Preparation And Performance Of Polyacrylic Acid IPN Hydrogels

The characteristics of hydrogels occur continuous or discontinuous changes withthe changing of environment such as chemical, ion strength, temperature, electric field,light, mechanical stress, and so on. Because of their excellent biocompatibility,hydrogels have attracted a lot of attentions in many fields, such as biological medicine,intelligent drug delivery system, chemical converter, sensor, artificial muscle,chemical memorizer, molecular separation systems, et al. In the past decade, thehydrogels were combined with the nolinear chemical oscillating systems bytransformation the chemical energy of oscillating system into the mechanical energyof hydrogels and a novel kind of hydrogels named self-oscillating hydrogels wereobtained. The physical and chemical characteristics of the new kind of hydrogelschange periodically along with the chemical oscillating reactions. Because the newhydrogels can realize the phase change without any external stimuli, so they are called“self-oscillating hydrogel”. For the special properties, the hydrogels have been used inindependent transmission surface, automatic rotation motor, et al.Chapter I: IntroductionThe definition, classification and application of smart hydrogels were reviewed inbrief. The design mechanism and development of self-oscillating hydrogels were alsointroduced in this part.Chapter II: A conversion behavior of PEG/PAA gel in Fe3+/citric acid solution insunlightA novel phase transition behavior of PEG/PAA gel was firstly observed involving acontrollable conversion from gel to sol when it was immersed in solution containingFe3+ions and citric acid under sunlight radiation for a certain time. The transformationprocess could be controlled effectively by changing the ratio of Fe3+concentration tocitrate acid concentration and the pH of the solution. This phenomenon occurred onlywhen the concentration ratio was less than1:2and the value of pH was in the range of1~6. In addition, the sol would change into gel again if metal cations, such as Fe3+,Al3+, Ce4+were added into the system. The new characteristics of the gel may make itbecome a perfect material in the drug release, cell culture, and so on. Chapter III: Synthesis and characterization of self-oscillating PAA/PEG IPNhydrogel based on a pH oscillator in closed systemA pH responsive interpenetrating polymer network (IPN) PAA/PEG hydrogels wereprepared by using radical polymerization with two-steps method. The IPN hydrogelswere characterized by FTIR spectroscopy and morphological analysis with SEM. Theresults indicated that the chains of PEG and PAA twined forming porous structure isbeneficial for water molecules entering inside of the hydrogels. In addition, thepH-responsive behavior, salt sensitivity, oscillatory swelling/deswelling behaviors andself-oscillation in bath pH oscillator were also studied. The results showed that theprepared hydrogels exhibited pH-sensitivity, good swelling/de-swelling reversibility,and excellent salt sensitivity. The research highlights self-oscillations ofswelling-de-swelling for the polymer hydrogels were realized by coupling pH changein the external solution media. This study may create new possibility as biomaterialincluding new self-walking actuators and other devices.Chapter IV: Synthesis and characterization of self-oscillating P(AA-co-AM)/PEGsemi-IPN hydrogel based on a pH oscillator in closed systemVarious interpenetrating polymer network (IPN) hydrogels composed ofpore-forming agent polyethylene glycol (PEG), acrylic acid (AA) and acrylamide(AM) were prepared by using free radical polymerization with a two-step method.The chemical structures of the synthesized hydrogels were characterized by FTIRspectroscopy and the morphologies were studied by scanning electron microscopy(SEM) method. The swelling properties, such as the pH-responsive behavior, saltsensitivity, oscillatory swelling/de-swelling behaviors in different solutions withvarious pH values and self-oscillating behaviors in bath pH oscillator wereinvestigated in detail. The results revealed that the prepared hydrogels exhibited highpH sensitivity and excellent salt sensitivity when the pH values of the mediumchanges from3.0and7.0and well reversible property by undergoing a number ofswelling/de-swelling recycles. In particular, the hydrogels exhibited self-oscillationbehavior in a closed system containing BrO3--SO32--Fe(CN)64--H+. This study maycreate a new possibility as biomaterial including new self-walking actuators and otherdevices.