Studies On PVA/PAA Hydrogel Fibers And Its Stimuli-Responsive Behavior

PVA/PAA hydrogels is kind of the most representative responsive polymer gels, and can be made to use in various fields, including chemical actuator, artificial muscle, drug transform and delivery system, specialized separation system and chemical value, etc. From the point of preparation, All the PVA/PAA hydrogels reported were obtained in films or moulds. PVA has good solution spinnability and compatibility with PAA. Therefore, we designed to prepare responsive PVA/PAA hydrogel fibers by solution spinning and then to study the stimuli-responsive behavior of the hydrogel fibers in environmental electrolyte solution. The main contents are listed below:1 Three kinds of PAA gel fibers with different networks were preparedThree kinds of PVA/PAA hydrogel fibers were firstly obtained by solution spinning followed by crosslinking technology: The thermo-induced PVA/PAA gel fiber with stereo-crosslinking network was prepared via solution wet-spinning followed by thermally heating the dried fiber; The PVA/PAA semi-interpenetrating network gel fiber was prepared via solution wet-spinning followed by chemically crosslinking PVA with glutaraldehyde; The PVA/PAA interpenetrating network gel fiber was prepared via solution wet-spinning followed by chemically crosslinking PVA with glutaraldehyde and crosslinking polymerization of AA monomer.2 pH-sensitive behavior of thermo-induced PVA/PAA hydrogel fiber were studiedThe swelling/deswelling hysteresis phenomenon of the thermo-induced PVA/PAA hydrogel fiber with the circular change of pH in environmental solution was firstly reported and the hysteresis mechanism was also discussed. The effects of PAA content within the network and the network crosslinking density on the swelling and swelling junction behavior of the fiber with the change of pH in environmental solution were studied. The morphology structure of thermo-induced PVA/PAA gel fibers were studied via TEM and SEM. It is examined that there occurs phaseseparation and PAA can move into the coagulation during the process of the solidifying of the dope filament. The phase separation within the blending system may intensely influence the swelling junction behavior of the hydrogel fiber.3 Bending behavior of the thermo-induced PVA/PAA hydrogel fiber under D.C. electric stimulus were studiedThe bending behavior of the thermo-induced hydrogel fibers under environmental solution and a series of parameters such as composite, structure of the gel network and the properties of the environmental solution were firstly studied. The experimental results showed that the equilibrium bending degree and the bending speed of the fibers increased with increase of the PAA content within the gel network and the applied electric voltage and decrease of the fiber's diameter; Within the range of concentration of the crosslinking agent, pH and ionic strength in the solution examined in this study, both the bending degree and the bending speed have a peak value occurring. These observations are interpreted in terms of fiber stiffness, fixed charge density, and swelling pressure, which depend on the hydrogel equilibrium states in different pH and ionic environments along with the electrochemical reactions under direct current electric field.4 Swelling/deswelling behavior of thermo-induced PVA/PAA hydrogel fibers in salt aqueous solutions were studiedThe swelling/deswelling behavior of the thermo-induced hydrogel fibers depend on its composite, structure and properties of the environmental solution. Experimental results indicated that the swelling ratio in deionized water increased with an increase in the PAA content within the composite hydrogel. The swelling ratio decreased with increase of ionic strength in chloride salt aqueous solutions, owing to the osmosis of water and ions between the polymeric gel and the external solution. Comparing to the univalent salt solutions, the swelling degree of the fiber in multivalent solution decreased obviously. Also these swelling orders are related to the hydration radius of th...