{"id":87012,"date":"2023-06-28T13:22:33","date_gmt":"2023-06-28T08:52:33","guid":{"rendered":"https:\/\/polymervapooshesh.ir\/?p=87012"},"modified":"2023-07-02T11:07:40","modified_gmt":"2023-07-02T06:37:40","slug":"counterintuitive-surprise-weaker-bonds-can-make-polymers-10x-stronger","status":"publish","type":"post","link":"https:\/\/polymervapooshesh.ir\/en\/counterintuitive-surprise-weaker-bonds-can-make-polymers-10x-stronger\/","title":{"rendered":"Counterintuitive Surprise! Weaker Bonds Can Make Polymers 10x Stronger"},"content":{"rendered":"

Iranpolymer\/ Baspar\u00a0 <\/em><\/strong>By adding weak linkers to a polymer network, chemists dramatically enhanced the material\u2019s resistance to tearing.<\/p>\n

<\/span>A team of chemists from\u00a0MIT\u00a0and\u00a0Duke University\u00a0has discovered a counterintuitive way to make polymers stronger: introduce a few weaker bonds into the material.
\nWorking with a type of polymer known as polyacrylate elastomers, the researchers found that they could increase the materials\u2019 resistance to tearing up to tenfold, simply by using a weaker type of crosslinker to join some of the polymer building blocks.
\n<\/span>These rubber-like polymers are commonly used in car parts, and they are also often used as the \u201cink\u201d for 3D-printed objects. The researchers are now exploring the possible expansion of this approach to other types of materials, such as rubber tires.
\n\u201cIf you could make a rubber tire 10 times more resistant to tearing, that could have a dramatic impact on the lifetime of the tire and on the amount of microplastic waste that breaks off,\u201d says Jeremiah Johnson, a professor of chemistry at\u00a0MIT<\/span>\u00a0and one of the senior authors of the study, which was published on June 22 in the journal\u00a0Science<\/em>.<\/p>\n

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A significant advantage of this approach is that it doesn\u2019t appear to alter any of the other physical properties of the polymers.
\n\u201cPolymer engineers know how to make materials tougher, but it invariably involves changing some other property of the material that you don\u2019t want to change. Here, the toughness enhancement comes without any other significant change in physical properties \u2014 at least that we can measure \u2014 and it is brought about through the replacement of only a small fraction of the overall material,\u201d says Stephen Craig, a professor of chemistry at Duke University who is also a senior author of the paper.
\nThis project grew out of a longstanding collaboration between Johnson, Craig, and Duke University Professor Michael Rubinstein, who is also a senior author of the paper. The paper\u2019s lead author is Shu Wang, an MIT postdoc who earned his PhD at Duke.
\n<\/span><\/p>\n

The weakest link
\n<\/strong>Polyacrylate elastomers are polymer networks made from strands of acrylate held together by linking molecules. These building blocks can be joined together in different ways to create materials with different properties.
\nOne architecture often used for these polymers is a star polymer network. These polymers are made from two types of building blocks: one, a star with four identical arms, and the other a chain that acts as a linker. These linkers bind to the end of each arm of the stars, creating a network that resembles a volleyball net.
\nIn a 2021 study, Craig, Rubinstein, and MIT Professor Bradley Olsen teamed up to measure the strength of these polymers. As they expected, they found that when weaker end-linkers were used to hold the polymer strands together, the material became weaker. Those weaker linkers, which contain cyclic molecules known as cyclobutane, can be broken with much less force than the linkers that are usually used to join these building blocks.
\nAs a follow-up to that study, the researchers decided to investigate a different type of polymer network in which polymer strands are cross-linked to other strands in random locations, instead of being joined at the ends.
\nThis time, when the researchers used weaker linkers to join the acrylate building blocks together, they found that the material became much more resistant to tearing.
\nThis occurs, the researchers believe, because the weaker bonds are randomly distributed as junctions between otherwise strong strands throughout the material, instead of being part of the ultimate strands themselves. When this material is stretched to the breaking point, any cracks propagating through the material try to avoid the stronger bonds and go through the weaker bonds instead. This means the crack has to break more bonds than it would if all of the bonds were the same strength.
\n\u201cEven though those bonds are weaker, more of them end up needing to be broken, because the crack takes a path through the weakest bonds, which ends up being a longer path,\u201d Johnson says.<\/p>\n

Tough materials<\/h4>\n

Using this approach, the researchers showed that polyacrylates that incorporated some weaker linkers were nine to 10 times harder to tear than polyacrylates made with stronger crosslinking molecules. This effect was achieved even when the weak crosslinkers made up only about 2 percent of the overall composition of the material.
\nThe researchers also showed that this altered composition did not alter any of the other properties of the material, such as resistance to breaking down when heated.
\n\u201cFor two materials to have the same structure and same properties at the network level, but have an almost order of magnitude difference in tearing, is quite rare,\u201d Johnson says.
\nThe researchers are now investigating whether this approach could be used to improve the toughness of other materials, including rubber.
\n\u201cThere\u2019s a lot to explore here about what level of enhancement can be gained in other types of materials and how best to take advantage of it,\u201d Craig says.
\nReference: \u201cFacile mechanochemical cycloreversion of polymer cross-linkers enhances tear resistance\u201d by Shu Wang, Yixin Hu, Tatiana B. Kouznetsova, Liel Sapir, Danyang Chen, Abraham Herzog-Arbeitman, Jeremiah A. Johnson, Michael Rubinstein and Stephen L. Craig, 22 June 2023,\u00a0Science<\/em>.
\nDOI: 10.1126\/science.adg3229
\nThe group\u2019s work on polymer strength is part of a National Science Foundation-funded center called the\u00a0Center for the Chemistry of Molecularly Optimized Networks. The mission of this center, directed by Craig, is to study how the properties of the molecular components of polymer networks affect the physical behavior of the networks.<\/p>\n

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