Molecular Dynamics Study on the Deformation Behaviors of Nanostructures in the Demolding Process of Micro-Injection Molding

Abstract

Polymer parts with nanostructures have broad applications, possessing excellent optical, electrochemical, biological, and other functions. Injection molding technology is one of the main methods for mass production of polymer parts with various shapes and sizes. The demolding process is vital to the replication quality of molded parts with nanostructures. For this study, molecular dynamics simulations of polypropylene (PP), polymethyl methacrylate (PMMA), and cycloolefin copolymer (COC) were conducted for the demolding process. The average velocity, density distribution, adhesion energy, and demolding resistance were introduced to analyze the deformation behaviors of polymer nanostructure from a nickel nano-cavity with an aspect ratio of 2:1. The shoulders of nanostructures were firstly separated from the nickel mold insert in the simulation. Under the external demolding force of 0.07 nN, PP and PMMA could be successfully demolded with some deformations, while COC could not be completely demolded due to the greater adhesion energy between COC and Ni. It was found that the maximum adhesion energy occurred in the separation process between the shoulder of the nanostructure and Ni and the huge adhesion energy was the main cause of demolding defects. The velocity difference of the whole polymer layer and polymer nanostructure was further analyzed to explain the nanostructure deformation. In order to improve the quality of demolding, the external force applied on polymers should be properly increased.

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

“…Previous studies have shown that the polymerization degree has a significant impact on the filling capacity [35]. Nevertheless, in order to observe the separation of nanostructure from nanocavity during the demolding process, a low polymerization degree was set to allow the molecular slippage and disentanglement under the external demolding force [33]. Then, 130 chains were randomly generated to construct the amorphous polymer system with a box size of 5.0 × 5.0 × 7.9 nm.…”

“…At present, the MD method has been widely applied to most of the research areas, such as the nanoimprint lithography technology [21,22,23], the micro-injection molding technology [24,25,26], the direct injection joining technology [27,28], the calculation of interfacial adhesion [29,30], and the simulation of self-assembled monolayer [31]. For the study of polymer molding, the MD method was mainly used by researchers to analyze the influences of nanostructure shapes [22,23,27,32], the mold insert and polymer materials [30,33], the anti-stick treatment of surface [32,34], the processing parameters [26,32], and other factors on the molding qualities. However, the above studies mainly focus on the nanoimprint lithography technology, and there are few reports on the micro-injection molding.…”

Influence of Diamond-Like Carbon Coating on the Channel Deformation of Injection-Molded Microfluidic Chips during the Demolding Process

“…The molecular chains at the shoulders and bottom were most severely stretched along the z-direction for the demolding deformation of the PC channel. The deformations of the COC channel mainly included stretched molecular chains, elongated structure and serious surface burrs [26]. While the PS and PMMA channels with good demolding quality basically remained their geometrical shapes after demolding, as shown in Figure 2a In order to study the influence of DLC coating on the demolding quality of injection-molded microfluidic chips, the demolding process of four polymer channels on the Ni mold insert treated with DLC coating was simulated by the MD simulation method, as shown in Figure 3.…”

“…Thus, it is very important to further study the interfacial interactions in the fabrication of polymer microstructures from the molecular or atomic level. Molecular dynamics (MD) simulation methods for the analysis of interfacial interactions have been widely applied in nanoimprint lithography (NIL) [22,23], interfacial mechanisms [24,25], polymer injection molding [26,27], pulling simulations in diverse molecular systems [28,29] and other fields, which can accurately analyze the interaction mechanism of polymer-mold insert during the polymer molding process. Hsu et al [30,31] used the MD method to study the influences of temperature, the aspect ratio of the stamp, and the anti-sticking layer on the polymer molding quality in the NIL process.…”

Molecular dynamics simulation on the adhesion mechanism at polymer‐mold interface of microinjection molding

“…20,21 From the literature reports, MD simulation method has been widely applied in many research fields, such as nanoimprinting, 17,22,23 bonding mechanism, 24,25 composite materials, [26][27][28] and molecular self-assembly. 29 On the other hand, MD simulation method has been successfully used by researchers to explore the filling mechanism, 30,31 the demolding mechanism, 32 and the molding quality 33 of nanostructures in injection molding. However, the adhesion mechanism at the polymer-mold interface has not been reported in the related literature.…”