A Molecular Engineering Approach to Negative Poisson's RatioPolymers

9420843 Griffin该项目描述了一种分子工程方法，以获得具有显着特性的新材料。 负泊松比材料（也称为拉胀材料）在拉伸时横向膨胀。 这与通常的预期不同，因为几乎所有东西在拉伸时都会变薄-例如橡皮筋。 虽然理论上是可能的，但实际上没有已知的拉胀材料的实例。 然而，最近发现，特殊的几何特征能够赋予这种行为，并且可以构建大尺度宏观结构来实现这一点。 此外，特殊的制造技术有时可以通过在某些聚合物材料中诱导不寻常的形态来产生这种效果。 泊松比是材料的基本弹性常数，并且与控制机械响应的其他弹性常数相互关联。 定制泊松比提供了精确控制机械性能的可能性。 已经认识到，这种行为的最终控制在于分子设计的拉胀材料，其将允许仔细定制这种生物体，并且将给出最大的拉胀响应。 该提案描述了两种聚合物类的设计、合成方法和表征，其中每种聚合物类在分子水平上反映了已知在宏观水平上产生拉胀响应的机械操作的几何特征。 %%% 各种特殊的应用可以遵循：紧固件和铆钉，这将变得更胖（更紧密的配合），在试图删除和垫圈和密封，这将更好地座位（收缩）时，在压缩负荷。 还设想了其中拉胀纤维将减少或消除纤维拔出的复合材料，这是复合材料科学中的关键问题之一。 ***

9420843 Griffin This project describes a molecular engineering approach to a new class of materials with remarkable properties. Negative Poisson's ratio materials (also known as auxetic materials) expand laterally when stretched. This is at variance with usual expectation since virtually everything thins when stretched - a rubber band for example. Although theoretically possible there are virtually no known examples of auxetic materials. It has however been recently discovered that special geometric features are capable of imparting this behavior and large scale macroscopic structures can be built to accomplish this. Also, special fabrication techniques can sometimes produce this effect by inducing unusual morphologies in certain polymeric materials. The Poisson's ratio is a fundamental elastic constant of a material and is interconnected to the other elastic constants which govern mechanical response. Tailoring the Poisson's ratio offers the possibility of precise control of mechanical performance. It has been recognized that ultimate control of such behavior lies in a molecularly designed auxetic material which will permit careful tailoring of this bahavior and which will give the maximum auxetic response. This proposal describes the design, the synthetic approach and the characterization of two polymeric classes each of which reflects at the molecular level the geometric features known to be mechanistically operative in producing an auxetic response at the macroscopic level. %%% A variety of extraordinary applications can follow: fasteners and rivets which will get fatter (tighter fit) upon attempted removal and gaskets and seals which will seat better (contraction) when under compression loading. Composites are also envisioned in which an auxetic fiber will reduce or eliminate fiber pull-out, one of the critical problems in composite science. ***