【作者】 张鹏；

【导师】 钱锦文；

【作者基本信息】 浙江大学 ， 高分子化学与物理， 2008， 博士

【摘要】 通过层层自组装（layer-by-layer self-assembly,LbL SA）技术,将带相反电荷的两种聚电解质组装在基片上,形成厚度和组成比较均一的聚电解质多层复合膜（Polyelectrolyte multilayer membrane,PEM）是近年来许多领域研究的热点之一。本文从聚电解质种类及其溶液性质出发,重点研究聚电解质自组装过程中各种内外因素对溶液性质和自组装膜的表面性质、吸附量及其异丙醇脱水的分离性能影响,进而完善和深化层层自组装的机理。选用两种水溶性的强电解质聚（二甲基二烯丙基氯化铵）（PDDA）和聚苯乙烯磺酸钠（PSS）为研究对象,通过改变电解质溶液中离子强度、pH、溶剂性质及组装温度,用乌氏粘度计测定聚电解质在各组装溶液中的特性粘数及用紫外-可见光谱仪（UV）和石英微晶天平（QCM）测定由各种组装溶液所得PDDA/PSS多层膜聚电解质吸附量。实验结果发现,聚电解质在各种组装液中的特性粘数（链尺寸）和组装膜的吸附量基本上呈现反比关系。原子力显微镜（AFM）结果显示,当溶液中的聚电解质链尺寸减小时所得组装膜的表面更为粗糙,也呈现聚电解质在溶液中的特性粘数与其组装膜的表面粗糙度呈负相关的现象。选用水溶性的强电解质PDDA和非水溶性的不同磺化度和分子量的磺化聚砜（SPSF）为研究对象,以N,N-二甲基甲酰胺（DMF）及N,N-二甲基甲酰胺-水（DMF-H₂O）混合溶剂为SPSF的溶剂,分别用乌氏粘度计和电导率仪测定了SPSF在不同组成的DMF-H₂O混合溶剂中的特性粘数及不同磺化度SPSF在各DMF-H₂O混合溶剂中的电导率。实验结果显示,由水溶性的强电解质PDDA与非水溶性不同磺化度SPSF所得组装膜的厚度强烈依赖于SPSF的电荷密度（磺化度）及组装混合溶剂中DMF的体积分数(φ_DMF)。当_DMF为0.8和0.9时,两种PDDA/SPSF多层膜,PDDA/SPSF65和PDDA/SPSF85,厚度都呈极大值,而当φ_DMF约为0.6～0.7时,两种PDDA/SPSF多层膜的厚度都呈极小值;在相同组装层数下,电荷密度较小的PDDA/SPSF65膜的厚度比电荷密度较大的PDDA/SPSF85多层膜的厚度更大;多层膜的厚度随组装层数增加呈线性增长;另外,PDDA/SPSF多层膜的接触角及表面粗糙度也随厚度的增加而上升。实验结果证明PDDA/SPSF多层膜的性质受到SPSF在不同φ_DMF中的线团尺寸及电离度影响。同时DMF-H₂O混合溶剂的性质强烈地影响SPSF溶液的性质,从而进一步影响了在不同φ_DMF下PDDA/SPSF多层膜的性质。以带负电的聚酰胺反渗透膜为底膜,在不同NaCl离子强度下制备了PDDA/PSS聚电解质多层膜。扫描电镜（SEM）测试结果表明,随组装溶液中NaCl浓度增大单层膜厚度增加,膜表面变得平坦光滑。渗透汽化结果表明,增加盐的浓度能大大提高组装膜的分离选择性。在35℃的操作温度下（PDDA/PSS）₆PDDA多层膜用于分离含水5 wt%的异丙醇-水混合溶液,组装液中NaCl浓度为0.1 M和1 M时,膜的通量分别为2.57 kg.m^-2.h^-1和1.67 kg.m^-2.h^-1,而分离因子则从46上升到246。随着组装层数的增加,组装膜的表面变得光滑,分离因子升高而通量下降。在盐浓度较高情况下提高外加盐浓度比增加组装层数对提高膜的分离因子更有效。操作温度和料液组成对PDDA/PSS聚电解质多层膜的分离性能有很大影响。随着组装溶液中水含量的增多,PDDA/PSS聚电解质多层膜的通量迅速上升,透过液的水含量略有下降。PDDA/PSS聚电解质多层膜分离含水5 wt%的异丙醇-水混合液时,发现组装膜的通量和分离因子随着操作温度的上升同步上升,呈反“trade-off”现象。在分离水含量较高混合液（水含量20～30 wt%）时由于聚电解质膜溶胀性增加,反“trade-off”现象消失。在电场下制备了三种聚电解质层层自组装膜,PDDA/PSS,PDDA/PAA和PEI/PAA电场促进自组装膜（EPEM）。考察了组装条件对各种自组装膜的表面形貌及其渗透汽化性能的影响。实验结果证明,沿着电场力方向组装的PEI单层膜表面粗糙度增大,渗透汽化分离性能有明显提高,这表明电场加快组装速度和增大聚电解质吸附量,从而提高了膜的选择性。由PEI单层膜组装的表面粗糙度及渗透汽化实验确立了最佳组装时间为15 min,最佳组装电压为5 V。PDDA/PSS,PDDA/PAA和PEI/PAA三种膜优先透水的选择性依次递增;电场促进自组装多层膜（EPEM）的表面粗糙度比相同组装条件下普通自组装多层膜（PEM）粗糙度低,用于分离异丙醇-水混合溶液时有很高的分离性能。渗透汽化分离实验显示,几个双层的PEI/PAA EPEM用于分离异丙醇-水混合溶液时,在较大操作温度（40～70℃）及料液浓度范围内（水含量5～30 wt%）都具选择性高,渗透通量大、重复性好以及高稳定性的特点。例如（PEI/PAA）₄PEI EPEM,在渗透汽化操作温度为70℃用于分离含水10 wt%的异丙醇-水体系时,其通量高达4.05 kg.m^-2·h^-1,分离因子为1075;在70℃分离分离含水30 wt%的异丙醇-水体系时,其通量高达7.65 kg.m^-2.h^-1,透过液水含量仍保持94.38 wt%。更多还原

【Abstract】 In the past decade,the layer-by-layer（LbL）self-assembly of polyelectrolytes（PE） has been considered to be the simplest and most convenient way for fabricating thin multilayer membranes with a well-defined thickness and chemical composition. However,due to its short developing history,many things are still uncertain for this novel technology which limits its application in many aspects.In order to further discover the rule of PEM during the LbL process,a series of protocols were established to investigate the properties of PEMs.Solution properties of PEs and properties