PVDF Composite Membrane Research Articles

Enhancement of Cycle Performance of Lithium Secondary Batteries Based on Nano-Composite Coated PVdF Membrane

The multilayered membrane for lithium rechargeable batteries based on poly (vinylidene fluoride) (PVdF) is prepared with the coated layer containing nano-sized filler. The prepared membranes were subjected to studies of mechanical strength, morphology, interfacial stability, impedance spectroscopy, ionic conductivity, and cycle performance. The localized inorganic filler in the PVdF composite membrane rendered mechanical strength much reduced because of its low stretching ratio and it results in around half value of the mechanical strength of highly stretched PVdF membrane. In order to achieve high ionic conductivity and interfacial stability without sacrificing high mechanical strength, coating layer with nano-filler was newly introduced to PVdF membrane. The ionic conductivity of the coated membrane was 1.03 mS/cm, and the interface between the coating layer and PVdF membrane was stable when the membrane was immersed into liquid electrolyte. The discharge capacity of the cell based on nano-filler coated PVdF membrane was around 91% of the initial discharge capacity after 250 cycles, which is an improvement in cycle performance compared to the case for the non-coated PVdF membrane.

Pervaporation performance analysis and prediction—using a hybrid solution-diffusion and pore-flow model

A hybrid mathematic model for pervaporation is proposed which incorporates the concepts of solution-diffusion model and pore model. The model allows performance prediction as well as the establishment of the internal concentration and pressure profiles within the membrane. The model parameters specific to the particular membrane and mixture system are determined using liquid sorption and pervaporation experimental data. The model is experimentally examined using ethanol–water mixtures and poly(dimethyl siloxane)–poly(vinyldiene fluoride) (PDMS–PVDF) composite membranes. The characteristics of flux and separation factor predicted using the model are in fair agreement with the experimental data under various feed concentrations and downstream pressures for different membrane arrangements, including single-layer, reverse single-layer and double-layer PDMS–PVDF composite membranes. Internal profiles of pressure, concentration and component mole fraction can be established using the model. Concentration polarization phenomena for ethanol and water are located at membrane interfaces and vapor–liquid interfaces, respectively. Performances of several different membrane designs are compared using the model.

Effect of TiO2 nanoparticle size on the performance of PVDF membrane

The comparison of the performance and morphology was carried out between neat PVDF membrane and PVDF composite membranes with nanosized TiO2 particles of different size. The results of permeability and instrumental analysis illustrated that nanometer size obviously affected the performance and structure of the PVDF membranes. The smaller nanoparticles could improve the antifouling property of the PVDF membrane more remarkably. The surface and cross-section of the membranes were observed with an atomic force microscopy (AFM), a scanning electron microscope (SEM). The TiO2/PVDF membrane with smaller nanoparticles had smaller mean pore size on its surface and more apertures inside the membrane. X-ray diffraction (XRD) experiments also suggested that smaller TiO2 nanoparticles had stronger effect on the crystallization of PVDF molecules.

Modified silicone–PVDF composite hollow‐fiber membrane preparation and its application in VOC separation

AbstractPolydimethylsiloxanevi–poly(vinylidene fluoride) (PDMSvi–PVDF) composite membranes were prepared using asymmetric PVDF hollow‐fiber membranes as the substrate where a very thin layer of silicone‐based coating material was deposited via a developed dip coating method. The preparation of the composite membranes under various conditions were investigated. In the optimal coating procedure, homogenous and stable oligo‐PDMSvi coating layers as thin as 1–2 μm were successfully deposited on the surface of PVDF membranes. The developed PDMSvi–PVDF composite membranes were applied for separation of a wide variety of volatile organic compounds (benzene, chloroform, acetone, ethyl acetate, and toluene). The results showed that the PDMSvi–PVDF hollow‐fiber composite membranes that had been developed exhibited very high removal efficiency (>96%) for all the VOCs examined under favorable operating conditions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Preparation of poly(vinylidene fluoride)(pvdf) ultrafiltration membrane modified by nano-sized alumina (Al 2O 3) and its antifouling research

Organic–inorganic composite membranes are formed by nano-sized alumina particles uniformly dispersed in the poly(vinylidene fluoride) solution (19% polymer weight). Membranes were prepared by phase inversion process and were characterized by ultrafiltration (UF) experiments in terms of water flux, molecular weight cut-off for the wet membranes. Contact angle between water and the membrane surface were measured by contact angle measurement in order to characterize the hydrophilicity changing of the membrane surface. The cross-sectional structures, porous dispersion in membranes surface and nanometer particles distribution in the membrane were examined by scanning electron microscopy (SEM) and transmission microscopy (TEM), respectively. The effect of nanometer Al 2O 3 particles concentration in the polymer dope on the permeation properties, membrane structures and antifouling performances were examined. The experimental results indicate that Al 2O 3–PVDF composite membranes exhibit significant differences in surface and intrinsic properties due to nanometer particles addition.

Concentration of dilute flavor compounds by pervaporation: permeate pressure effect and boundary layer resistance modeling

Pervaporation experiments with flat sheet PDMS–PVDF composite membranes were carried out at ambient temperature (20–22 °C) to concentrate three flavor compounds (ethyl butyrate, benzaldehyde, and trans-2-hexenal) from dilute aqueous solutions. Due to the different thermodynamic properties (saturated vapor pressure and activity coefficient) of these flavor compounds, the effects of downstream permeate pressure on the organic flux and the enrichment factor varied. The results were correlated with simple mass transfer equations. The organic and water fluxes at different feed flow rates were measured. The feed flow rate had negligible effect on the water flux because of the dilute solute concentration in the feed solution. However, for the organic flux, the significant effect of the feed flow rate proved the existence of a mass transfer boundary layer on the membrane feed side. A concentration polarization model derived from a steady state flux equation was used to calculate the liquid boundary layer thickness on the feed side and the organic mass transfer coefficient in the membrane. Using the resistance-in-series model, the mass transfer resistance of the liquid boundary layer was separated from the mass transfer resistance of the membrane. It was clearly shown in this work that the mass transfer resistance of the boundary layer was controlled by hydrodynamic conditions, while the varying degrees of flavor concentration results were mainly due to the different thermodynamic properties.