Preparation And Thermo-Responsive Characteristics Of Positive And Negative Gating Membranes

As a part of intelligent materials, thermo-responsive gating membranes are getting more and more attentions. Thermo-responsive gating membranes can be traced to their potential applications in numerous fields, including drug delivery, chemical separation and tissue engineering, especially in new pattern targeting drug delivery systems (TDS), such as intelligent drug delivery systems and stimuli-responsive drug delivery systems, which continue to attract more and more attentions of scientific researchers. Although a lot of achievements have been made on the thermo-responsive gating membranes up to date, there are still many problems that need to be solved. For example, what effect has grafting yield on the performance of gating membranes and how could the responsive temperature of the gating membranes be adjusted to satisfy the need of different application cases? In some fields, negative gating membranes are preferred to positive gating ones. That is to say, the membrane water flux and solute diffusion coefficient should become smaller with the increase of environment temperature. In this thesis, investigations were systematically carried out on the preparation and thermo-responsive characteristics of positive gating membranes based on poly(N-iospropylacrylamide) (PNIPAM) and negative gating membranes based on the interpenetrating polymer network (IPN) between polyacrylamide (PAAM) and polyacrylic acid (PAAC), and some exciting results have been gotten.Poly(iV-isopropylacrylamide) (PNIPAM) is a preferable material for the preparation of positive gating membranes, because its lower critical solutiontemperature (LCST) is low and the responsiveness is fast. In this study, thermo-responsive positive gating membranes were prepared by grafting PNIPAM onto polyvinylidene fluoride (PVDF) membrane substrates with plasma-induced pore-filling grafting polymerization and a series of positive gating membranes with a wide range of grafting yields were prepared by changing the plasma power, concentration of NIPAM and grafting time. Effects of grafting yields on the membrane hydraulic permeability, solute diffusion coefficient and the change of pore radii by Hagen-Poiseuille's equation were investigated systematically for the first time. The results showed that the temperature break of membrane water flux and the pore size were about 32 and 31-37 respectively. The grafting yield heavily affected all of the water flux, the responsiveness coefficient and the thermo-responsive gating factor of membrane pore size. When the grafting yield was smaller than 2.81%, both the responsiveness coefficient (R) and the thermo-responsive gating factor of pore size (Nd,40/25) increased with increasing the grafting yield; when the grafting yield was between 2.81% and 6.38%, both the responsiveness coefficient (R) and the thermo-responsive gating factor of pore size (Nd,40/25) decreased with increasing grafting yield; however, when the grafting yield was higher than 6.38%, both the responsiveness coefficient (R) and the thermo-responsive gating factor of membrane pore size (Nd,40/25) were always equal to 1, i.e., no gating characteristics existed. It could be seen that the change tendency of the responsiveness coefficient (R) and the thermo-responsive gating factor of pore size (Nd,40/25) were the same with the increasing grafting yield, which illustrated the consistency between the change of water flux and the pore size of positively responsive membranes that based on PNIPAM with the change of environment temperature. The results also showed that the solute diffusion coefficient of positive gating membranes with low grafting yield (0.15%) increased with increasing environment temperature, the gating acted as "positive gating"; on the other hand, the solute diffusion coefficient of positive gating membrane with high grafting yield (6.46%) decreased with increasing environment temperature,the gating acted as "negative gating". In summary, in order to obtain a satisfactory gating property of the gating membrane, the grafting yield must be kept in a...