The Lowe-Andersen thermostat as an alternative to the dissipative particle dynamics in the mesoscopic simulation of entangled polymers

Abstract

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.

Viscosity measurement techniques in Dissipative Particle Dynamics

“…An increase of the temperature under strong non-equilibrium conditions is a well-known phenomenon that has been studied extensively and different thermostats have been proposed to address the issue [8,9]. As one can clearly conclude from Fig.…”

“…Whittle and Travis [8] studied different external (MD-based) thermostats and their performance on controlling the temperature of a colloidal suspension under shear. Khani et al [9] studied the temperature controlling effect of so-called LoweAnderson thermostat as an alternative to traditional DPD forces in polymer melts and found better stability of both temperature and dynamics using this method when compared to the simple dissipative-random ensemble. However, they have shortcomings at predicting the transport properties.…”

“…Different groups have studied rheological behavior of suspensions using both traditional and modified DPD [11][12][13][14][15]. Polymer melts and solutions, as well as multiphase systems have also been studied with special emphasis on their rheological behavior using DPD [9,16,17]. However, one can conclude from a careful review of the prior publications that, even for the simplest system (water, first studied by Groot and Warren [2]), values reported for the viscosity vary from one report to another, depending on the type of flow and method used for calculation of viscosity, boundary conditions and the choice of force parameters [17][18][19][20].…”

Gaussian-inspired auxiliary non-equilibrium thermostat (GIANT) for Dissipative Particle Dynamics simulations

“…Different thermostats and alternatives have been proposed in efforts to fix the temperature controlling effect in DPD at rest (equilibrium conditions) [27,28]. The reason for this is that increasing the time-step in simulation of viscoelastic fluids with DPD even at rest (no-flow) can be problematic [29].…”

“…The level of shear rates required for simulation of a fluid varies from one to another based on the fluid characteristics and the subject of the study. For instance, in order to study the dynamics of polymer melts under flow, one needs low/intermediate shear rates as this value is strictly dictated by the length scales appropriate for polymer chains [27]. On the other hand, much higher values of shear rates are required when rheology of sheared colloidal suspensions are studied.…”