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Equilibration Pathways beyond the a-Relaxation: The Slow Arrhenius Process

par Song, Zijian
Président du jury Losada Perez, Patricia
Promoteur Napolitano, Simone
Publication Non publié, 2022-07-07

Thèse de doctorat

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Résumé :

Polymers are one of the most important, versatile classes of materials. Due to the low cost, easy processing and tuneable properties, polymers are used in a wide range of applications, e.g., items in daily life, composite materials, medical materials, mechanical devices, electronics and photovoltaics1,2. To meet growing challenges in market, fast and efficient processing is required to produce advanced polymeric materials. Under such conditions, chain conformations of polymers are far beyond the thermodynamic equilibrium state (gaussian chain statistics with the minimum of the free energy) due to the processing rate being faster than the inverse of the equilibration time (reptation time). Among a large amount of the geometrical configurations, polymer films have been the most investigated systems by far. In our work, polymer films are fabricated by spincoating of polymer solutions. This work aims to investigate the nonequilibrium effect on polymer films. The presentation of our work is divided into 6 chapters. Firstly, the dielectric relaxation and molecular mobility is introduced in chapter 1. We give a detailed explanation on the physical mechanism and experimental part of irreversibly adsorbed polymer chains onto a solid substrate in chapter 2. In chapter 3, an experimental and modeling comparison of the dynamic of Aluminum-capped and freestanding poly (2-chlorostyrene) (P2ClS) films is shown. We demonstrate that the molecules in proximity to both capping and polymer/air interface contribute to speed up segmental dynamics. In chapter 4, we present a new slow Arrhenius-like molecular process, which is responsible for the macroscopic equilibration of the nonequilibrium polymer melts. Considering the nonequilibrium effects in the formation of polymer/substrate interfaces, our experimental evidence in chapter 5 indicates that the adsorption kinetics of polymer melts onto a solid substrate get slower upon an increase of the monomer/wall interaction. In a good agreement with the model description, we proposed a linear relationship between the adsorption rate and a logarithmic term of the desorption energy.