Ali Gooneie

A Review of Multiscale Computational Methods in Polymeric Materials

Polymeric materials display distinguished characteristics which stem from the interplay of phenomena at various length and time scales. Further development of polymer systems critically relies on a comprehensive understanding of the fundamentals of their hierarchical structure and behaviors. As such, the inherent multiscale nature of polymer systems is only reflected by a multiscale analysis which accounts for all important mechanisms. Since multiscale modelling is a rapidly growing multidisciplinary field, the emerging possibilities and challenges can be of a truly diverse nature. The present review attempts to provide a rather comprehensive overview of the recent developments in the field of multiscale modelling and simulation of polymeric materials. In order to understand the characteristics of the building blocks of multiscale methods, first a brief review of some significant computational methods at individual length and time scales is provided. These methods cover quantum mechanical scale, atomistic domain (Monte Carlo and molecular dynamics), mesoscopic scale (Brownian dynamics, dissipative particle dynamics, and lattice Boltzmann method), and finally macroscopic realm (finite element and volume methods). Afterwards, different prescriptions to envelope these methods in a multiscale strategy are discussed in details. Sequential, concurrent, and adaptive resolution schemes are presented along with the latest updates and ongoing challenges in research. In sequential methods, various systematic coarse-graining and backmapping approaches are addressed. For the concurrent strategy, we aimed to introduce the fundamentals and significant methods including the handshaking concept, energy-based, and force-based coupling approaches. Although such methods are very popular in metals and carbon nanomaterials, their use in polymeric materials is still limited. We have illustrated their applications in polymer science by several examples hoping for raising attention towards the existing possibilities. The relatively new adaptive resolution schemes are then covered including their advantages and shortcomings. Finally, some novel ideas in order to extend the reaches of atomistic techniques are reviewed. We conclude the review by outlining the existing challenges and possibilities for future research.

Atomistic Modelling of Confined Polypropylene Chains between Ferric Oxide Substrates at Melt Temperature

The interactions and conformational characteristics of confined molten polypropylene (PP) chains between ferric oxide (Fe2O3) substrates were investigated by molecular dynamics (MD) simulations. A comparative analysis of the adsorbed amount shows strong adsorption of the chains on the high-energy surface of Fe2O3. Local structures formed in the polymer film were studied utilizing density profiles, orientation of bonds, and end-to-end distance of chains. At interfacial regions, the backbone carbon-carbon bonds of the chains preferably orient in the direction parallel to the surface while the carbon-carbon bonds with the side groups show a slight tendency to orient normal to the surface. Based on the conformation tensor data, the chains are compressed in the normal direction to the substrates in the interfacial regions while they tend to flatten in parallel planes with respect to the surfaces. The orientation of the bonds as well as the overall flattening of the chains in planes parallel to the solid surfaces are almost identical to that of the unconfined PP chains. Also, the local pressure tensor is anisotropic closer to the solid surfaces of Fe2O3 indicating the influence of the confinement on the buildup imbalance of normal and tangential pressures.

Rheological properties of wood polymer composites and their role in extrusion

The influence of the rheological behaviour of PP based wood plastic composites (WPC) has been investigated in this research by means of a high pressure capillary rheometer incorporating dies having different geometries. The rheological experiments were performed using slit and round dies. The influence of moisture content on the flow properties of the WPC has been investigated as well. It was observed that higher moisture contents lead to wall slippage effect. Furthermore, measured viscosity data have been used in flow simulation of an extrusion profile die. Also, the influence of different rheological models on the simulation results is demonstrated. This research work presents a theoretical and experimental study on the measurement and prediction of the die pressure in the extrusion process of wood-plastic composite (WPC).

Multiscale Simulation of Polymer Nanocomposites in Processing: Challenges and Outlooks

This paper attempts to address current possibilities in the multiscale simulation of polymer nanocomposites (PNCs) in processing. To provide a comprehensive perspective, a number of PNCs were produced by the incorporation of nanoclays in different polymer matrices. The microstructure evolutions of the simulated counterparts of such systems were studied with and without shear flows in a dissipative particle dynamics (DPD) framework spanning from several nanometers up to a few microns. Transmission electron microscopy (TEM) was utilized to contrast the simulations against the actual nanocomposites. A satisfactory precision was achieved in the build-up of the simulated structures. A significant characteristic of anisometric particles was studied, namely the orientation of the particles due to the imposed flows. It was shown that the orientation of such particles could be well described. Finally, opportunities were addressed for the simulations to carry on to the higher scales.

Dissipative particle dynamics simulations of orientation of layered silicate particles embedded in polymer melts under shear flows

Orientation of anisometric layered silicate particles subject to shear flows has always been a crucial factor in the final microstructure of polymer nanocomposites in polymer processing. Plenty of experimental works and theoretical investigations have been conducted in order to provide an accurate understanding of the phenomena involved. The development of coarse-grained molecular simulation methods in recent years has made it possible to explore more details of pre-described systems under a variety of conditions. Dissipative particle dynamics (DPD) being one of them, has been widely applied to study multicomponent materials. With the introduction of Lees-Edwards boundary conditions, DPD was soon found to be an efficient method to simulate hydrodynamic systems considering its ability to access longer time scales compared with classic molecular dynamics. Here, we report on the orientation of a semi-flexible 3-layered silicate particle embedded in a polymer matrix while imposed to shear flows. By applying d...

Numerical simulations of the flow of wood polypropylene composites with wall slipping in a profile die: The significance of material data

This paper demonstrates the importance of the careful selection of the input material data for the calculation of the flow behavior of wood polypropylene composites. To this goal, the rheological data of un-dried samples were measured, utilizing a commercial high pressure capillary rheometer equipped with slit dies of different gap heights. The data were incorporated in finite-difference and finite-element methods in order to predict the pressure drop along a profile die and compared to measurements on an extruder at different flow rates.While the un-dried sample is expected to undergo wall slippage during flow, the simulation results on the slit and profile dies indicate that neither a fully slipping plug flow nor a fully adhering shear flow is capable of providing reasonable results. By utilizing ANSYS Polyflow software, a combination of both flow types was incorporated in a 3-dimensional FEM analysis to simulate the pressure drops. The results show that by using the shear viscosity data from capillary ...