Calculation of the work of adhesion of polyisoprene on graphite by molecular dynamics simulations

Elastomeric compounds are reinforced with fillers such as carbon-black and silica to improve mechanical, dynamical, and tribological properties. The stability and physical properties of these materials are dominated by the intermolecular interactions occurring at the polymer/particles interface that determine the magnitude of the polymer/particles adhesion. Using molecular dynamics simulations, in this work, we evaluate the solid–liquid interfacial tension and the corresponding work of adhesion for a system composed of graphite/Polyisoprene 100% cis-1,4 within a range of molar masses and temperatures. We employ a simulation strategy for estimating the surface tension of fluid/vacuum and fluid/solid interfaces that use directly the local stress fields in the Irving–Kirkwood formalism. Using such procedure, we decompose the stress field into the individual components of the stress tensor and correlate them with the values of the work of adhesion in the different systems analyzed

Rigidity of plasticizers and their miscibility in silica-filled polybutadiene rubber by broadband dielectric spectroscopy

An efficient use of plasticizers in rubber compounds requires an understanding of their miscibility behavior. Besides the chemical properties of both rubber and plasticizer, the rigidity of the plasticizer plays an important role for their miscibility. The miscibility is investigated here using the glass transition measured by differential scanning calorimetry and broadband dielectric spectroscopy (BDS). Additionally, the interfacial relaxation and phase separation measured by BDS are confirmed by transmission electron microscopy. While the flexible plasticizer, poly-(α-methylstyrene), stays miscible in a silica-filled polybutadiene rubber compound, the more rigid plasticizer, indene-coumarone (IC), shows a phase separation at high concentrations. The phase-separated IC tends to accumulate at the silica surface

CFD-DEM characterization and population balance modelling of a dispersive mixing process

This work investigates the breakup dynamics of solid agglomerates in a polymer compounding operation, by using computational fluid dynamics (CFD) simulations together with discrete element method (DEM) simulations. CFD simulations are used to compute the flow field and the shear stress distribution inside a 2D section of a typical internal mixer for polymer compounding. DEM simulations are instead used to predict the mechanical response of the agglomerates and to detect the critical viscous shear stress needed to induce breakup. DEM breakup data and viscous stress distributions are correlated by a first–time passage–statistics and used to calibrate a population balance model. The work returned detailed insights into the flow field characteristics and into the dispersive mixing kinetics. The simulation strategy herein reported can be adapted to study generic solid–liquid disperse flows in which the breakup of the solid phase is found at the core of the system behaviour

A CFD-DEM approach to study the breakup of fractal agglomerates in an internal mixer

In this work we present a method to investigate the breakup of filler agglomerates in an internal mixer during a compounding operation. The method employs computational fluid dynamics (CFD) simulations along with discrete element method (DEM) simulations. CFD simulations are performed to compute the flow field inside a 2D section of a typical batch internal mixer with two tangential rotors. During the CFD simulation, we assume the filler agglomerates to behave as tracer particles, carried passively by the flow. The trajectory of the tracers, together with the experienced velocity gradients, are fed to a DEM code, built in the framework of Stokesian dynamics. The code computes the mechanical response of the agglomerates along the trajectory, from which it is finally possible to ascertain the occurrence of breakup. Simulations are performed to evaluate the robustness of the method on two different rotor speed ratio conditions and varying agglomerate strength

Multiscale Simulation Methods for Polymers

Computer simulations of condensed phases and biochemical systems have lead to profound new insight into molecular-scale phenomena occurring in these complex systems. Many processes that occur in liquids, soft materials, and biochemical systems however occur over length and time scales that are well beyond the current capabilities of atomic-level simulations. In the field of polymers, there are many simulation techniques and models that span a range from the atomistic scale to the continuum. In recent years, much research has been focused on linking models of different length scales, especially from detailed, fully atomistic to mesoscopic scales and back. A common way of addressing this issue is to develop coarse-grained (CG) models from full-atomistic simulations by merging groups of chemically connected atoms into superatoms. This PhD thesis describes new developments in the field of CG simulations of polymers. In addition to CG simulations, atomistic molecular dynamics calculations are performed as well to study properties of polymers