Effect of water in amorphous polyvinyl formal: insights from molecular dynamics simulation

Molecular Dynamic Simulations for Biopolymers with Biomedical Applications

Computational modeling (CM) is a versatile scientific methodology used to examine the properties and behavior of complex systems, such as polymeric materials for biomedical bioengineering. CM has emerged as a primary tool for predicting, setting up, and interpreting experimental results. Integrating in silico and in vitro experiments accelerates scientific advancements, yielding quicker results at a reduced cost. While CM is a mature discipline, its use in biomedical engineering for biopolymer materials has only recently gained prominence. In biopolymer biomedical engineering, CM focuses on three key research areas: (A) Computer-aided design (CAD/CAM) utilizes specialized software to design and model biopolymers for various biomedical applications. This technology allows researchers to create precise three-dimensional models of biopolymers, taking into account their chemical, structural, and functional properties. These models can be used to enhance the structure of biopolymers and improve their effectiveness in specific medical applications. (B) Finite element analysis, a computational technique used to analyze and solve problems in engineering and physics. This approach divides the physical domain into small finite elements with simple geometric shapes. This computational technique enables the study and understanding of the mechanical and structural behavior of biopolymers in biomedical environments. (C) Molecular dynamics (MD) simulations involve using advanced computational techniques to study the behavior of biopolymers at the molecular and atomic levels. These simulations are fundamental for better understanding biological processes at the molecular level. Studying the wide-ranging uses of MD simulations in biopolymers involves examining the structural, functional, and evolutionary aspects of biomolecular systems over time. MD simulations solve Newton's equations of motion for all-atom systems, producing spatial trajectories for each atom. This provides valuable insights into properties such as water absorption on biopolymer surfaces and interactions with solid surfaces, which are crucial for assessing biomaterials. This review provides a comprehensive overview of the various applications of MD simulations in biopolymers. Additionally, it highlights the flexibility, robustness, and synergistic relationship between in silico and experimental techniques.

Characteristics of water absorption in amine-cured epoxy networks: a molecular simulation and experimental study

Moisture corrosion of cured epoxy resins seriously affects the durability of epoxy products and has been a serious issue in scientific and engineering fields. In this study, a series of cured epoxy resins with different structures were prepared by tuning their curing conversion in both experimental and simulation methods. In experiments, the equilibrium water content and the diffusion coefficient of amine-cured epoxy resins were measured by gravimetric measurement. The interaction between water molecules and epoxy network was investigated by time-resolved FTIR, difference spectroscopy and 2D correlation spectroscopy. In simulation, the hydrogen bonds, the mobility of hydroxypropyl ether groups and water molecules, and the free volume with its distributions were analyzed. Five types of water molecules were intuitively observed in this study; free volume had a stronger influence on equilibrium water content than polarity in the bifunctional epoxy/amine system, and the increase in the diffusion coefficient was considered as the result of reduction in motion resistance and an increase in channels for the motion of water molecules.

Molecular Mechanics of the Moisture Effect on Epoxy/Carbon Nanotube Nanocomposites

The strong structural integrity of polymer nanocomposite is influenced in the moist environment; but the fundamental mechanism is unclear, including the basis for the interactions between the absorbed water molecules and the structure, which prevents us from predicting the durability of its applications across multiple scales. In this research, a molecular dynamics model of the epoxy/single-walled carbon nanotube (SWCNT) nanocomposite is constructed to explore the mechanism of the moisture effect, and an analysis of the molecular interactions is provided by focusing on the hydrogen bond (H-bond) network inside the nanocomposite structure. The simulations show that at low moisture concentration, the water molecules affect the molecular interactions by favorably forming the water-nanocomposite H-bonds and the small cluster, while at high concentration the water molecules predominantly form the water-water H-bonds and the large cluster. The water molecules in the epoxy matrix and the epoxy-SWCNT interface disrupt the molecular interactions and deteriorate the mechanical properties. Through identifying the link between the water molecules and the nanocomposite structure and properties, it is shown that the free volume in the nanocomposite is crucial for its structural integrity, which facilitates the moisture accumulation and the distinct material deteriorations. This study provides insights into the moisture-affected structure and properties of the nanocomposite from the nanoscale perspective, which contributes to the understanding of the nanocomposite long-term performance under the moisture effect.

Molecular dynamics simulation of effect of glycerol monostearate on amorphous polyethylene in the presence of water

Polyethylene (PE) is used widely as an electrical insulating material. However, the deterioration of its insulating ability is accelerated by exposure to a humid environment. To prevent the influence of water molecules, mixing 2,3-dihydroxypropyl octadecanoate-known as glycerol monostearate (GMS)-into PE has been proposed. However, the physical mechanism underlying the effect of GMS remains unclear. In the present study, the behavior of water molecules in amorphous PE with and without GMS molecule(s) was investigated in terms of diffusion and clustering using molecular dynamics (MD) simulations. Analyzing the mean square displacement (MSD), diffusion coefficient and radial distribution function (RDF) of the water molecules revealed that GMS contributed to suppressing the diffusion and dispersion of water molecules. Furthermore, it was demonstrated that, in the case of 4 wt% GMS and less than 2 wt% water, GMS contributes to reducing the diffusion coefficient of water molecules but does not change the glass transition temperature (T _g) of the system drastically.