components of a monomer together. To make the material elastic Polymer chain Is bridged by Covalent bond..The more crosslinks, the shorter polymer Chain and harder material.

“The shorter the polymer chains, the less energy can be stored in the material, making it more brittle,” said Jantho Kim. graduate student Co-lead author of the treatise at SEAS. “If there are few cross links, the chain will be long and the material will be strong, but it will be too squeezed to be useful.”

To develop a hard and durable polymer, researchers turned to physical rather than physical Chemical bond Link polymer chains. These physical bonds, called entanglements, are known in the field as long as polymer science exists, but have been thought to affect stiffness only, not toughness.

However, SEAS’s research team found that with sufficient entanglement, polymers could become tough without compromising stiffness. To create highly entangled polymers, researchers used concentrated monomer precursor solutions containing one-tenth the water of other polymer recipes.

Hard and durable elastic polymer solves many years of trouble

Each polymer chain has numerous entanglements along its length (left) and crosslinks at both ends. Stretched polymer (center) showing the transfer of tension to other chains. Credits: Suo Lab / Harvard SEAS

Guogao Zhang, a postdoctoral fellow at SEAS and co-lead author of the treatise, said: “Like knit fabrics, polymers maintain their connections by being physically intertwined.”

With hundreds of these entanglements, only a handful of chemical crosslinks are needed to keep the polymer stable.

“As elastomers, these polymers have high toughness, strength, and fatigue resistance,” said Meixuanzi Shi, a visiting researcher and co-author of the paper at SEAS. “When a polymer is submerged in water to form a hydrogel, it has low friction and high wear resistance.”

Its high fatigue resistance and high wear resistance improve the durability and life of the polymer.

“Our research shows that using entanglements rather than crosslinks can increase the durability of the material and reduce the consumption of some plastics,” Zhang said.

“We hope that this new understanding of polymer structures will open up new application opportunities and pave the way for more sustainable and long-lasting polymer materials with these extraordinary mechanical properties,” Kim said. Stated.

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For more information:
Zhigang Suo, polymer breakage, fatigue, friction, where entanglement far exceeds cross-linking, Chemistry (2021). DOI: 10.1126 / science.abg6320

Quote: Hard and durable elastic polymer, a long-standing conundrum obtained on October 7, 2021 from https: // October 7th) will be resolved Standing.html

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Hard and durable elastic polymer solves many years of trouble Hard and durable elastic polymer solves many years of trouble

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