To improve the interfacial bonding between halloysite nanotubes (HNTs) and poly(L-lactide) (PLLA), a simple surface modification of HNTs with L-lactic acid via direct condensation polymerization has been developed. Two modified HNTs were obtained: HNTs grafting with L-lactic acid (l-HNTs) and HNTs grafting with poly(L-lactide) (p-HNTs). The structures and properties of l-HNTs and p-HNTs were investigated. Then, a series of HNTs/PLLA, l-HNTs/PLLA and p-HNTs/PLLA composites were prepared using a solution casting method and were characterized by polarized optical microscopy (POM), field scanning electron microscopy, and tensile testing. Results showed that L-lactic acid and PLLA could be easily grafted onto the surface of HNTs by forming an Al carboxylate bond and following with condensation polymerization, and the amounts of the L-lactic acid and PLLA grafted on the surface of the HNTs were 5.08 and 14.47%, respectively. The surface-grafted L-lactic acid and PLLA played the important role in improving the interfacial bonding between the nanotubes and matrix. The l-HNTs and p-HNTs can disperse more uniformly in and show better compatibility with the PLLA matrix than untreated HNTs. As a result, the l-HNTs/PLLA and p-HNTs/PLLA composites had better tensile properties than that of the HNTs/PLLA composites.
The effect of polyethyleneimine (PEI) in precursor solution on the morphology and superconducting properties of YBa2Cu3O7-x (YBCO) films grown on LaAlO3 (LAO) substrates by metal-organic deposition (MOD) method was investigated. The morphologies of the YBCO films were different based on the different amount of PEI addition from 0.25 g to 0.9 g in 10 mL precursor solution. Furthermore, research results indicate that the PEI helps to improve the critical current density (Jc), the uniformity of surface morphology and c-axis orientation of thin film. The highest critical current density (Jc) of 2.17 MA/cm2 at 77 K is obtained in YBCO films fabricated on LAO substrates when the amount of PEI is 0.5 g in 10 mL precursor solution. YBCO layers with about 400 nm in thickness can be processed without cracks and holes during the whole heat treatment, which takes only 7.5 h.
Chemical solution-deposited (CSD) is a cost-effective non-vacuum method for YBCO coated conductor fabrication. We developed a new fluorine-free metal-organic deposition (MOD) method with metal acetates, propionic acid and xylene as the starting materials. Using this non-fluorine MOD method, we were able to get high performance YBCO superconducting films within a shortened heat treatment time, which was reduced by at Least 5 h in comparison with that for pyrolysis-annealing non-fluorine MOD process. Superconducting property, with a critial current density (Jc) over 0.55MA/cm2at 77K, self-field has been obtained for 380 nm epitaxial YBCO thin films on (00l) LaAlO3(LAO) single crystal substrate. Owing to the low price of starting materials and shorter heat treatment time, fluorine-free MOD method is a very effective and cost-cutting process.
Firstly, Magnesium oxide (MgO) whiskers were prepared by calcination of magnesium carbonate (MgCO3)whiskers which were obtained by solution method. Then, surface-grafted MgO whiskers with poly (L-lactide) were synthesized by bulk ring-opening polymerization ofL-lactide onto the surface of MgO whiskers. The MgO whiskers and surface-grafted MgO whiskers were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), x-ray diffraction (XRD) and fourier transformation infrared (FTIR). Results showed that MgO whiskers diameter in the range of 0.02-0.5μm, the length is between 10-80μm and well dispersed. A new characteristic stretching vibration absorption peak of C=O apppeared in the IR spectrum of the surface-grafted MgO whiskers, which suggested that poly (L-lactide) chains were successfully grafted on the surface of MgO whiskers.
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