Materials World Network: Healing Polymers: The Self Assembly Approach

由美国凯斯西储大学、密歇根州立大学和英国雷丁大学组成的一个材料世界网络项目，旨在研究超分子聚合物作为一种新型可治愈材料的潜力。本文提出，在超分子聚合物结构中起关键作用的非共价键的动态性质为创造具有快速和容易的热诱导愈合能力的薄膜和涂层提供了可能性。为了实现这一目标，该网络汇集了来自聚合物化学、超分子化学、流变学、纳米复合材料、工程和显微镜等领域的研究人员。传统的热塑性塑料可以通过一种叫做热板焊接的方法进行修复。有人提出，这一过程涉及许多步骤（表面重排，表面接近，润湿，扩散和随机化）。在润湿阶段之后，与界面相关的能垒基本消失，聚合物链可以自由扩散和随机化。为了恢复材料的原始机械强度，这最后两个阶段被认为是重要的。这种修复聚合物裂缝的方法的局限性在于裂缝愈合所需的温度和时间。此外，聚合物的大分子量M会阻碍材料性能的完全恢复。例如，已愈合的断裂应力已被证明与t/M成正比。有人提出，使用超分子聚合物将避免一些这些问题，因为热退火将导致分子量的减少，从而提高愈合的断裂应力和裂纹愈合所需的时间。该网络将研究各种不同的超分子基序，这些基序不仅会自组装成不同的结构，而且会表现出不同的动力学和热力学结合特征，以更好地理解自组装如何影响机械性能。此外，一旦对这种系统有了更好的了解，不仅可以作为可治疗材料，还可以作为粘合剂等领域的应用，可以设想低成本的加工和回收。

A Materials World Network program, which consists of institutions from the US (Case Western Reserve University and Michigan State University) and the UK (University of Reading), has been created to investigate the potential of supramolecular polymers as a new class of healable materials. It is proposed that the dynamic nature of the non-covalent bonds that play a critical role in the structure of a supramolecular polymer offers the possibility of creating films and coatings that exhibit quick and easy thermally-induced healing capability. To achieve this goal this Network has brought together researchers from the fields of polymer chemistry, supramolecular chemistry, rheology, nanocomposites, engineering and microscopy. Traditional thermoplastics can be healed using a process called hot plate welding. It has been proposed that this process involves a number of steps (surface rearrangement, surface approach, wetting, diffusion and randomization). After the wetting stage the energy barriers associated with the interface essentially disappear and the polymer chains are free to diffuse and randomize. It is these last two stages which are believed to be important in order to restore the material's original mechanical strength. The limitations of this approach to heal polymer cracks are the temperatures and time, t, required for the crack to heal. In addition the large molecular weight, M, of the polymer can hinder full recovery of the material properties. For example, the healed fracture stress has been shown to be proportional to t/M. It is proposed that the use of supramolecular polymers will circumvents some of these problems as thermal annealing will result in a decrease in the molecular weight thus improving the healed fracture stress and the time required for the crack to heal. This Network will investigate a variety of different supramolecular motifs which will not only self-assemble into different architectures but will also exhibit different kinetic and thermodynamic binding characteristics to gain a better understanding of how self-assembly affects mechanical properties. Furthermore, once a better understanding of such systems is developed applications not only as healable materials but also in areas such as adhesives, low cost processing and recycling can be envisaged.