Many lessons in life are learned from trees. Stick to the position. Good things take time. Bend, do not break. But metaphors aside, our proud squabbling neighbors offer a wealth of scientific wisdom—and we have a lot to learn.
Simply by their existence, trees are nature’s first materials scientists. Like many plants, they have vascular systems, networks of tube-like channels that transport water and other vital nutrients from the root, to the branch, and to the leaf.
A research team at the Beckman Institute for Advanced Science and Technology has developed a chemical process to create foamed polymers with their own vascular systems, controlling the orientation and alignment of hollow channels to provide structural support and efficient fluid transport through the material.
Their work, “Anisotropic foams by forward polymerization” was published in advanced materials.
The structure is made simple
Polymer foams are effective thermal insulators with applications from packaging to refrigeration to home insulation. Hollow channels often form during the polymerization process, but current methods of fine-tuning their structure — or transforming them into something resembling a working vascular system — rely on sophisticated techniques and tools. This team, led by Diego Alzate-Sanchez, sought to design a simpler method.
“In our research group, we’ve noticed these vein-like structures appearing in polymers,” Alzate-Sanchez said. “But while some scientists have just seen the channels as empty voids that weaken the polymer, we’ve seen it as an opportunity to create something productive.” Postdoctoral researcher at the Beckman Institute.
For this University of Illinois team, the naturally occurring channels were not cause for concern, but rather a source of scientific inspiration—or rather, a vital source of inspiration.
listening to papers
Looking at the oak and maple trees dotted on the Urbana campus, the researchers sought to provide the polymeric foam with a vascular system that mimics the structure found in the trees. The organization of the directed system in a parallel structure allows fluids to be transported in one predetermined direction.
“Think of a tree trunk,” said Jeffrey Moore, director of the Beckman Institute and principal investigator on the study. “The water needs to move in the right direction, from the roots to the leaves. It should go from point A to point B in the most direct way possible; not to point C or somewhere else entirely.”
Since movement in one direction is preferable to movement in another, this structure is known as anisotropic, or unequal. Imagine lanes adjacent to traffic on a northbound highway; Traveling east or west is more difficult than going with the current. Previously, most of the vascular systems embedded in foam materials followed an anisotropic structure, in which the channels moved evenly in all directions. If anisotropy is a highway, then isotropy is an arena of bumper cars that weave through one another in winding, multi-directional paths.
More than just liquids
For the material world, the one-way highway of blood vessels offers unique opportunities to conduct more than just water.
In this study, Alzate-Sanchez and his team demonstrate the use of channels to transport fluids through polymers in a predetermined direction; Looking to the future, the ability to manufacture a directional flow could include various forms of energy.
“Materials with anisotropic properties are important. For example, anisotropic heat insulators can conduct heat in one direction and prevent it in the opposite. The same is true for electricity, light, or even sound. Depending on how the foam is aligned, sound can travel in one direction. one, but it will be blocked in the other direction.”
To determine a way to control the cellular composition of the foams — and in particular, strength variance — the team analyzed each component of the chemical reaction used to make the polymer.
The reaction begins with the incorporation of a monomer called clopentadiene diamine or DCPD; A stimulator and a blowing agent to help give the final product its foam-like texture. This mixture, referred to as the resin, is poured into a test tube. Heating the test tube causes forward polymerization, a reaction that cures—or solidifies—the resin into a foamy cellular solid. The end product is poly-DCPD, and the original DCPD monomer has been polymerized.
Three of the reaction components were examined: the type of blowing agent used; The concentration of the blowing agent and the gel-forming time of the resin. Crystallization occurs due to background polymerization, and refers to the delay time before initiation of forward polymerization, when room temperature resin gradually assumes a soft gel-like consistency in a test tube.
The researchers discovered that a resin’s viscosity — or its flowability, a direct result of its softening during the formation period — is the strongest predictor of anisotropy in the final product. In other words, increasing or decreasing the formation time allows direct control of the cellular structure of the foam.
“This work provides a fast and efficient way to create directed vascular structures from simple components and processes,” Moore said.
The team’s comprehensive experimental design included systematically testing 100 different combinations of blowing agent, concentration, and formation time, and measuring levels of anisotropy, stiffness, and degree of porosity achieved with each variation.
Each foam sample was analyzed using X-ray computed tomography. The new coupling of polymeric foam with micro-computed tomography—a technology typically dedicated to analyzing solids—was a unique collaborative project with co-author Marianna Kirsch, associate professor of mechanical sciences and engineering.
“What Beckmann does well is to encourage a culture in which we realize we have a lot to learn from each other, even if our applications are different,” Kirsch said. “This exchange and desire to learn about something other than your core region meant that the idea that our bone tools could be used to describe the porosity in foam suddenly seemed intuitive and intuitive.”
In addition to Alzate-Sanchez, Moore, and Kersh, this study’s co-authors include graduate research assistant Morgan Cencer and recent Materials Science and Engineering graduate Michael Rogalsky and Nancy Sotos, Maybelle Leland Swanlund Chair of Materials Science and Engineering at UIUC.
Scientists discover a faster way to manufacture vascular materials
Diego M. Alzate‐Sanchez et al, Anisotropic foams by forward polymerization, advanced materials (2021). DOI: 10.1002 / adma.202105821
Presented by the University of Illinois at Urbana-Champaign
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