Study Of Flow-induced Translocation Of Flexible Polymer Linear Chains Through Nanochannels In Dilute Solutions

This Ph.D.thesis focuses on the flow-induced translocation behavior of flexible linear chains passing through nanochannels in dilute solutions.We illustrated the core regime of confined conformation transition for linear chains,clarified the lasting debate of chain length dependence,revealed the significant influence of solution concentration and pore structure on translocation behavior,and further explored the application of flow-induced translocation method in polymer separation and fractionation.Based on the research and understanding of chain length dependence of confined conformation transition,we expanded the study on the regulatory regime of chain length effect on chain conformation and catalytic mechanism in typical catalytic systems.The main results are as follows:1.Illustrating the core regimes of flow-induced translocation of flexible linear chains through nanochannels.Using mono-and polydisperse polystyrenes model samples,we investigated the conformation transition behavior of linear chains passing through 20 nm nanochannels in the whole length range(1.0<R/r<9.5,where R and r represent the chain size and the pore size,respectively),and clarified the influence of the chain length of flexible linear chains on their confined conformation transition behavior.We,for the first time,revealed that there exist two different translocation regimes,i.e.,strong and weak confinement regimes.In the strong confinement regime(R/r>λ*,where)λ*represents the critical relative chain length),the critical flow rate(qc)is found to be independent of the chain length,consistent with the prediction by classical theories,while in the weak confinement regime(R/r<λ*),qc increases with the chain length significantly.Furthermore,by considering the variation of both position(L)and height(Ebar)of the energy barrier in the weak confinement regime,a normalization equation has been proposed to correlate the normalized critical flow rate(qc/qc*)with the normalized confined length(L/l*)and energy barrier(Ebar/Eba*),i.e.,qc/qc*=(2L/l*-Ebar/Ebar*)/(L/l*)2,where qc*,l*and Ebar*are corresponding physical quantities in the strong confinement regime.The theoretical equation describes our experimental data well.2.Revealing "the interaction among flow fields between channels" and "chain pre-confinement effect" in the flow-induced translocation of linear chains through nanochannels.Confined conformation transition behavior in the flow-induced translocation of polymer chains passing through nanochannels is closely related to the transition width and the critical flow rate(qc).Using a special anisotropic membrane with bilayered cylindrical channels,we reveal the significant effects of "the interaction among flow fields between channels" and "chain pre-confinement effect" on qc and the transition widths.The results show that the interaction between the flow fields at different pore entrances will lead to an increase of about one order of magnitude in the apparent qc value,which is due to the fact that the long linear chain can be in different tensile flow fields at the same time,leading to the dissipation of hydrodynamics force.In addition,we also found that the pre-confinement of the polymer chain in the macropore can reduce the conformation entropy penalty when it translocated through the nanochannels,resulting in the reduction of the apparent qc value and the transition width.This work is of great significance for the ideal modeling and practical application of the flow-induced confined conformation transition.3.Developed the standard method to separate linear,comb-like and hyperbranched polymers by flow-induced translocation progress and constructing the prototype apparatus.At the technical level,flow-induced translocation progress is closely related to the ultrafiltration technology.Based on the study and understanding of the confined conformation transition regime for polymer chains,we further explored the feasibility of utilizing the "Dead-end" ultrafiltration technology for polymer separation/fractionation/characterization from both theoretical and experimental perspectives.Theoretically,advantages/disadvantages of "Dead-end" ultrafiltration and some other popular polymer separation/fractionation techniques(PSFTs)were compared and discussed;Experimentally,a home-designed ultrafiltration prototype apparatus was developed and successfully applied to execute various separation/fractionation tasks for mixed solutions of polymer chains with varied topologies or/and varied sizes at laboratory scale.Based on theoretical modeling and experimental examination,the ultrafiltration system containing a detection module that can complement the prevailing PSFTs is found to be a powerful PSFT with the merits of low cost,high efficiency,high accessibility,easy handling,and universal applicability.4.Revealing the regulation regime of chain length effect on chain conformation and catalytic mechanism in the catalytic system of water oxidation.Based on the research and understanding of chain length dependence of confined conformation transition,we expanded the study to the application of chain length effect in catalytic systems.We prepared four P4VP-RuⅡ(bda)polyelectrolyte-metal complexes with different chain lengths and controlled Ru loading amounts as catalysts for catalytic water oxidation.Combining the experimental results of catalysis kinetics and kinetic isotope effect,we found that the catalytic mechanisms of four kinds of P4VP-Ru are independent of chain length,which means all of them are single-site water nucleophilic attack(WNA),rather than the interaction between two metal oxide units(I2M)as predicted from literature.Furthermore,combining with dynamic light scattering characterization,zeta-potential measurement and molecular dynamics simulation,we demonstrated that the slow diffusion and multi-charge properties of polyelectrolyte ligands can be balanced against the chain length dependent flexible effect,which is the root of the transition of mechanism from WNA to I2M.