Molecular Simulation Study Of Fluid Transport In Biomimetic Carbon Nanochannels

Since ancient times,nature has always been the source of inspiration of human design principles and inventions.In cell membranes of organisms,there are varieties of biological channels,and most of these channels are selective and have environmental responsiveness.They play an important role in regulating the exchange of materials and energy inside and outside cells.According to the relationship between the structure and function of the biological channels,it is of great interest to biomimetic design of artificial nanochannels with functions close to the biological channels.The designed artificial channels are expected to have great potentials in controlling the transport behavior of the nanoscale fluid and designing functionalized nanofluidic devices in further.However,limited by the current experimental preparation techniques,the size of the biomimetic channels is usually larger than 5 nm,whereas the size of the channels in biofilms is mostly at the sub-nanometer level(sub-2 nm).Therefore,studying the biomimetic design of sub-nanoscale channels and the corresponding transport behavior of fluids in these channels have great significances for the theoretical development and pratical applications of nanofluid.In this thesis,using carbon nanomaterials as templates,molecular simulation method was adopted to study the biomimetic design of subnanoscale carbon nanochannels based on the relationship between the structure and function of biological water and ion channels,and the mechanisms for the designed carbon nanochannel regulating fluid transport were then revealed.These studies provide an important theoretical guidance for the understanding and design of functionalized artificial nanochannels.The main research contents in this thesis are summarized below.The water channels in cell membranes have conical channel structure that enables efficient transport of water molecules across the membrane.Based on this structure and function relationship,molecular dynamics(MD)simulation was used to study the scrolling behavior of tailored graphene flakes.Through regulating the tailoring patterns,we provided a method to form conical nanochannels via graphene scrolling.Then,the transport behavior of water molecules in conical carbon nanochannels was studied,and the ability of the conical carbon nanochannels regulating water transport was clearly defined.Finally,the structure of the conical carbon nanochannel was further designed to achieve the function of high efficient water desalination.The ion channels in cell membranes have the function similar to crystal diode.They have the ability to rectify ion current.Previous studies have provided that ion current rectification function of biological ion channel is the result of the interaction between its conical channel structure and the charged channel inner surface.Based on this structure and function relationship,a conical carbon nanochannel with the function of ion current rectification was designed by MD simulation.It was found that the conduction direction of ion current for the conical carbon nanochannel was opposite to that of conical nanochannels prepared in experiment.Compared with the experimental studies,we inferred that the scale effect was the main reason for the opposite rectification phenomenon.In addition,by observing the microscopic ion transport process in our conical carbon nanochannels,a special ion transprot mode,which was similar to the Coulombic knock-on ion transport mode observed in biological ion channels,was found.The internal structure of biological channels is very complex,and most of them have threedimensional(3D)structural features.Previous studies showed that the 3D structural features of biological channels have certain regulation ability on the molecular transport in them.According to this structure and function relationship,one spiral graphene nanochannel was designed by using MD simulation.Meanwhile,the biological channels are usually embedded in phospholipid bilayers.The phospholipid bilayer incessant vibrates throughout the life of cell,which in turn drives the vibration of biological channels and affects the corresponding molecular transport.According to this structure and function relationship,we controlled the vibration properties of the designed spiral graphene nanochannels during the simulations and studied the influence of channel vibration on the molecular transport.The results showed that the channel vibration could accelerate the molecular transport,whereas the spiral channel had a low molecular transport rate due to its smaller effective pore size and longer molecular transport pathways compared with non-spiral channel.Howerver,the spiral channel had special function for molecular separation of chiral amino acid molecules.Furthermore,we also studied the influence of length and pore size of graphene nanochannels on the water and ion transport.It was found that there was an ionic Coulombic blocking effect in the longer graphene nanochannels,and the existence of this effect could effectively inhibit the transport of water molecules.The results also showed that the ionic Coulombic blocking effect could be controlled by changing the applied electric field intensities,and as a result,the transport of water molecules in the graphene nanochannels could also be controlled.