RESUMO
ZrO2 was coated on AZ31 magnesium alloy substrate by plasma electrolytic oxidation with K2ZrF6 and NaH2PO4 electrolytes. The discharge characteristics and variation in active species during the plasma electrolytic oxidation (PEO) process were studied by optical emission spectroscopy. The surface morphology and element composition of the membranes were observed by scanning electron microscope. The ion transfer of the substrate was studied by atomic absorption spectroscopy. The phase composition and corrosion characteristics of the PEO membranes were examined with XRD and an electrochemical workstation, respectively. The heat and mass transfer models during the PEO process were introduced. The contributions of ions to the membranes and active species were also analyzed. The results indicated that the ion transfer at different stages exhibits different tendencies. At the first and transition stages, the migration resistance of the ions was low and increased gradually. At the initial discharge stage, the migration resistance was the highest because the highest membrane growth rate occurred at this stage. At the later discharge stage, the migration resistance tends to be stable, which is ascribed to a dynamic equilibrium PEO membrane growth rate. The intensity of active species is related to the energy state of the working electrode's surface. The higher the energy, the greater the probability that the active species will be excited to generate energy level transitions, and the higher the plasma concentration.
RESUMO
Processing robust mechanical properties is important for elastomeric materials. In this work, different molecular weights of polyethylene glycols (PEG) were used to modify graphene oxide (GO) in order to study the relationship between the number of hydrogen bonds and the properties of the polyurethane/graphene oxide membrane. The fact of PEG was successfully grafted onto the surface of GO was certified by Fourier transform infrared spectra, Raman spectra, X-ray photoelectron spectroscopy. The graft ratio was indicated by thermogravimetric analysis. The presence of hydrogen bonds in PUR/MGO composites membrane was proved by the cyclic loading-unloading test and stress relaxation test. The thermal stability and low-temperature resistance performance of PUR/MGO had been improved compared with PUR/GO. When the molecular weight of PEG grafted on the surface of GO was 600, the tensile strength and elongation at break of the composite membrane were optimal. The reason for the improvement of physical and mechanical properties was that the dispersion of filler in the rubber matrix and the compatibility between filler and rubber had been improved.
RESUMO
Transgenic animal mammary gland bioreactors are being used to produce recombinant proteins with appropriate post-translational modifications, and nuclear transfer of transgenic somatic cells is a more powerful method to produce mammary gland bioreactor. Here we describe efficient gene transfer and nuclear transfer in goat somatic cells. Gene targeting vector pGBC2LF was constructed by cloning human lactoferrin (LF) gene cDNA into exon 2 of the milk goat beta-casein gene, and the endogenous start condon was replaced by that of human LF gene. Goat fetal fibroblasts were transfected with linearized pGBC2LF and 14 cell lines were positive according to PCR and Southern blot. The transgenic cells were used as donor cells of nuclear transfer, and some of reconstructed embryos could develop to blastocyst in vitro.