Study On Mass Transport Properties In Array Nanochannels

The transport of mass and charge in nanoconfined spaces with at least one dimension smaller than 100 nm occurs in a unique way which is not observed in the bulk.For example,the flow of water inside hydrophobic carbon nanotubes is 104?105 faster than in the bulk.Ion mobility in nanoconfined spaces is also much higher than the bulk.The mass transportation in nanochannels shows a remarkable selectivity.Due to these special transport properties,nanochannels have been applied in many fields such as DNA sequencing,single molecule detection,bionic sensor design,drug delivery,biochemicals separation and analysis.It is clear that understanding of the transportation of ions and molecules in nanochannels will extend the application fields of nanochannels.Porous anodic alumina(PAA)membranes have been widely used in many areas due to the uniformed parallel nanochannels with high density.The preparation method of PAA is relatively mature.The size of nanochannels and the distances between nanochannels can be regulated through different oxidation voltage and natures of electrolyte solutions.In addition,the surface charge of PAA membranes can be altered simply by changing the pH value of the electrolyte solutions due to the amphoteric properties of alumina.This thesis will focus on the fabrication of nanochannels,exploration of the fundamentals of nanochannels such as interaction between ions and nanochannels,ions transport properties in nanochannels.Detailed description is as follows:1.Ionic current rectification properties of alumina nanochannel arrays prepared through an accurate positioning and layer-by-layer modification techniqueA new ionic current rectification(ICR)device responsive to a broad range of pH stimuli is established using highly ordered nanochannels of PAA membrane with abrupt surface charge discontinuity.The asymmetric surface charge distribution is achieved by patterning the nanochannels with surface amine functional groups at designed positions using a two-step anodization process.Due to the asymmetric potential distribution caused by abrupt surface charge discontinuity,the nanochannel array based device is able to regulate ion transport selectivity and has ionic current rectification properties.The results indicate that,pH of the electrolyte solution has an important effect on the polarity of ICR and the rectification ratio.In addition,the size of the nanochannel has a direct influence on the rectification ratio.The rectification ratio of 20 nm nanochannel is lager than that of 40 nm nanochannel under the same conditions.Numerical simulations show that ICR is caused by ions accumulation and depletion in nanochannels due to asymmetric charge distribution.2.Ionic current rectification properties of branched nanochannel arrayAn novel conception is proposed to construct an ICR device responsive to a broad range of pH stimuli using highly ordered PAA membrane with tailor-made branching nanochannels array.The relationship between the pH value of solution and rectification properties was studied.In addition,a 3D model was built to explore solution concentration and potential distribution in branching nanochannels.In experiments,branched PAA membrane was prepared using two-step reducing anodizing approach.A novel ionic current rectification device was then constructed based on the branched structure to achieve the rapid and sensitive response to solution pH.The rectification ratio and polarity of rectification could be altered by changing solution pH and size of the nanochannels.The 3D model simulations indicate that,ICR and ions selective transportation are caused by the asymmetric distribution of energy and electric potential in nanochannels due to the geometry abruptly changing.Compared to 2D model,3D model has advantages in describing the changes in electric potential and ion concentration at the interface of the geometry with abrupt change.3.The ionic rectification characteristics of ion channel-nanochannel hybridThe PAA membranes constituting of porous layer and barrier layer were prepared by anodic oxidation.The structure of the barrier layer was studied for the first time.The results show that there is a mass of small sized ion nanochannel(0.7-1.3 nm).A novel ionic rectification device was constructed by combining the porous layer and barrier layer.Transport of ions with different valence and concentration in ion channel-nanochannel hybrid was studied in detail.The ionic rectification phenomenon appears due to the potential asymmetrical distribution caused by geometry abrupt changing when nanochannels convert to ion nanochannel.The ionic rectification characteristics are determined by solution pH in monovalence ionic solution,but it can be regulated by ion concentration in multivalent ion solution,besides solution pH.A new method was proposed to built ionic rectification device,which extends the application fields of the PAA membranes.4.Regulation properties of array nanopores electrodeA novel Au nanopore array electrode with pH or light controlled mass transport was fabricated via alternating electrochemical deposition.The regulated properties were measured by the steady-state limiting current of electrochemical active probe Fe(CN)63-.The results show that,flux of the active probe in nanochannels can be regulated by varied solution pH when the nanochannel size becomes comparable to the thickness of electric double layer(EDL)in low concentration electrolyte solutions.For light controlled system,the surface of nanochannels was modified with a photo-chromic spiropyran and the flux of active probe in nanochannels can be regulated by light illumination with different wavelengths.The research for ions asymmetrical transport in the nanochannel is useful for further understanding the mass transport in nanospace.It is clear that understanding of the mass transport properties helps in designing and preparing functional nanochannels and corresponding smart devices.In addition,the present work would provide fundamentals for understanding the function of complicated biological ion nanochannels.