Low-surface energy surfactants with branched hydrocarbon architectures

International audienceSurface tensiometry and small-angle neutron scattering have been used to characterize a new class of low-surface energy surfactants (LSESs), "hedgehog" surfactants. These surfactants are based on highly branched hydrocarbon (HC) chains as replacements for environmentally hazardous fluorocarbon surfactants and polymers. Tensiometric analyses indicate that a subtle structural modification in the tails and headgroup results in significant effects on limiting surface tensions γcmc at the critical micelle concentration: a higher level of branching and an increased counterion size promote an effective reduction of surface tension to low values for HC surfactants (γcmc 24 mN m-1). These LSESs present a new class of potentially very important materials, which form lamellar aggregates in aqueous solutions independent of dilution

Effect of Acidic and Basic Conditions on the Plasmon Band of Colloidal Silver

Preparation of colloidal silver nanoparticles has been carried out by salt reduction method and confirmed by the appearance of plasmon band in the visible region. The prepared nanoparticles were subjected to acidic and basic environments. The plasmon band was studied as a function of time under the described conditions and hence used as a stability check of silver nanoparticles in different media. The mechanism of plasmon band disappearance of silver colloids was found to depend strongly on the pH of the medium. Graphical abstract Research highlights ► Plasmon band of silver nanoparticles formed by citrate reduction method is strongly affected by the acidic and basic environments demonstrating effect of pH on the structure and stability of citrate caped silver nanoparticles. ► In acidic condition, an accelerated particle growth results only limited by the buffer action of citrate in solution. ► In the case of base Ag+ ions formation take place which ultimately deposit on the walls of test tube forming a silver mirror

Hybrid Carbon Silica Nanofibers through Sol–Gel Electrospinning

A controlled sol–gel synthesis incorporated with electrospinning is employed to produce polyacrylonitrile–silica (PAN–silica) fibers. Hybrid fibers are obtained with varying amounts of silica precursor (TEOS in DMF catalyzed by HCl) and PAN. Solution viscosity, conductivity, and surface tension are found to relate strongly to the electrospinnability of PAN–silica solutions. TGA and DSC analyses of the hybrids indicate strong intermolecular interactions, possibly between the −OH group of silica and −CN of PAN. Thermal stabilization of the hybrids at 280 °C followed by carbonization at 800 °C transforms fibers to carbon–silica hybrid nanofibers with smooth morphology and diameter ranging from 400 to 700 nm. FTIR analysis of the fibers confirms the presence of silica in the as-spun as well as the carbonized material, where the extent of carbonization is also estimated by confirming the presence of −CC and −CO peaks in the carbonized hybrids. The graphitic character of the carbon–silica fibers is confirmed through Raman studies, and the role of silica in the disorder of the carbon structure is discussed

Hybrid Silica–PVA Nanofibers via Sol–Gel Electrospinning

We report on the synthesis of poly­(vinyl alcohol) (PVA)–silica hybrid nanofibers via sol–gel electrospinning. Silica is synthesized through acid catalysis of a silica precursor (tetraethyl orthosilicate (TEOS) in ethanol–water), and fibers are obtained by electrospinning a mixture of the silica precursor solution and aqueous PVA. A systematic investigation on how the amount of TEOS, the silica–PVA ratio, the aging time of the silica precursor mixture, and the solution rheology influence the fiber morphology is undertaken and reveals a composition window in which defect-free hybrid nanofibers with diameters as small as 150 nm are obtained. When soaked overnight in water, the hybrid fibers remain intact, essentially maintaining their morphology, even though PVA is soluble in water. We believe that mixing of the silica precursor and PVA in solution initiates the participation of the silica precursor in cross-linking of PVA so that its −OH group becomes unavailable for hydrogen bonding with water. FTIR analysis of the hybrids confirms the disappearance of the −OH peak typically shown by PVA, while formation of a bond between PVA and silica is indicated by the Si–O–C peak in the spectra of all the hybrids. The ability to form cross-linked nanofibers of PVA using thermally stable and relatively inert silica could broaden the scope of use of these materials in various technologies