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

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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.