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TECH: Goodbye tire changing
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Goodbye tire changing
Imagination or reality
By Fanny Bates

BT 201803 Tech 01      相信大家都看过电影《金刚狼》,影片中男主角铮亮的钢爪和强大的自我修复能力一定让大家印象深刻。其实我们也有自我修复的能力——不管你信不信,最著名的自我修复材料其实是我们的皮肤。如果皮肤被划伤,很快它就可以不治而愈。然而,如果轮胎瘪了,可就不会那么幸运了。不过哈佛大学约翰•保尔森工程与应用科学学院(SEAS)的研究人员最近开发了一种与天然橡胶相当的可自我修复的新型橡胶,或许可以在未来应用于汽车轮胎,这样即使在荒郊野岭我们也不用担心了,轮胎可以在行进中自我修复,减少车祸的发生。

      哈佛大学博士后研究员蔡立恒与中国四川大学客座教授吴金荣及两位同事一起,决定研发一种具有共价键和可逆键的混合橡胶。由于这两种键像油和水一样难以混溶,研究人员开发了一种分子绳来将它们结合在一起,允许它们在分子尺度上均匀混合,从而制造出一种透明、坚韧、可以自愈的橡胶。当力作用在普通橡胶上时,在某些应力点会发生开裂。混合橡胶拉伸时,则会在整个材料中产生一种裂纹,这种裂纹与裂缝相似,但通过纤维束连接在一起。裂纹会重新分配应力,不会导致灾难性的破坏,而一旦应力释放,材料就会恢复到原来的形状,并且自己愈合起来。

      研究人员尚未完全理解这种橡胶为什么在拉伸时会出现裂纹,希望通过更多的研究对自愈橡胶的性能进行探索,开发出可实际应用的自愈合聚合物。

BT 201803 Tech 03Imagine a situation that is well known to all drivers. You are driving to work in the rush hour, you are already late and suddenly your tire goes flat. The situation causes you anguish and discomfort, especially when you don't have enough time to solve the problem. It seems that a research team from Harvard University, John A. Paulson School of Engineering and Applied Sciences (SEAS), has developed a new solution to the problem that has been here since the first modern car appeared in 1886, a new hybrid tire.
 

How Do Self-Healing Materials Work?


The best-known self-healing material is, believe it or not, our skin. If you cut yourself, your skin will heal with no trace within a week. However, if a tire goes flat or you crush your car, you won't be that lucky. In the early 2000s, scientists began conducting studies on materials that could behave like our skin and repair the internal damage by themselves.
 

So how does it function? Basically, a self-healing material has tiny microcapsules filled with glue-like chemicals. So when the damage happens, the microcapsules open and the chemicals inside start pouring out and the crack seals up. The first artificial self-healing materials were polymers, plastics made from long, repeating molecules, so if a crack emerged, it was automatically repaired. In addition to this type of self-healing material, there are also materials with a kind of internal "vascular" circulation similar to blood - shape-memory materials and reversible polymers.

BT 201803 Tech 02 编辑A New Type of Self-Healing Hybrid Tire


When we talk about car tires, minimum tire standards require rubber to pass tests which are conducted when the tire is new. A premium tire will continue to achieve these standards long into its life, while cheaper rubber will reduce these standards and eventually will become worn out. These kinds of problems could be a matter of past.


Self-healing technology is not something that is new in our modern world, but it tends to be very difficult to apply to materials like rubber because it is a solid material. Take, for example, a typical simple rubber. When force is applied to it, a crack usually appears at certain stress point. Rubber is made of polymers which are connected with permanent bonds. These bonds are very strong; however, a true challenge is to try to reconnect them.

Self healing tire 3554 default largeAs reported by Harvard SEAS, Li-Heng Cai, a postdoctoral fellow at SEAS and corresponding author of the paper, explained this by saying that: "Previous research used reversible hydrogen bonds to connect polymers to form a rubber but reversible bonds are intrinsically weaker than covalent bonds. This raised the question, can we make something which is tough but can still self-heal?”


In order to make rubber self-healing, researchers tried to change the very nature of this material, making the bonds stronger and more efficient. They made a "molecular rope" which actually combines two types of bonds, covalent and reversible. By creating this rope, they mixed the unmixable bonds in a homogenous way. When stretched, this new type of rubber would develop creases and fine cracks, which would redistribute stress and allow the material to go back to its original form, thus combining both types of bonds.


Cai, along with Jinrong Wu, a visiting professor from Sichuan University, China, and senior author David A. Weitz, Mallinckrodt Professor of Physics and Applied Physics, developed a hybrid rubber with both covalent and reversible bonds. However, his theory wasn't successful because he wasn't lucky enough to provide valid experiments, Harvard reports say.


Benefits of this discovery would be numerous, especially when it comes to industries that rely on dry, tough materials like rubber. Research has also been done on the field of robotics, computer technology, stretchable electronics, damping materials and many other optical devices. However, a world free of flat tires and car accidents caused by tire changes would be a dream come true for many people. Instead of having a spare tire and conducting tire replacement, the only thing you should do is drive long enough on the road so your tire "cures" itself. However, scientists agree on one fact - a lot of work still needs to be done so that this material would be ready for commercial use.

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