Molecular Simulations Of Skin-core Structure Formation Of Fibers

We used dynamic Monte Carlo simulations in a 3-dimensional lattice to study skin-core structure in the fibers. In the first chapter we introduced the basic knowledge of synthetic fibers, manufacture methods and existing principle of coagulation of fibers. Then we talk about the discovery of skin-core structure in fibers and studies of wet-spinning by researchers. We learned a lot from the research by the predecessors, but also find some limitation. Scientists used to consider phase separation the only cause of the morphology of fibers and ignore the influence of polymer crystallization. We take advantage of computer simulation which is good at the molecular details in the fast coagulation process to study the cause of skin-core structure in wet-spun fibers in this thesis. we consider both phase separation and polymer crystallization in the coagulation simulation. and we take temperature gradient in the radial direction of fiber at the early stage of coagulation into account. In the end, we introduce the basic knowledge of polymer crystallization, including morphology, models, thermodynamic and kinetics.In Chapter Two we introduced the Monte Carlo simulation principle, such as im-portance sampling, boundary condition and chain motion. There are 16 coordination sets around one set. This makes sampling efficient. System micro-relaxes through one set jump and sets sliding. This makes relax fast and fulfill detailed balance condition. We introduced three energy parameter Ep, B and Ec to drive crystallization and phase separation. So Dynamic Monte Carlo simulation can study the polymer chain motions, polymer crystallization and phase separation at molecule level.In Chapter Three we talked about our simulation method and results.The cause of the skin-core structure is that:temperature gradient caused by the delay thermal conduction together with phase separation caused by the diffusion of non-solvent im-mersing into the polymer solvent. The skin thickness increase with the polymer con-centration. And as the coagulation bath temperature increase, the skin thickness de-crease. However,the skin thickness is not sensitive to the poor solvent property. The poor solvent property can influence the uniform of the fiber cross section morphology.The novelty of our research can be summarized as below:● we use simulation method and get skin-core structure in fiber● we take polymer crystallization into account● we found the cause of skin-core in fiber and give insights to tune fiber structure.