Improving thermal stability of TEMPO‐oxidized cellulose nanofibrils (TOCNs) is a major challenge for the development and preparation of new nanocomposites. However, thermal degradation of TOCNs occurs at 220 °C. The present study reports a simple way to improve thermal stability of TOCNs by the heat‐induced conversion of ionic bonds to amide bonds. Coupling amine‐terminated polyethylene glycol to the TOCNs is performed through ionic bond formation. Films are produced from the dispersions by the casting method. Infrared spectroscopy and thermogravimetric analysis confirm conversion of ionic bonds to amide bonds for the modified TOCN samples after heating. As a result, improvement of TOCNs' thermal stability by up to 90 °C is successfully achieved.
The recent study focusing on paper coated with microfibrillated cellulose (MFC) revealed the ability of such a structure to achieve a controlled release of molecules introduced into its nanoporous network. The present study examines this concept using a chlorhexidine digluconate-based (CHX) antibacterial solution. Various analyses were performed, optical microscopy, FE-SEM and AFM to underline the structure of the nanoporous MFC network. Release studies were conducted in an aqueous medium following two different protocols and antibacterial tests were done to evaluate the efficiency of the final materials obtained. MFC coating provided a slower and more progressive release of CHX. Indeed, papers impregnated with CHX were active for 18 days, whereas papers coated with CHX/MFC retained their antibacterial activity for 45 days. In parallel, similar tests were carried out using a model coating slurry, and although the rate of release of CHX was also slowed down, the quantities released were insufficient to confer any antibacterial activity. In conclusion, this study suggests that the use of MFC as a coating could be very promising since it allows a controlled and progressive release of molecules preserving long-term antibacterial activity. 相似文献
A two-pulse degenerate four-wave mixing experiment is analyzed in the case where the medium under investigation can be modeled by two-level systems having unequal permanent dipole moments. By modeling the light pulses by double exponentials [exp(-Gamma/t/)], we give an analytical expression of the third-order nonlinear polarization of the medium. We apply this result to simulate the measured signal in such experiment. We show that in the case of a two-photon transition, a signal can be detected if the pump pulse interacts with the medium before the probe pulse contrary to what is observed for excitations in the resonance region. An attempt to explain this behavior is made and the detected signal is analyzed in terms of pure coherent processes. This effect appears as a signature of the presence of permanent dipole moments. To test this property on a more realistic system, we then have considered a one-dimensional frequency-selected infrared degenerate four-wave mixing experiment on a molecular anharmonic vibrational mode modeled by a Morse potential and coupled to a dissipative bath of harmonic oscillators. We show that the two-photon transitions allowed by the presence of permanent dipole moments enable to analyze the multilevel system dynamics as if they were the one of a two-level system. Our results can also be extended to the case of inhomogeneous broadening and are of interest to study the infrared photon-echo response of anharmonic vibrational modes. 相似文献
The structural and electronic transport properties of La1−xCexMnO3 (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with
Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration
up to 50% doping. The system La0.5Ce0.5MnO3 also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition. 相似文献
