Molecular dynamics simulation of injection of polyethylene fluid in a variable cross-section nano-channel

Abstract

Numerical simulation of injection of polyethylene fluid in a variable cross-section nano-channel was carried out using the molecular dynamics method. The effects of the nano-channel cross-section and the external force on the rheological behavior and structural properties of the polyethylene fluid were investigated. It was found that an absorbed layer appeared near the wall and the thickness of the absorbed layer increased with increasing cone angle of the nano-channel. The injection distance of the polyethylene fluid decreased with increasing cone angle and decreasing external force. In the nano-channel with cone angle 45°, polyethylene particles uniformly filled the whole channel and were stretched along the flow direction. Uniaxial stretching of particles was enhanced when the external force was strengthened, which facilitates injection of the polyethylene fluid into the nano-channel. molecular dynamics simulation, polyethylene, injection process, nano-channel Citation:Feng J, Liao Q, Zhu X, et al. Molecular dynamics simulation of injection of polyethylene fluid in a variable cross-section nano-channel. Chinese Sci Bull, 2011Bull, , 56: 1848Bull, −1856Bull, , doi: 10.1007 With the development of nano-manufacturing, the technologies of precise distribution and delivery have been applied to a multitude of areas such as medical and biochemical engineering. Nano-injection systems, e.g. the nano-injector with an electromagnetic micro pump [1], nano-injection for capillary gas chromatography [2] and injection of ceramic bodies in nano-channels [3], have received much attention [4,5]. Injection molding of polymers is also utilized in many areas [6,7]. A polymer fluid exhibits unusual viscoelastic behavior in a nano-channel because of the topological constraints [8,9], so the process of polymer injection should be precisely controlled. The variation of any operating condition, such as temperature, viscosity, injection speed and pressure, can change the fluid properties of a polymer and destroy the injection process. Thus the complex *Corresponding author (email: lqzx@cqu.edu.cn) behavior of polymer flow in nano-channels should be fully understood. Molecular dynamics simulations avoid the difficulties of experimental investigation, and have become an effective tool in analyzing the rheological behavior of polymer fluids. Several researchers [10][11][12] have employed non-equilibrium molecular dynamics simulations to understand the properties of polymer fluids in Couette shear flow. One can distinguish from literatures three models, namely the dumbbell model [13], the freely jointed chain model [14] and the Rouse model [15], to simplify the structures of the polymer chains. In the dumbbell model two beads that represent the molecular segments of several monomers are connected by a Hookean spring, which denotes the entropic effects on the end-to-end vector of the polymer. The freely jointed chain model depicts the polymer as a chain consisting of segments; the orientation of a segment is totally independent of

Filling of Irregular Channels with Round Cross-Section: Modeling Aspects to Study the Properties of Porous Materials

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