Orientation of Anisometric Layered Silicate Particles in Uncompatibilized and Compatibilized Polymer Melts Under Shear Flow: A Dissipative Particle Dynamics Study

Abstract

The orientation of a three‐layered silicate particle in uncompatibilized and compatibilized polymer melts is studied under shear flows utilizing dissipative particle dynamics (DPD). Based on trajectories, pair distribution functions are calculated in orthogonal planes. Regardless of the applied flow direction, it is shown that the layers rearrange themselves so that their surfaces would be normal to the velocity gradient direction. The maximum shear stress values fall in numerical uncertainties in uncompatibilized systems while they show a characteristic overshoot in compatibilized counterparts. This overshoot is shown to be a result of (i) the large interfaces between the silicate layers and the matrix due to the exfoliation, and (ii) the increased energy dissipation due to friction at the interface.

Dissipative Particle Dynamics Models of Orientation of Weakly‐Interacting Anisometric Silicate Particles in Polymer Melts under Shear Flow: Comparison with the Standard Orientation Models

“…These values were 33 and 15 for polymer–silicate and silicate–silicate, respectively. We showed before that these values can provide an accurate representation of the orientation in such systems . The friction coefficients were 5.6 for interactions between polymer–silicate and silicate–silicate pairs, and 4.5 for polymer–polymer pairs ,…”

“…The shear‐rate was set to 0.1 (in DPD units) in all simulations. This value was selected to avoid thermal fluctuations that could distort the velocity profile at very low shear‐rates, and the overwhelming of the thermostat at very high shear‐rates due to the energy dissipations …”

“…It was shown that the reverse Poiseuille flow yields more complete rheograms than those computed from conventional Lees–Edwards Couette flow particularly near the zero‐shear‐rate plateaus. In spite of these attempts, DPD still suffers from the intrinsic instabilities at very low or very high shear‐rates and needs further improvements . In order to capture reptational dynamics of long polymer chains in DPD, Nikunen et al used simple topological constraints to prevent bond crossings.…”

“…In a recent study, we incorporated DPD models to predict the orientation of semiflexible‐layered silicate particles in uncompatibilized and compatibilized polymer melts under various shear flows . The model could successfully capture the orientation of such anisometric particles.…”

Coupled Orientation and Stretching of Chains in Mesoscale Models of Polydisperse Linear Polymers in Startup of Steady Shear Flow Simulations

“…Moreover, at very low shear-rates the deviations from the applied linear velocity profi le leads to local fl ow heterogeneities. [ 23,26,34 ] Such distortions would impose strong numerical uncertainties in the calculations. Therefore, it is important to note such effects when studying the effects of very low and very high shear-rates on the response of the systems.…”