Mohammed A. Bahattab

From hydrophobic to hydrophilic polyvinylidenefluoride (PVDF) membranes by gaining new insight into material's properties

This work provides an easy and versatile strategy to manufacture novel polyvinylidenefluoride (PVDF) membranes by solution casting and phase separation techniques displaying tailored physicochemical and microstructural features depending on the opportune combination of functionalization by blending chemical additives (multiwalled carbon nanotubes, MWCNTs) and manufacturing procedure. The systematic study of the effect of (i) polymer concentration, (ii) use of pore forming additives (LiCl), and (iii) type and concentration of MWCNTs, on the PVDF crystalline composition and membrane microstructure, highlights the strong relationships of these parameters with the wettability, fouling and transport attributes of the formed membranes. The results provide the key to discriminate membrane preparation conditions favoring hydrophilic, low fouling, and highly selective PVDF–MWCNTs membranes, for water-treatment applications in pressure-driven membrane operations, from conditions favoring the formation of hydrophobic and waterproof membranes, to be used in the membrane contactors field. Also, they open exciting perspectives for a more effective development of PVDF-based nanostructured membranes for advanced separations based on a comprehensive investigation and understanding of materials properties.

Comparative Properties of Hydrophilic and Hydrophobic Fumed Silica Filled Two-Component Polyurethane Adhesives

Two fumed silicas, one hydrophilic and another hydrophobic, were added to a two-component polyurethane (PU) adhesive and their properties compared. The filled polyurethanes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and water and diiodomethane contact angle measurements. The adhesive strength was evaluated from single lap-shear tests of solvent wiped stainless steel/polyurethane adhesive joints. The fumed silicas were well-dispersed in the polyurethane matrix as bundles of nanometric spherical silica particles. However, some micron size agglomerates of fumed silica appeared in the filled polyurethane. The addition of fumed silica favoured the degree of phase separation between the hard and the soft segments in the polyurethane. The polyurethanes were not fully cured under the conditions used in this study and the addition of fumed silica inhibited the curing reaction; the extent of the curing reaction was not a...Two fumed silicas, one hydrophilic and another hydrophobic, were added to a two-component polyurethane (PU) adhesive and their properties compared. The filled polyurethanes were characterized by thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and water and diiodomethane contact angle measurements. The adhesive strength was evaluated from single lap-shear tests of solvent wiped stainless steel/polyurethane adhesive joints. The fumed silicas were well-dispersed in the polyurethane matrix as bundles of nanometric spherical silica particles. However, some micron size agglomerates of fumed silica appeared in the filled polyurethane. The addition of fumed silica favoured the degree of phase separation between the hard and the soft segments in the polyurethane. The polyurethanes were not fully cured under the conditions used in this study and the addition of fumed silica inhibited the curing reaction; the extent of the curing reaction was not affected by the hydrophilic or hydrophobic nature of the fumed silica. The filled polyurethanes were further cured during DSC experiments and this was noticed by the appearance of the melting of the hard segments and the displacement of the second glass transition to a higher temperature. On the other hand, the addition of fumed silica increased the wettability and the surface energy of the polyurethane; this increase was mainly due to an increase in the polar component of the surface energy. The increase in surface energy is somewhat more marked in the case of the hydrophilic silica filled polyurethane, indicating that the polarity of the fumed silica affected the surface properties of the polyurethane. Finally, the addition of the hydrophilic fumed silica increased the adhesion of the filled polyurethane adhesive to stainless steel which was in agreement with the higher surface energy of the hydrophilic fumed silica filled polyurethane.

Polyvinylidenefluoride/carbon nanotubes mixed matrix membranes with tailored properties

Membrane operations are promising tools for efficient and environmentally friendly separations. However, the development of advanced membranes with tailored properties is a key issue to be addressed in order to better exploit the potentialities of membrane-based separations. An important approach toward this aim is the development of mixed matrix membranes in which an organic and an inorganic phase coexist in order to have synergic effects on membrane properties. The peculiar properties of carbon nanotubes (CNTs) such as high electrical and thermal conductivity, high strength and unique transport properties, has motivated a considerable effort to produce CNT-polymer composites in order to engineer membrane properties. In this work the roughness, wettability, morphology, crystalline phase and pore size of polyvinylidenefluoride (PVDF) membranes were tailored working on the membrane preparation conditions, as well as, by blending the polymer with multiwalled carbon nanotubes (MWCNTs). A study on the effect ...