Dissipative Particle Dynamics (DPD) has shown a great potential in studying the dynamics and rheological properties of soft matter; however, it is associated with deficiencies in describing the characteristics of entangled polymer melts. DPD deficiencies are usually correlated to the time integrating method and the unphysical bond crossings due to utilization of soft potentials. One shortcoming of DPD thermostat is the inability to produce real values of Schmidt number for fluids. In order to overcome this, an alternative Lowe-Anderson (LA) method, which successfully stabilizes the temperature, is used in the present work. Additionally, a segmental repulsive potential was introduced to avoid unphysical bond crossings. The performance of the method in simulating polymer systems is discussed by monitoring the static and dynamic characteristics of polymer chains and the results from the LA method are compared to standard DPD simulations. The performance of the model is evaluated on capturing the main shear flow properties of entangled polymer systems. Finally the linear and nonlinear viscoelastic properties of such systems are discussed.

Dissipative particle dynamics (DPD) is a well-known simulation method for soft materials and has been applied to a variety of systems. However, doubts have been cast recently on its adequacy because of upper coarse-graining limitations, which could prevent the method from being applicable to the whole mesoscopic range. This paper proposes a modified coarse-grained level tunable DPD method and demonstrates its performance for linear polymeric systems. The method can reproduce both static and dynamic properties of entangled linear polymer systems well. Linear and non-linear viscoelastic properties were predicted and despite being a mesoscale technique, the code is able to capture the transition from the plateau regime to the terminal zone with decreasing angular frequency, the transition from the Rouse to the entangled regime with increasing molecular weight and the overshoots in both shear stress and normal-stress differences upon start-up of steady shear.

Colloidal suspensions exhibit a transition from shear-thinning to shear-thickening behavior as the shear rate increases. Despite all the experimental and computational studies, an understanding of the structure of suspensions in different flow regimes remains controversial. In this work, a dissipative particle dynamics model was employed to perform a comprehensive study of the rheological and morphological behaviors of monodisperse and bimodal suspensions over a wide range of shear rates.The interplay between rheology and structure indicates that hydroclusters are formed in the shearthickening regime, whereas interparticle interaction is responsible for the shear-thinning response at low stresses. The effect of particle size, ratio, and combination in bimodal systems have also been investigated and quantitative agreement with existing experimental data was found. Thus, it was possible for the first time to perform a comprehensive study on different aspects of the bimodal dispersions and correlate the macroscopic behavior with the microstructure in different flow regimes.

In this work, a generalized relation between the fluid compressibility, the Flory-Huggins interaction parameter (χ), and the simulation parameters in multi-body dissipative particle dynamics (MDPD) is established. This required revisiting the MDPD equation of state previously reported in the literature and developing general relationships between the parameters used in the MDPD model. We derive a relationship to the Flory-Huggins χ parameter for incompressible fluids similar to the work previously done in dissipative particle dynamics by Groot and Warren. The accuracy of this relationship is evaluated using phase separation in small molecules and the solubility of polymers in dilute solvent solutions via monitoring the scaling of the radius of gyration (Rg) for different solvent qualities. Finally, the dynamics of the MDPD fluid is studied with respect to the diffusion coefficient and the zero shear viscosity.

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