Toward Soft Diamond: Molecular Modeling for the Engineering of Novel Super-tough Materials

分子构建块故意连接在非常规则的三维网络中的材料是越来越感兴趣的对象。这种兴趣部分源于通过自组装方法合成此类材料的能力。根据所用的积木，可以合成各种不同的材料。在一个极端，单个碳原子作为积木导致了钻石，这是自然界中发现的最坚硬的材料。在另一个极端，作为基石的很长的碳氢链导致非常软的塑料。在这两者之间，中等大小和硬度的积木将带来令人兴奋的新材料，这种材料结合了钻石的一些强度和橡胶的弹性。我们的初步研究表明，由两种不同硬度或化学亲和力的构建块组成的网络将形成橡胶，模拟超韧性自然材料的弹性反应，如鲍鱼壳和蜘蛛丝中的粘合剂。这项研究是对其他小组实验工作的补充。它将填补对帮助识别感兴趣的特定材料构型的计算模型的需求的空白。因此，这项研究将为设计超坚韧的“橡胶钻石”提供指导，这种钻石可能成为一种新材料的范例。从长远来看，这可能会对广泛的材料相关行业产生影响。这项工作还将为代表性不足的群体参与研究和编写教材提供机会。由于由有序和无定形微区组成的弹性体中的形变阻力与重新排列这些微区所需的自由能成本有关，因此可以假设规则网络的弹性性质可以通过构建块来优化，这种构建块允许控制(由变形驱动的)基本有序-无序相变的自由能垒。因此，我们的计划是协同利用能够形成熵驱动的液晶有序(如半柔性链)和焓驱动的微分离有序相(如嵌段共聚物)的链的自组装特性来调节没有缺陷或最小缺陷的端链交联网络的非线性弹性行为。其目的是调节与锯齿形弹性响应相关的自由能势垒的高度和数量。分子动力学模拟将被用来研究不同嵌段共聚物(其嵌段的焓亲和力或主链柔性不同)以及非理想结构和缺陷对弹性行为的影响。

Materials where molecular building blocks are purposely connected in very regular three-dimensional networks are the object of increasing interest. This interest stems in part from the ability to synthesize such materials via self-assembly methods. Depending on the building block used, widely varied materials could be synthesized. At one extreme, a single carbon atom as building block leads to diamond, the hardest materials found in nature. At the other extreme, a very long hydrocarbon chain as building block leads to very soft plastics. In between, building blocks of intermediate size and stiffness would lead to exciting new materials that combine some of the strength of diamond with the elasticity of rubbers. Our preliminary studies have revealed that networks made of two types of building blocks that differ in stiffness or chemical affinity would form rubbers that mimic the elastic response of super-tough natural materials such as the adhesive in abalone shells and spiders' silk. This study is complementary to experimental efforts by other groups. It will fill a gap in the need for computational models that help identify specific material configurations of interest. The research will hence provide guidelines for the design of super-tough "rubbery diamonds" that could become a new materials' paradigm. In the long term, this could impact a broad range of materials related industries. The work will also provide opportunities for the involvement of underrepresented groups in research and the development of educational materials. Since the resistance to deformation in an elastomer composed of ordered and amorphous domains is associated with the free energy cost of rearranging those domains, it is postulated that the elastic properties of regular networks can be optimized by using building blocks that allow control of the free-energy barriers of the underlying order-disorder phase transitions (driven by deformation). Accordingly, the plan is to synergistically leverage the self-assembling properties of chains that are capable of forming entropy-driven liquid crystalline order (like semiflexible chains) and enthalpy-driven micro-segregated ordered phases (like block copolymers) to tune the non-linear elastic behavior of end-chain crosslinked networks with no or minimal defects. The aim is to modulate the height and number of free-energy barriers associated with a sawtooth elastic response. Molecular dynamics simulations will be used to investigate the effects on elastic behavior of different block copolymers (whose blocks differ in either enthalpic affinity or backbone flexibility) and of non-ideal architectures and defects.