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The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Young's modulus.

Soluble polyelectrolyte complexes (PECs) between chitosan (CS) and sodium carboxymethyl cellulose (CMCNa) were synthesized in aqueous hydrochloric acid (HCl) and obtained in their solid form. FT-IR, elemental analysis (EA), thermal gravity analysis (TGA), wide-angle X-ray diffraction (WAXD), and viscometry were used to characterize the chemical structure, composition, thermal stability, crystallinity and solution property of PECs, respectively. These PECs could be dissolved in aqueous NaOH and their homogeneous polyelectrolyte complex membranes (HPECMs) were made by solution casting method. Both the surface morphology of HPECMs and the morphology of single PEC aggregate were examined by field emission scanning electron microscope (FESEM), and atomic force microscopy (AFM). Effects of the water content in aqueous ethanol and temperature on the swelling behavior and pervaporation dehydration of HPECM were examined. A good performance of J = 1.14 kg/m2 h, α = 1062 was obtained with HPECM0.25 in dehydrating 10 wt.% water–ethanol at 70 °C. The swelling behavior and pervaporation performance were interpreted in terms of structure characteristics of both PECs and HPECMs.

Polyelectrolyte complexes (PECs) between poly(diallyldimethylammonium chloride) (PDDA) and sodium carboxymethyl cellulose (CMCNa) with four ionic complexation degrees (ICD) were synthesized and their homogeneous polyelectrolyte complex membranes (HPECMs) were fabricated. Elemental analysis and FT-IR were used to determine the composition and chemical structure of PECs. Thermogravimetric analysis (TGA), wide-angle X-ray diffraction (WAXD) and viscometry were used to characterize the thermal stability, crystallinity and solution properties of PECs, respectively. Field emission scanning electron microscope (FESEM) was used to examine the surface morphology of HPECMs, which were subjected to the pervaporation dehydration of isopropanol. Effects of membrane fabrication methods, cycling of feed temperature and ICD of PECs on pervaporation performance of HPECMs are discussed. Meanwhile, HPECMs were also subjected to dehydration of three other organics and showed very good performance. All these performances are explained in terms of the unique structural characteristics of PECs and HPECMs.

Polyethylenimine/poly(acrylic acid sodium salt) (PEI/PAA) ultrathin polyelectrolyte multilayer membranes were fabricated by an electric field enhanced method and were used for isopropanol/water pervaporation. Surface properties of the electric field enhanced multilayer polyelectrolyte membranes (EPEMs) prepared under different conditions were investigated by atomic force microscopy (AFM) and contact angle (CA) measurements. It was found that surface properties (roughness and hydrophilicity) of EPEMs strongly depend on the direction of the electric field, dipping time, applied voltage, number of bilayers, which, in turn, affect their pervaporation performance. The (PEI/PAA)4PEI EPEMs fabricated with a dipping time of 15 min and an applied voltage of 5 V for separating 10 wt% water–isopropanol mixtures exhibited high separation factor and large flux. Meanwhile, the performance of the EPEMs displays good storage stability within 60 days.