Molecular Dynamics Simulation Of Polymer Melts Flow In Nanochannel

With the development of science and technology, natural science and engineering technology are innovating towards miniaturization and nanotechnology. The micro/nano electro mechanical systems and micro/nano fluidic systems have a wide development and application prospect in the fields of modern industry, biological engineering and information technology. Many theoretical and technical problems about the manufacturing of micro scale components and the flow process of micro/nano fluid have not been effectively resolved due to micro scale factors influence. There is a lack of comprehensive and profound understanding about the flow behaviors, the morphology of molecular chains and the microcosmic mechanism of the influence factors for Non-Newtonian polymer melt in nano scale channel, which are the key problems for micro system technology development and the application of micro-fluidic devices. So in order to promote the development of micro/nano technology, it is of great significance to study the micro flow behaviors of long chain polymer in nano scale channel, to explore the effect mechanism of different factors on the dynamics properties of long chain molecules in flow field, and to reveal the law of the fluid flow in micro/nano scale channel.Based on the comprehensive understanding about the research status of flow theory and application research of micro/nano scale fluid and also based on the theory of polymer rheology, the Poiseuille flow behaviors of long chain polymer in the nano scale channels are simulated in this paper using molecular dynamics simulation methods and the bead-spring model. How the molecular chain length, the external force, the wall wettability, the height of channel and temperature of polymer melts affect the flow properties of polymer, how the channel roughness affects the flow properties of polymer and how the ultrasonic wave enhances the flow of polymer melts are studied. The information of velocity field, density field, transport property, and structure changing are traced on base of the simulations to reveal the dynamics properties and structure properties of polymer melts.The study results of the influence of polymer chain length, external force, wall wettability, channel height, and polymer temperature on flow process show as follows:①The polymer diffusion ability, the radius of gyration and the orientation of polymer chain in x-direction increase with the increasing of chain length.②The external force dramatically has influence on the flow velocity field. With the increasing of external force, the polymer flows in three regions (free molecule oscillation region, coupling region and gravity force domain region), and the diffusion ability of polymer melts increases. A larger external force can help polymer melts form stronger orientation in the force direction.③For hydrophilic wall, the velocity decreases and the slip boundary phenomenon disappears. With the increasing wall-fluid interaction binding parameter, the diffusion coefficient values both in the bulk and near the wall decrease linearly.④The channel width affects the molecular morphology mostly. The molecules are in limited space when the channel height is smaller than the radius of gyration.⑤For FENE polymer melts in nanochannel, a little change of the polymer temperature does not make much difference to the flow process.The study results of the influence of wall roughness on flow process show as follows: When the channel surface is rough, the polymer velocity field and density field are no longer symmetric. The roughness of wall may lead to the disappearing of slip phenomenon and the decrease of diffusion parameter. The flow of polymer melts is impeded by the rough wall, and the polymer chains at the wall show some special flow phenomena.The study results of the influence of the ultrasonic wave on flow process show that the flow velocity of the polymer melts increases under the effect of the ultrasonic wave. The polymer diffusion capacity increases, and the values of the radius of gyration and the orientation of polymer chains increase. The ultrasonic wave can promote the flow of polymer melts.