Progressive Molecular Rearrangement and Heat Generation of Amorphous Polyethene Under Sliding Friction: Insight from the United-Atom Molecular Dynamics Simulations

Abstract

Frictional heat has been widely used in various polymer-based advanced manufacturing. The fundamental understanding of the thermodynamics of the interfacial friction of polymer bulk materials can help to avoid compromising the process controllability. In this work, we have performed unitedatom molecular dynamics (MD) simulations to reveal the interfacial friction heating mechanism of amorphous polyethene (PE) in both the single sliding friction (SSF) and reciprocating sliding friction (RSF) modes. Different from the traditional view that the plastic deformation was the primary source of heat generation, the RSF process with no apparent plastic deformation in this work shows a better heat generation performance than SSF, where plastic deformation dominated the friction process. Our analysis uncovers that the mechanism of the interfacial friction heating enhancement in RSF can be attributed to the concentrated high-frequency chain motion related to molecular rearrangement, which is not clearly related to the deformation degree.

Molecular Dynamics Study of the Dispersion Stability and Fluidity of Porous Liquids with Different Canopy Structures

“…The glass state is a nonequilibrium state in thermodynamics. T g is often calculated in the cooling process from high temperatures to low temperatures. , In our simulations, the “cooling process” was divided into 10 equilibrium molecular dynamics at temperatures of 350, 340, 330, ..., 240, and 230 K. For example, in the PL M2070 system, 3 ns NVT ensemble dynamics at 310 K was carried out and the last 500 ps NVT simulation was for data sampling to average the nonbond energy. The final configuration was used as the starting structure for dynamics at 300 K and so on.…”

Tuning Power Ultrasound for Enhanced Performance of Thermoplastic Micro-Injection Molding: Principles, Methods, and Performances

“… ( a ) Changes in temperature as a function of time in SSF and RSF modes; ( b ) Friction simulation results of PE internal structure under two friction modes at the same simulation time point; Variation of chain orientation parameters with sliding time in the SSF process ( c ) and the RSF process ( d ) [ 152 ]. …”

“… Variation of PE bulk temperature with time in RSF mode under ( a ) various loading pressures and ( b ) various frequencies [ 152 ]. …”

“…The regularization of production materials may become one of the important development directions of this process. Subsequently, Wu et al [152] performed united-atom molecular dynamics simulations to reveal the interfacial friction heating mechanism of amorphous polyethylene under single sliding friction (SSF) and reciprocating sliding friction (RSF) modes. The results show that RSF is a more efficient way of generating heat than SSF in terms of heating as shown in Figure 28a; that is, ultrasonic plasticization is the one with higher heating efficiency.…”

“…In terms of orientation, the molecular chain in the RSF model is disordered due to the frictional form of highfrequency vibration restricted in its region, as shown in Figure 28d. Therefore, the concentrated high-frequency chain motion related to molecular rearrangement is Subsequently, Wu et al [152] performed united-atom molecular dynamics simulations to reveal the interfacial friction heating mechanism of amorphous polyethylene under single sliding friction (SSF) and reciprocating sliding friction (RSF) modes. The results show that RSF is a more efficient way of generating heat than SSF in terms of heating as shown in Figure 28a; that is, ultrasonic plasticization is the one with higher heating efficiency.…”