Molecular Studies of Phase Transitions in Soft Matter - Melting and Crystallization Processes

近年来，随着新的实验发现的出现和/或对现有理论的重新审视，聚合物熔融和结晶的基础经历了深刻的转变，导致对这些现象的潜在机制的重新思考。迫切需要更好地把握这一问题，因为预计不仅在基础科学方面，而且在技术应用方面也会产生影响，加拿大越来越重视这一联系。由于采用了一种新的方法来研究相变，如玻璃、spinodal以及中间相和纳米晶体熔化转变，我们希望带来的新视角解决了这个问题。我们的方法依赖于全原子模拟方法的使用。***报告了实验熔化，Tm和结晶，Tc，温度相对于晶体片层厚度的反比，导致两条直线，但斜率不同。因此，在有限厚度处存在相交，导致Tc高于Tm的意外结果。为了证明这一结果的合理性，有人认为晶体的发育分为两个步骤。晶体首先形成，然后转变为片层晶体。Strobl提出了纠缠链结晶形成中间相的多步骤过程。因此，我们打算利用全原子模拟来解决相变问题，以处理这种特殊的行为。本提案旨在解决的核心问题是：全原子模拟是否可以实现结晶线？为了解决这个问题，我们提出了两个方向：1)改进用于揭示熔化线的建模系统；2)根据轴1中讨论的程序建立从系统熔体中获得晶体的程序。同时，对中间相的研究，根据strobel模型的结晶组成部分，以及与半结晶聚合物研究密切相关的玻璃化转变，仍在继续。因此，在研究模拟结晶线的同时，我们认为熔化、结晶、中间相、玻璃化转变等一系列研究都将受到影响。这个建议最终可以解决的一个典型问题是：在熔融和玻璃化转变温度之间是否存在经验联系，这个比例通常在1.2到1.3之间。总之，这个建议中使用的模拟实验方法越来越被认为是研究科学的第三种方法。因此，它非常具有创新性，并为HQP提供多学科培训，HQP在当今的就业市场上发挥着至关重要的作用。

The foundations of polymer melting and crystallization have experienced a profound shift in recent years, as new experimental findings have emerged and/or revisit of established theories have been proposed, leading to a reconsideration of the underlying mechanisms for these phenomena. It has became urgent to better grasp this problematic since impacts are anticipated not only in fundamental science, but also in technological applications, a link that is more and more fostered in Canada. The novel perspective we wish to bring with this proposal addresses the matter thanks to a new approach to study phase transitions such as glass, spinodal, as well as mesophase and nanocrystal melting transitions. Our methodology relies on the use of an all-atom simulation approach. ***Reporting the experimental melting, Tm, and crystallization, Tc, temperatures with respect to the inverse of the crystal lamellar thickness, leads to two straight lines, but with different slopes. Accordingly there is an intersect at a finite thickness leading to an unexpected result where Tc becomes higher than Tm. To justify this outcome, it has been argued that the crystal development occurs into two steps. Crystallites form first, followed by a change into lamellar crystallites. The multi-step process for the entangled chains to crystallize was proposed by Strobl leading to the formation of a mesophase. We will thus intend to take advantage of the all-atom simulation in solving phase transition problems to handle this particular behavior. The central question this proposal aims to address is thus: Is the crystallization line achievable by all-atom simulation? To address this issue, we propose two axis: 1) Improve the modeled systems used to reveal the melting line; 2) Establish a procedure to get crystals from systems melt according to the procedure discussed in Axis 1. Simultaneaously, studies on mesophases, a component of crystallization according to the Strobl's model, and the glass transition, intimately linked to the study of semi-crystalline polymers, continue. Accordingly, beneath studying the crystallization line from simulation, we claim that a broad range of studies regarding melting, crystallization, mesophases, glass transition will be impacted. As a characteristic question this proposal can ultimately address, is: Is there a justification of the empircal link between the melting and the glass transition temperatures, the ratio usually ranges between 1.2 and 1.3. In conclusion, this experimental approach of simulation exploited in this proposal, is increasingly recognized as a third way of doing science. It is thus very innovative, and provides multidisciplinary training to HQP, a vital role nowadays in the job market.