yongyi yao

Radical grafting of acrylic acid (AA) monomer onto the aromatic polyamidereverse osmosis (APRO) membrane was performed. The physical adsorption byfree radical initiator technique was applied to modify the surface of theasymmetric membrane. The hydrophobic initiator adsorbed on the APRO membranewas used to initiate the water-soluble monomer in aqueous phase. The APROmembrane was immerged into ether solution of benzoyl peroxide (BPO). The BPO wasphysically adsorbed onto the membrane surface. The hydrophobic initiator wasinhibited to diffuse through membrane surface into the aqueous solution of the acrylicacid monomer because of a hydrophilic/hydrophobic barrier. The grafting process wastriggered by the residing BPO on the membrane surface in an aqueous medium at70°C for a certain time interval. The surface changes of grafted membrane werecharacterized with ATR-FTIR, SEM, AFM and contact angle measurements. The resultsshowed the PAA is successfully grafted on the APRO membrane surface. When thegrafting rate of PAA was increased from 0% to 8.02%, the edge of leaf-like surface ofAPRO membrane was gradually curled and the roughness of APRO membrane wasdecreased about 36% (Ra). These changes of membrane surface increased thehydrophilicity of the APRO membrane surface and the contact angle decreased byabout 50%.

The ionic liquid of 1-butyl-3-methyl-imidazolium bromide ([BMIM]Br) was used asa good solvent to dissolve polyacrylonitrile (PAN). In order to systematically studythe rheological properties of PAN/[BMIM][Br] solutions, the shear rheology ofPAN/[BMIM][Br] solutions with a concentration range of 3.0-6.0 wt% was investigatedby measuring the complex and dynamic moduli at different temperatures. The effectsof solution concentration and temperature on the complex viscosity of PAN/[BMIM][Br]solutions were studied. The solutions exhibited shear-thinning behaviours. Thecomplex viscosity of solutions increased with increase in solution concentration. Theheightening of solution temperature lowers the complex viscosity of the solution. Thenthe storage modulus, G′, and loss modulus, G′′, influenced by the PAN concentrationare discussed. Both G′ and G′′ are increased with the increasing in PAN concentration.The crossover frequency of G′ to G′′ is shown to decrease as the concentration isincreased. Master curves are generated for complex viscosity by employing Carreauand Cross models to fit the experimental data. Both Carreau and Cross models yieldgood shifted curves for the complex viscosity. The activation energy for each solutionconcentration was calculated from the Arrhenius plots of the shift factors with respectto temperature. The activation energy for PAN/[BMIM][Br] solutions varies between4.79 and 8.88 kJ/mol, being slightly higher for the Cross model. The activation energyis increased with the increase in PAN concentration. It can be summarized that 3-5 wt%range of PAN/[BMIM][Br] solution concentrations are considered as dilute solutions, inwhich PAN molecules are independent of each other without any intermolecularentanglement.

Poly(vinyl alcohol) (PVA) ultrafine fibres were prepared by gas-jet/electrospinning of its aqueous solutions. The morphology of the gas-jet/electrospun PVA fibres was investigated by controlling parameters such as: polymer solution concentration,gas flow rate and the polymer solution feeding rate. The morphology of the PVA fibres changed when the solution concentration was increased from 7 wt% to 12 wt%. With concentration of 7 wt%, a combination of smooth and some beads ultrafine PVA fibres was observed. With higher concentration, smooth fibres were obtained and the beads disappeared. The average diameters of PVA fibres increased gradually from 165±4 nm to 263±8 nm with the concentration from 7 wt% to 12 wt%. In addition, the average diameters of these ultrafine fibres were decreased from 317±10 nm to 219±5 nm after an initial increase in the gas flow rate from 2.5 L/min to 7.5 L/min and then increased to 287±9 nm as the gas flow rate increased to 10.0 L/min. The morphologicalstructure changed with the variety of the solution feeding rates. At the solution feeding rate of 3.3 mL/h, PVA fibres with beads were observed. The average diameters of PVA fibres increased with increasing solution feeding rate. Particularly, the production rate of the gas-jet/electrospinning of PVA solution could be up to 2.2 mL/h, which was 11 times higher than the conventional electrospinning (0.2 mL/h), while the difference between the average diameter of electrospun fibres and the gas-jet/electrospun fibres was slight.

Poly(ethylene terephthalate) (PET) nanofibres were prepared by gas-jet/electrospinning of its solution of 15 wt% concentration in the mixture of phenol and 1,1,2,2-tetrachloroethane (50/50, w/w). The morphologies of gas-jet/electrospun fibres collected on a clean stainless steel plate and three different coagulation baths were observed under a scanning electron microscope. These coagulants were water, ethanol and the mixture of water and ethanol: 50/50 (v/v). Preliminary study on the effect of different coagulation baths as collector on the morphology of gas-jet/electrospun PET nanofibres was carried out. In particular, on the surface of the fibres obtained from the water coagulation bath, many short branches appeared. The beaded fibres were evident in the SEM image of the PET nanofibres collected in an ethanol bath. Smooth fibres without bead can be obtained using mixture of water and ethanol: 50/50 (v/v) as the coagulation bath. The average diameters of fibres collected in water, ethanol and water/ethanol bath, were 87, 105 and 84 nm, respectively. Compared with the average diameter (90 nm) of fibres collected on a metal plate, the diameter of fibres collected in water and water/ethanol coagulation baths decreased, while the diameter of fibres collected in ethanol bath increased. Among three coagulants, the morphology and the average diameter of PET nanofibres collected in the mixture of water and ethanol was best and thinnest, respectively.