Study Of Mechanical Behavior And Mechanism Of Amorphous Polymer Based On Molecular Entanglement And Relxation Domain Model

Amorphous polymer has been widely used in engineering and life,and it is inevitable that it will be deformed under the excitation of various environments.Therefore,it is of great significance to study the mechanical response of amorphous polymer under multifield coupling and to reveal its molecular mechanism for the application and design of amorphous polymer.Based on the theory of molecular entanglement and relaxation domain,a mechanical constitutive model based on the molecular mechanism of polymer was proposed in this paper,and the mechanical response of amorphous polymer under the action of heat/solution was analyzed in combination with Flory solution theory.In chapter 2,based on the molecular entanglement theory,it is considered that the mechanical behavior of amorphous polymers is affected by cohesive entanglement and topological entanglement.In combination with the affine network model of polymers,a polymer constitutive model is given which is affected by temperature and strain rate.In the process of deformation,in addition to the change of the elastic potential energy of the polymer chain,the density of the cohesive entanglement also changes,leading to the emergence of yield peak and strain softening.The density and flexibility of topological entanglement determine the stress platform region of the amorphous polymer after strain softening.The change of the density of cohesive entanglement with deformation at different strain rates and temperatures is analyzed,and the mechanical response of amorphous polymers at different opening rates of cohesive entanglement is given.The relationship of yield stress with temperature and strain rate was analyzed.In chapter 3,the variation of yield stress of amorphous polymers with temperature and strain rate is analyzed from the perspective of polymer relaxation through relaxation domain theory.Based on the modified Eyring equation,the relationship between polymer activation energy and relaxation time with temperature and external force was given,and the equivalent relationship between strain rate and temperature on polymer yield stress was analyzed by WLF equation.Based on the change of relaxation domain size with temperature and external force,the concept of "yield domain size" is put forward,which is used as the criterion to judge whether the amorphous polymer is yielding or not.In chapter 4,based on Flory solution theory,the swelling equilibrium of amorphous polymer under the action of solvent is analyzed,and the constitutive relation of glass state of amorphous polymer under the influence of solvent is given.Based on the theory of Flory solution and the theory of molecular entanglement,the influence of solvent on polymer entanglement was discussed.The solvent will cause the polymer entanglement to open and cause physical swelling.At the same time,the solvent will have a chemical plasticizing effect with the entanglement to increase its flexibility.Both of these effects reduce the temperature of the glass transition of the polymer,increase its flexibility,and decrease its stress.