Investigation Of The PH-sensitivity And Release Behavior Of Polyacrylamide Hydrogels

Polymer hydrogels with stimuli-responsive swelling behavior have been widely used in the field of chemical industry, medicine, agriculture, biology and so on. The investigation of hydrogels will be quite valuable not only for the pure research but also for the application. In the thesis, two aspects have been mainly studied. One is the pH-sensitivity of polyacrylamide hydrogels. The causes of swelling have been summarized. Swelling ratio is calculated by the expressions, which is deduced in the part 2 of the paper. The other asPect is the release character of polyacrylamide hydrogels incorporated with polyaniline. The released concentration of polyaniline can be controlled through the expressions deduced in the part 3 of the thesis. The formula for calculating the released concentration and the coefficient of diffusion have also been discussed in the part 3 of the thesis.1. Polyacrylamide hydrogels with different composition were prepared and characterized. Due to the different of swelling ratio, the process of pH-sensitivity can be divided into 3 regions. When the pH value is from 0 to 7, the value of swelling ratio of gels is very low and grows slowly (regions 1). When the pH value is from 11 to 13, the value of swelling ratio has its maximum (regions 2). When the pH value is bigger than 13, the value of swelling ratio is rapidly attenuated (regions 3). The main cause of swelling of ionic hydrogels is the electrostatic repulsive force, which is induced by the ionization of ionic group of Polyacrylamide hydrogels. Besides electrostatic repulsive force, osmotic pressure, interaction between gels and solvent will also be important for the swelling. Based on the Flory's theory of swelling of ionic hydrogels, expressions of the swelling ratio have. been deduced. The expressions are helpful for controlling and forecasting the swelling ratio of ionic hydrogels.2. polycrylamide- polyaniline blend hydrogels with different composition were prepared and characterized. The result of experiments show that polyaniline do not influence the pH-sensitivity of polyacrylamide hydrogels, so the expressions used to calculate the swelling ratio of polyacrylamide hydrogels can also be used for calculating the swelling ratio of polycrylamide- polyaniline blend hydrogels. The released concentration of polyaniline is decided by two parameters, one is the coefficient of diffusion, and the other is radius of swelled hydrogels. Based on the relationship between the released concentration and the two parameters, the formula has been deduced. Through the formula the released concentration of polyaniline can be easily forecasted, before the hydrogels are synthesized.