Polymer networks are an important class of materials that are ubiquitously found in natural, biological, and man-made systems. The complex mesoscale structure of these soft materials has made it difficult for researchers to fully explore their properties. In this dissertation, we introduce a coarse-grained computational model for permanently cross-linked polymer networks than can properly capture common properties of these materials. We use this model to study several practical problems involving dry and solvated networks. Specifically, we analyze the permeability and diffusivity of polymer networks under mechanical deformations, we examine the release of encapsulated solutes from microgel capsules during volume transitions, and we explore the complex tribological behavior of elastomers. Our simulations reveal that the network transport properties are defined by the network porosity and by the degree of network anisotropy due to mechanical deformations. In particular, the permeability of mechanically deformed networks can be predicted based on the alignment of network filaments that is characterized by a second order orientation tensor. Moreover, our numerical calculations demonstrate that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. We show that swollen gel capsules allow steady, diffusive release of nanoparticles and polymer chains, whereas gel deswelling causes burst-like discharge of solutes driven by an outward flow of the solvent initially enclosed within a shrinking capsule. We further demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods in the capsule interior. We also probe the effects of velocity, temperature, and normal load on the sliding of elastomers on smooth and corrugated substrates. Our friction simulations predict a bell-shaped curve for the dependence of the friction coefficient on the sliding velocity. Our simulations also illustrate that at low sliding velocities, the friction decreases with an increase in the temperature. Overall, our findings improve the current understanding of the behavior of polymer networks in equilibrium and non-equilibrium conditions, which has important implications for synthesizing new drug delivery agents, designing tissue engineering systems, and developing novel methods for controlling the friction of elastomers.

Very few polymer mechanics problems are solved with only pen and paper today, and virtually all academic research and industrial work relies heavily on finite element simulations and specialized computer software. Introducing and demonstrating the utility of computational tools and simulations, Mechanics of Solid Polymers provides a modern view of how solid polymers behave, how they can be experimentally characterized, and how to predict their behavior in different load environments. Reflecting the significant progress made in the understanding of polymer behaviour over the last two decades, this book will discuss recent developments and compare them to classical theories. The book shows how best to make use of commercially available finite element software to solve polymer mechanics problems, introducing readers to the current state of the art in predicting failure using a combination of experiment and computational techniques. Case studies and example Matlab code are also included. As industry and academia are increasingly reliant on advanced computational mechanics software to implement sophisticated constitutive models – and authoritative information is hard to find in one place - this book provides engineers with what they need to know to make best use of the technology available. - Helps professionals deploy the latest experimental polymer testing methods to assess suitability for applications - Discusses material models for different polymer types - Shows how to best make use of available finite element software to model polymer behaviour, and includes case studies and example code to help engineers and researchers apply it to their work

Computer Simulation of Porous Materials covers the key approaches in the modelling of porous materials, with a focus on how these can be used for structure prediction and to either rationalise or predict a range of properties including sorption, diffusion, mechanical, spectroscopic and catalytic. The book covers the full breadth of (micro)porous materials, from inorganic (zeolites), to organic including porous polymers and porous molecular materials, and hybrid materials (metal-organic frameworks). Through chapters focusing on techniques for specific types of applications and properties, the book outlines the challenges and opportunities in applying approaches and methods to different classes of systems, including a discussion of high-throughput screening. There is a strong forward-looking focus, to identify where increased computer power or artificial intelligence techniques such as machine learning have the potential to open up new avenues of research. Edited by a world leader in the field, this title provides a valuable resource for not only computational researchers, but also gives an overview for experimental researchers. It is presented at a level accessible to advanced undergraduates, postgraduates and researchers wishing to learn more about the topic.

This dissertation, "Modeling and simulation of the mechanical response of biopolymer networks / y Wei Xi" by Xi, Wei, 魏茜, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: The mechanical response of live cells is largely determined by the cytoskeleton, a network composed of different types of biopolymers. In addition to maintain structural integrity and stability of cells, cytoskeleton also plays important roles in the processes like intracellular transport, cell division and locomotion. Although extensive effort has been spent in the past few decades trying to study the nonlinear and viscoelastic properties of bio-filament networks both experimentally and theoretically, fundamental questions such as how thermal fluctuations of biopolymers and the deformability as well as the association/dissociation kinetics of crosslinking molecules, "gluing" individual filaments together, dictate the bulk response of a network remain unsettled. To address these important issues, a computational framework for analyzing the mechanical behavior of biopolymer networks was developed in this thesis on the basis of continuum mechanics. Specifically, a combined finite element-Langevin dynamics(FEM-LD)method was first established to capture the influence of thermal undulations of biopolymers. The validity of this new approach was verified by comparing its results with a variety of theoretical predications. In addition, strategies for the implementation of this method in simulating the dynamic response of realistic filamentous networks have also been developed. Interestingly, it was found that entropic effect will be important when the macroscopic strain level is below 1%, beyond which the network response will be dominated by filament elasticity. After that, formulations taking into account the deformability and failure of crosslinking molecules, along with large deflections of individual filaments, were added to the model. It was shown that the stress-strain relationship of random biopolymer networks typically undergoes linear increase -strain hardening -stress serration -total fracture transitions due to the interplay between the bending and stretching of individual filaments and the deformation and breakage of cross-linkers. Furthermore, the network fracture energy was found to reach its minimum when the crosslinking molecules possess intermediate rotational stiffness, reflecting the fact that most of the strain energy will be stored in the distorted filaments with rigid cross-linkers while the imposed deformation will be "evenly" distributed among significantly more crosslinking molecules with high rotational compliance. Finally, the influence of binding/unbinding kinetics of cross-linkers on the rheological response biopolymer networks was examined and three distinct regimes were identified. At high driving frequencies, the bulk network response will be governed by the mechanics of individual filaments, leading to a 3/4 exponent scaling behavior, while stress relaxation induced by the unbinding of crosslinking molecules will dominate the process at intermediate frequencies. In comparison, the collective effect of multiple dissociation of cross-linkers will result in a power-law rheology behavior (with an exponent of 0.5) when the driving frequency is very low, in broad agreement with experimental observations. Subjects: Biopolymers - Mechanical properties

This book addresses traditional polymer processing as well as the emerging technologies associated with the plastics industry in the 21st Century, and combines engineering modeling aspects with computer simulation of realistic polymer processes. This book is designed to provide a polymer processing background to engineering students and practicing engineers. This three-part textbook is written for a two-semester polymer processing series in mechanical and chemical engineering. The first and second part of the book are designed for a senior- to graduate level course, introducing polymer processing, and the third part is for a graduate course on simulation in polymer processing. Throughout the book, many applications are presented in form of examples and illustrations. These will also serve the practicing engineer as a guide when determining important parameters and factors during the design process or when optimizing a process. Examples are presented throughout the book, and problems and solutions are available.