The Constructions and Pyrolysis of 3D Kerogen Macromolecular Models: Experiments and Simulations

Generation and properties of the new asphalt binder model using molecular dynamics (MD)

Asphalt binder is the main material for road pavement and building construction. It is a complex mixture composed of a large number of hydrocarbons with different molecular weights. The study of asphalt binders and asphalt concretes from a molecular perspective is an important means to understand the intricate properties of asphalt. Molecular dynamics simulation is based on Newton's law and predicts the microscopic performance of materials by calculating the intra- and intermolecular interactions. The asphalt binder can be divided into four components: saturates, aromatics, resins, and asphaltenes (SARA). A new molecular model of asphalt was proposed and verified in this study. Eight molecules selected from the literature were used to represent the four components of asphalt. The AMBER Cornell Extension Force Field was applied in this study to model building and the calculation of properties. The density of the asphalt model was calculated and compared with experimental results for validity verifications. The results show that the purposed model can be used to calculate the microscopic properties of the asphalt binder because the density of the model is close to the real value in the field. Besides, the proportions of different molecules in the model were adjusted to predict the relationship between the asphalt binder density and the hydrocarbon ratios and heteroatom contents of the molecular model. Moreover, the glass transition temperature of the asphalt binder model is predicted by the simulation of the heating process. The range of the glass transition temperature is determined by calculating the relationship between specific volume and temperature, and the calculated range is close to the experimental value.

Insights into Adsorption Characterization of Sulfated Xylans onto Poly(ethylene terephthalate)

The main aim of this investigation was to study the interaction of sulfated xylans as antithrombotic substances with poly(ethylene terephthalate) (PET) model films as a model for blood contacting surfaces. The adsorption of sulfated xylans onto PET model films was studied as a function of pH and ionic strength using the quartz crystal microbalance with dissipation (QCM-D) technique. The application of positively charged polyethyleneimine (PEI) as an anchoring polymer was done to improve the adsorption. The hydrophilic/hydrophobic properties of functionalized PET surfaces were monitored by goniometry, whilst their elemental composition was determined by X-ray photoelectron spectroscopy. Sulfated xylans adsorbed favorably at pH 5 by physical interactions and by entropy gain driven adsorption. Higher ionic strengths of solutions improved adsorption, due to the reduction of electrostatic repulsive forces between PET surfaces and anionic xylans’ macromolecules. The intermediate PEI layer caused more extensive and stable adsorption due to Coulomb interactions. The surface modifications presented in this work provided important information regarding the adsorption/desorption phenomena between antithrombotic sulfated xylans and PET surfaces. The latter is of great interest when preparing advanced polymer composite material such as functional antithrombotic PET surfaces for blood-contacting medical devices and presents an extremely challenging research field.

New modeling method to simulate asphaltenes at oil sands process in water management

The study of various structures, physicochemical structures and dynamic characteristics of oil-water interface asphaltenes is an important basis for the large-scale development and efficient clean utilization of oil sands. The molecular dynamics simulations method provides a possibility for revealing the physicochemical structure and dynamic characteristics of oil sands. The emphasis of this paper is to study the physic-chemical structure of tar sands asphaltenes and the changes of their kinetic properties by using molecular dynamics simulations. Molecular dynamics was used to simulate the physicochemical and dynamic characteristics of asphaltenes in water treatment of the oil sands. In this research, the structural and dynamic properties of asphaltenes, such as density distribution, correlation (radial distribution function), root-mean-square deviation (RMSD), and mean azimuth shift (MSD), diffusion coefficient, the radius of gyration, volume viscosity and free energy in water treatment were systematically discussed. The simulation results of asphaltene at the oil-water interface revealed that, in the oil-water interface, oil and water will affect the solubility of asphaltene. The asphaltene molecules have different mobility and the ability to break molecular association, indicating that the structure and dynamic properties of asphaltene in the oil-water interface and the water-water interface are different.