of multilayer membranes were investigated to discover the relation between the surface properties,membrane thickness and separation performance.Self-assembly layer-by-layer multilayer membranes of two typical PEs,poly （dimethyl diallylammonium chloride）（PDDA）and poly（styrenesulfonate sodium salt） （PSS）were fabricated from dipping solutions with different added salt concentrations, pH,solvent compositions and temperature respectively.The absorption amount of PDDA/PSS self-assembled multilayer membranes in designed dipping solvents was measured by UV-vis-spectroscopy（UV）and quartz crystal microbalance（QCM）. Intrinsic viscosities of PDDA and PSS in corresponding dipping solvents were determined by an Ubbloheode viscometer.The adsorption amount of PDDA/PSS multilayer membranes increases with decreasing the intrinsic viscosity of PDDA or PSS in different corresponding dipping solvents.That is,a negative relation between the adsorption amount of PDDA/PSS multilayer membranes and the chain dimension of PDDA and PSS in the dipping solvents exhibits for all assembly systems of PDDA and PSS except for that of PSS in the media with pH_PSS＞10.The negative relation is trusty in spite of the designed dipping solvent for only PDDA or PSS and for both of them.The high adsorption amount of PDDA/PSS multilayer membranes could be attributed to low excluded volume of the compact chain with low intrinsic viscosity of the polyelectrolyte in the dipping solvent.The AFM images show that polyelectrolyte with compact chains in solutions would form thick membranes with rough surfaces. Two sulfonated poly（sulphone）sodium salts（SPSFs）with different molecular weights and ionic exchange capacities in a N,N-dimethyl formamide/water（DMF-H₂O） mixed solvent with various DMF contents(φ_DMF)were selected as a model system for investigating the influences of solvent composition,solution properties,and charge density of polyelectrolytes on the layer-by-layer（LbL）self-assembly of water-insoluble polyelectrolytes.PDDA in aqueous solution was used as the counterpart.Intrinsic viscosity and conductivity of SPSF(ηSPSF and L_SPSF)in solutions with differentφ_DMFwere investigated.The PDDA/SPSF multilayer membranes grew nearly linearly with the layer numbers regardless of theφ_DMFin the SPSF solutions. The total absorption amount of the PDDA/SPSF multilayer membranes was strongly dependent on the charge density of the SPSF molecules and theφ_DMFvalue of the SPSF solutions.Minimum values and maximum values of absorption amount were observed atφ_DMF0.6～0.7 andφ_DMF0.8～0.9 respectively.On the other hand,the SPSF with a lower ionic exchange capacity led to thicker multilayer membranes for any givenφ_DMFvalue in the SPSF solutions.The average thickness of each bilayer was about 3.5～7.5 nm for PDDA/SPSF85 or 5.6～13.3 nm for PDDA/SPSF65,depending on the solvent composition.Surface roughness