Research On Effects Of Modification On Transport Properties Of Fluids In Silica Gel Nano-Channel

Micro/Nano electro mechanical system is an important part of micro/nano technology,properties and behaviors of material in micro/nano electro mechanical systems bring about some nonignorable changes compared with that at the micro-or macroscale.Silica gel particles have nanoscale transmission channels between the cavity and the particle surface,chemical composition of the channel wall with the modification have change inherently,the "surface effect" of nano-channel with the modification has a significant impact on the transport behaviors and properties of fluid water.Therefore,the research on the influence of transport properties of fluids in silical gel nano-channel with modification has a certain guiding significance for its modifying and its application in micro-nano electromechanical system.In this paper,nanometer flow model has been established based on the molecular dynamics method,and speed,density and dipole orientation distribution of liquid water in the silica gel nanochannel have been studied in detail.We investigate the formation of hydrogen bonds between water and the wall,and diffusion behavior and viscosity properties of flowing water in the nano-channel have been further studied.First of all,that modification impacts on wettability of silica nano-channel has been explored.The speed,density and dipole orientation distribution of liquid water in the silica gel nanochannel have been simulated and calculated,we found that the nano-channel wall with hydroxylation shows strong hydrophilicity,and the nano-channel wall with silanization shows strong hydrophobicity,slip length of fluid and the alkyl chain length of modification layer have a little linear relationship;dipole orientation of fluid water in hydroxylation nano-channel is more orderly,and it has strong hydrogen bonding with water molecules.Dipole orientation of fluid water in nano-channel wall with silanization is disorder relatively,and and it hasn’t hydrogen bonding with water molecules.Second,that modification impacts on diffusion behavior of fluid water in silical nano-channel has been explored.The mean square displacementand and the diffusion coefficient of liquid water in the silica gel nanochannel have been simulated and calculated,we found that diffusion coefficient of liquid water in the hydroxylation nano-channel is far less than it in the silanization nano-channel,but they all should be less than the diffusion coefficient of bulk water,the "surface effect" of nano-channel of the silical with modifiction transmission play dominant roles as the fluid water transfer in nano-channel.Local diffusion coefficient of water in nano-channel has been further investigated,we found that local diffusion coefficient of water fluid in nano-channel is related to its distance to the wall.Finally,that modification impacts on viscosity properties of fluid water in silical nano-channel has been studied.Viscosity properties of liquid water in the silica gel nanochannel have been simulated and calculated,we found that viscosity of liquid water in the hydroxylation nano-channel,viscosity of liquid water in the hydroxylation nano-channel is 11 times as large as the viscosity of bulk water;Viscosity of liquid water in the silanization nano-channel after modifiction is 1/5 times as large as the viscosity of water in the hydroxylation nano-channel,and is 2 times as large as the viscosity of bulk water.With the augmentation of the modification degree,the viscosity of liquid water in the silanization nano-channel decreases;The viscosity distribution of liquid water in nano-channel has been further discussed,we found that local viscosity of water fluid in nano-channel is related to its distance to the wall.