| Nanofluidics is the reseach of mass transport in nanochannels, of which at least one dimention is smaller than 100 nm. It differs greatly from that at the bulk-scale, since various interfacial forces, including steric interactions, van der Waals forces and electrostatic forces, become important due to the large surface-to-volume ratios. For example, electrical double layer overlapping would occur in the nanochannles becaused of the equivalent size of the channel to that of the thickness of electrical double layer of the channel walls, which results in unusual mass transport phonomenon, such as selective ion transport, ion enrichment and depletion and ionic rectification. A nanoscale understanding of mass transport is crucial to gaining fundamental insights into the molecular intera ction and mass transport control in the nanoconfined space, and improving the design of nanofluidic devices for molecular detection and separation. In recent years, the advancement in the fabrication and processing of nanochannels has promoted the experimental nanofluidic reseach. In this thesis, aiming at the understanding of mass transport in the nanochannels and its application in separation and detection, a series of polymer modified nanochannels were prepared via layer-by-layer self-assembly in track-etched polycarbonate membranes(PCTE) and the transport of different charged molecules under different solution conditions was investigated. The research work of this dissertation is summarized as follows:1. Negatively and positively charged nanochannel me mbrane were fabricated via layer-by-layer assembly of different charged polyelectrolyte in PCTE and the transport of water under different eletrolyte gradients was investigated. It was found that the flow direction of water was anomalous under certain eletrolyte gradients, namely, water flowed through the nanochannel membrane from the eletrolyte solution side to the pure water side. In order to clarify the anomalous water transport phenomenon, a water transport model was put forward. According to the model, the anomalous water transport was due to the synergistic effect of concentration diffusion and the induced electroosmosis, which resulted from the diffusion velocity difference of cation and anion under concentration gradients. Via changing the nanochannel surface charge, electrolyte concentration and electrolyte type, the water flow direction could be modulated. In addition, neutral molecule transport, and ionic species separation through charged nanochannel membranes can also be modulated by establishing the electrlyte gradient. This work would contribute to our understanding of water transport property in nanoporous membrane and provide a new route for controlling mass tranport in nanofluidic devices.2. Based on the previous work, a novel method for mod ulating the selective ionic transport in positively charged nanochannles was developed based on the induced electrical field through the nanochanel membrane, which can be adjuted by the phosphoric acid gradient between different sides of the nanochannel me mbrane. The ionic transport through the nanochanel membrane was determined by the synergetic effect of diffusion, induced electroosmosis, and induced electrophoresis. Thus, the ionic transport flux and selectivity can be tuned via changing the phosphoric a cid gradient, permeation time and feed solution volume. The selective transport modulation of methylviologen(MV2+) and 1,5-naphthalene disulfonate(NDS2-) was achieved and the selective factor(CMV2+/CNDS2-) reached 19.5 under optimized condition. The novel method for modulating the selective ionic transport is energy-saving, economic and easy to operate, for it does not require stimulus responsive materials functionalization in the nanochannels and external electrical field. This work would deepen our understanding of ionic transport in nanochannel membrane and provide a new route for ionic transport and separation in nanofluidic devices.3. A p H resonsive nanochannel was constructed based on poly allylamine hydrochloride(PAH) modified nanochannel membrane and it was deveploed as a new method for detection of boric acid via combining the well-known mannitol-boric acid enhanced effect. In the amine groups decorated nanochannels, the transport of NDS2-showed obvious p H responsive property. At centain concen tration of mannitol, NDS2-transport rate in the nanochannels increased as the concentration of boric acid increased, and a novel method for boric acid detection based on NDS2- transport change was developed with a detection limit of 0.07 m M. Compared with the titration method, the nanochannel based aproach consumes low reagent and is eazy to operate. This work provides a new route for detection of substances by changing the microenvironment in the nanochannel via interaction between substanecs.4. Borate and cis-hydroxy compounds gated cascade recognition system was developed in PVA(polyvinyl alcohol) modified nanochannels, which exhibited IMP logic perfromance. The transport of NDS2- in the PVA modified nanochannels decreased obviously in the presence of borate as its binding with PVA turned the channel more negatively charged, and the modulation can be turned back as the binding is reversible. After the negatively charged PVA-borate complex formed in the nanochannels, the added cis-hydroxy compounds formed more stable complex with borate and draged the boracic ion out, which decreased the negative charge in the nanochannel and turn on the transport of NDS2-. Among the common cis-hydroxy compounds, mannitol and sorbitol showed the most obvious gating perfor mance. The recognition system will contribute to the construction of novel nano sensing devices and the biomimics of the biological role of b orate. |
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