2008年11月27日
到处都是塑料在我们的现代世界中,很大程度上是由于属性呈现材料坚韧耐用,但重量轻,容易可行。欧洲杯足球竞彩他们最有用的特性之一,然而,弯曲的能力而不是打破当把压力之下——也是最令人费解。
这个属性,描述为“塑性流动”,允许许多塑料改变形状吸收能量而不是分裂,说威斯康辛大学马克Ediger麦迪逊化学教授。例如,一个类型的防弹玻璃停止流动围绕它而不破坏的一颗子弹。普通窗玻璃,以这种方式无法流动,只会粉碎。
“这是一个奇怪的组合的属性…这些材料不能欧洲杯足球竞彩够因为他们刚性固体流动,但他们中的一些人可以,”他说。“这是怎么发生的?”Ediger's research team, led by graduate student Hau-Nan Lee, has now described a fundamental mechanism underlying this stiff-but-malleable quality. In a study appearing Nov. 28 in Science Express, they report that subjecting a common plastic to physical stress - which causes the plastic to flow - also dramatically increases the motion of the material's constituent molecules, with molecular rearrangements occurring up to 1,000 times faster than without the stress.
这些快速重组有可能允许的关键材料,以适应不同的条件没有立即开裂。塑料是一种材料化学家和工程师称为聚合物眼镜。与晶体,分子锁在一起,完美有序的数组,一个玻璃分子杂乱,其组成化学构建块被困在任何匆忙地安排他们落入材料冷却和凝固。虽然这比晶体原子障碍意味着眼镜不太稳定,它还提供了分子玻璃有一些回旋余地移动没有分裂。“聚合物眼镜被用在许多不同的应用程序,“包括聚碳酸酯,发现在流行的可重复使用的水瓶,Ediger说。
飞机的窗户也常常用聚碳酸酯制成的。“聚合物使用眼镜的原因之一是,他们不休息当你把它们或飞进一只鸟以每小时600英里的速度。”However, their properties can change dramatically under different physical conditions such as pressure, temperature, and humidity. For example, many polymer glasses become brittle at low temperatures, as anyone knows who has ever dropped a plastic container from the freezer or tried to work on vinyl house siding in cold weather. As plastics become more and more prevalent in everything from electronics to airplanes, scientists and engineers face questions about the fundamental properties and long-term stability of these materials over a range of conditions.
例如,下一代商用飞机正向包括少金属支持更高比例的轻量级的高分子材料——大约50%相比,新的波音787波音777 -只有10%,工程师需要知道这些材料将如何应对不同的压力:硬着陆,强风或温度或湿度的变化。欧洲杯足球竞彩”会如何回应20年后当它变得扭曲,或拉伸,或者压缩?会回应通过吸收能量并保持完整,还是要回应打破债券和飞行的分裂成碎片?”Ediger问道。威斯康辛州的团队研究了常见塑料的力学称为有机玻璃-也被称为有机玻璃或丙烯酸,发现拉力有明显影响的分子内的材料,加快个人运动超过1000倍。
研究小组观察到内部分子重组50秒,已经一整天没有施加的力的大小。他们认为不打破这个运动允许材料流量增加。“当你拉,你增加材料的流动,“Ediger说。”拉着实际上的行为将玻璃转换成液体,然后流。当你停止拉着它,它转换回一个玻璃。”The work has benefited from collaboration between chemists and engineers in a Nanoscale Interdisciplinary Research Team (NIRT) supported by the National Science Foundation (NSF), which includes UW-Madison chemical and biological engineering professor Juan de Pablo and groups at the University of Illinois and Purdue University. "From the most fundamental perspective, we're trying to understand why pulling on a glass allows it to flow," Ediger says. "The answer to that question will help us to better model the behavior of real materials in real applications."