Wall Slip Behaviour of Polymers Based on Molecular Dynamics at the Micro/Nanoscale and Its Effect on Interface Thermal Resistance.

Yan Lou,Gang Wu,Yanfeng Feng

doi:10.3390/polym12102182

Abstract

Taking the Poiseuille flow of a molten polymer in parallel plates as the research object and polymethyl methacrylate (PMMA) as the research material, an all-atom analysis model of the molecular dynamic flow of polymer macromolecules is established according to the Navier slip law. The effects of wall wettability and external pressure on the wall slip behaviour of polymer macromolecules, as well as the spatial evolution process of the entanglement–unentanglement process of polymer chains near the wall under different shearing effects, were studied. The interface thermal resistance rule was explored, and an interface thermal resistance model considering the wall slip behaviour was established. Finally, a micro-injection experiment was used to verify the validity and accuracy of the model. The results show that when the wall is hydrophobic, the polymer melt exhibits significant wall slip. As the external pressure increases, the wall slip speed and the slip length increase. However, after a certain pressure is exceeded, the growth rate of the slip length is basically zero. As the external pressure increases, the PMMA molecular chains gradually start to separate, the single molecular chain becomes untangled from the entangled grid, and the chain detaches from the wall after exceeding a certain threshold. Wall slip reduces the interface thermal resistance between the solid–liquid interface and enhances the interface heat transfer performance. The interface thermal resistance value calculated by molecular dynamics can more accurately reflect the heat conduction rule of the solid–liquid interface at the micro/nanoscale than that measured by the thermal resistance experiment, indicating that the micro/nano interface thermal resistance obtained by molecular dynamics simulation is reliable.

Highlights

Micro/nano-injection moulding increases the surface-to-body ratio of micro/nanoscale cavities, which intensifies the heat transfer at the solid–liquid interface and leads to rapid cooling of a melt.Wall slip and thermal contact resistance (TCR) are important boundary parameters in numerical simulations, and they determine the accuracy of micro/nano-injection moulding simulations.Many scholars have begun to use molecular dynamics (MD) simulations to study the wall slip phenomenon
Martini et al [1] used MD to simulate the wall slip length and found that there is a threshold at a higher shear rate; the slip length does not change after exceeding this value
To obtain the TCR value between the solid–liquid interface, it is necessary to measure the mould calculated by the temperature recorded by the thermocouple

Summary

Introduction

Micro/nano-injection moulding increases the surface-to-body ratio of micro/nanoscale cavities, which intensifies the heat transfer at the solid–liquid interface and leads to rapid cooling of a melt.Wall slip and thermal contact resistance (TCR) are important boundary parameters in numerical simulations, and they determine the accuracy of micro/nano-injection moulding simulations.Many scholars have begun to use molecular dynamics (MD) simulations to study the wall slip phenomenon. Micro/nano-injection moulding increases the surface-to-body ratio of micro/nanoscale cavities, which intensifies the heat transfer at the solid–liquid interface and leads to rapid cooling of a melt. Wall slip and thermal contact resistance (TCR) are important boundary parameters in numerical simulations, and they determine the accuracy of micro/nano-injection moulding simulations. Many scholars have begun to use molecular dynamics (MD) simulations to study the wall slip phenomenon. Martini et al [1] used MD to simulate the wall slip length and found that there is a threshold at a higher shear rate; the slip length does not change after exceeding this value. Bendada et al [2] reported that in the early stage of injection moulding, polymer macromolecular chains produced tensile orientation deformation under the action of flow-induced stress. In the later stage of mould filling, as the orientation deformation time was prolonged, the molecular chains unwrapped

Methods

Results

Conclusion