and contact angle of PDDA/SPSF increase with increasing membrane thickness.The results indicate that the molecular structures of the DMF-H₂O mixed solvent strongly affect the solution properties of SPSF,which in turn determine the growth behavior and physical properties of the PDDA/SPSF multilayer membranes.PDDA and PSS in solutions with different NaCl concentrations were self-assembled onto a polyamide reverse osmosis membrane and used for dehydration water from isopropanol.The influences of NaCl concentration of the dipping solutions, number of the bilayers and feed temperature on the pervaporation performance of PDDA/PSS multilayer membranes were investigated.Scanning electron microscope （SEM）experiment showed that the membrane surface becomes smoother with increasing NaCl concentration in dipping solutions.The results of the pervaporation tests showed that the PDDA/PSS membranes assembled in high NaCl concentration have good pervaporation performance.The separation factor is 345 and permeate flux is 2.51 kg.m^-2.h^-1for（PDDA/PSS）₆PDDA multilayer membrane assembled in 1 M NaCl used for pervaporation of 95 wt%isopropanol isopropanol-water mixtures at 35℃.With increasing operation temperature,both the flux and separation factor increase.However,the separation factor decreases with increasing operation temperature when increases the water percent in feed.An anti-"trade-off" phenomenon is found in low water percent in feed and explained in term of both solvent interaction and structure of LbL membrane.An electric field enhanced method is developed for fabricating layer-by-layer （LbL）self-assembly polyelectrolyte multilayer membranes.Three kinds of electric field enhanced polyelectrolyte multilayer membranes（EPEMs）,poly（diallyl dimethylammonium chloride）/poly（styrenesulfonate sodium salt）（PDDA/PSS）,poly （diallyldimethylammonium chloride）/poly（acrylic acid sodium salt）（PDDA/PAA） and polyethylenimine/poly（acrylic acid sodium salt）（PEI/PAA）,were self-assembled on a polyamide reverse osmosis membrane.The pervaporation performances of EPEMs for separating isopropranol-water mixtures（90/10,w/w）are all superior to those of corresponding normal self-assembled polyelectrolytes membranes（PEMs）, and the selectivity increases with PDDA/PSS,PDDA/PAA and PEI/PAA in order. The surface properties and pervaporation performance of PEI/PAA EPEM fabricated in different conditions were investigated.The results show that the electric field can improve the self-assembly process.The best dipping time of each layer is 15 min and the best applied voltage is 5 V.The PEI/PAA EPEM shows high performance and good selectivity in a large-scale temperature（40～70℃）and water feed concentration （water in feed:5～30 wt%）.For（PEI/PAA）₄PEI EPEM,the separation factor is 1075 and permeation flux is 4.05 kg.m^-2·h^-1for separating isopropranol-water mixtures（90/10,w/w）at 70℃.更多还原