Molecular Dynamics Simulation on the Influences of Nanostructure Shape, Interfacial Adhesion Energy, and Mold Insert Material on the Demolding Process of Micro-Injection Molding

Jin Yang,Hao Wang,Jun Lai,Can Weng,Tao Ding

doi:10.3390/polym11101573

Jin Yang, Hao Wang + Show 3 more

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https://doi.org/10.3390/polym11101573

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Abstract

In micro-injection molding, the interaction between the polymer and the mold insert has an important effect on demolding quality of nanostructure. An all-atom molecular dynamics simulation method was performed to study the effect of nanostructure shape, interfacial adhesion energy, and mold insert material on demolding quality of nanostructures. The deformation behaviors of nanostructures were analyzed by calculating the non-bonded interaction energies, the density distributions, the radii of gyration, the potential energies, and the snapshots of the demolding stage. The nanostructure shape had a direct impact on demolding quality. When the contact areas were the same, the nanostructure shape did not affect the non-bonded interaction energy at PP-Ni interface. During the demolding process, the radii of gyration of molecular chains were greatly increased, and the overall density was decreased significantly. After assuming that the mold insert surface was coated with an anti-stick coating, the surface burrs, the necking, and the stretching of nanostructures were significantly reduced after demolding. The deformation of nanostructures in the Ni and Cu mold inserts were more serious than that of the Al2O3 and Si mold inserts. In general, this study would provide theoretical guidance for the design of nanostructure shape and the selection of mold insert material.

Highlights

In recent years, micro/nanostructured products have been applied and developed in many fields, such as biomedical, aerospace, clean energy, and electronic communication [1,2,3,4]
The molecular dynamics (MD) simulation method was used to simulate the demolding process of micro-injection molding for rectangular, trapezoidal, and tapered nanocavities
Under the same external demolding force, the rectangular nanostructure could retain most of its original morphology after demolding, while the trapezoidal and tapered nanostructures were severely deformed, and the original morphologies were almost disappeared

Summary

Introduction

Micro/nanostructured products have been applied and developed in many fields, such as biomedical, aerospace, clean energy, and electronic communication [1,2,3,4]. Micro-injection molding technology, due to its low cost and high efficiency, is regarded as one of the most promising manufacturing methods for micro/nanostructures. It mainly includes four stages as the injection, the packing, the cooling, and the demolding [5,6]. The demolding stage is crucial for the high-precision replication of nanostructured parts, which directly affects the function and characteristics of the products [7,8,9]. Most of the defects are significantly caused by the adhesion and friction of the polymer-mold insert interface [9,12]. In order to reduce the adhesion between the mold insert and Polymers 2019, 11, 1573; doi:10.3390/polym11101573 www.mdpi.com/journal/polymers

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