Investigation On The Preparation And Performance Of Smart Hydrogel Based On Polyion Complex

Smart hydrogel is a class of novel material with unique stimuli-responsive ability that attracted extensive investigates interest in various fields,including controlled drug release,microfluidic device,bio-sensor,etc.Among the family of smart hydrogels,p H-responsiveness is one of the most study sub-classes.The hydrogels composed of weak polyelectrolyte occupies the majority of p H-responsive system,their responsive behavior is well understood,that is,they exhibit abrupt volume expansion or shrinkage around certain p H.Moreover,these polyelectrolytes(PE)also possess the ionic strength-responsiveness and reduced their volume as the ionic strength increases.There are two other types of hydrogel composed by polyampholyte(PA)or polyion complex(PIC)also show characteristic p H-and ionic strength-responsive behavior,however,they have gain less concern that the PE hydrogel due to certain problems.The PA hydrogel is highly sensitive to the monomer ratio and lead to the poor reproducibility from run to run.Whereas most of the PICs are prepared by mixing two oppositely charged polymers in dilute solution,which is difficult to predict the composition,therefore,the systematic study on PIC's responsiveness is impossible.In this thesis,we utilized an alternative route to prepare the PIC in a controllable manner to overcome the abovementioned problem and conduct a systematic investigation on the mechanical performance,p H-and ionic strength-responsive characteristics of PIC hydrogel,the result is summarized as followed:1,The PIC hydrogel composed of polyacrylic acid(AAc)and poly(2-(dimthylamino)ethyl methacrylate)(PDMAEMA)is prepared by direct polymerization of DMAEMA in the PAAc aqueous solution.In this way,the composition of PIC can be easily tuned by changing the ratio of DMAEMA to PAAc in the pre-polymerization solution.Based on the water content on equilibrium,we found that the different preparation conditions and various charge ratios have lead to insignificant divergence in the result,which is superior to PA hydrogel considering the further study.Besides,the viscoelastic measurements and tensile tests indicated the physical crosslinking nature of PIC hydrogel and demonstrated the good mechanical performance and self-healing ability.2,In the ionic strength-responsive test,the unique positive behavior of PIC hydrogel was realized,that is,the volume of PIC hydrogel increase as the ionic strength increase.In specific,the swelling ratio of PIC is beyond 2 000 % as the concentration of sodium chloride exceeds 1.5 M;and a gel-to-sol transition is occurred at the 3.3 M Na Cl solution.Moreover,the concentration in feed is demonstrated to be irrelevant to the responsive behavior,meanwhile,the introduction of chemical crosslinker do not alter the general behavior but do reduce the swelling degree and improve the mechanical performance of swollen hydrogel.3,In the p H-responsive test,the unique characteristic of PIC hydrogel is observed,its responsive curve turns to be a U shape,in other word,the PIC hydrogel is dually p H-responsive,it can be triggered to expand in acidic condition as well as in basic environment.Further investigation has found i)the p H-responsive behavior is independent to the concentration in feed;ii)the charge ratio variation do not change the dually responsive characteristics but do tune the swelling ratio in certain degree;iii)the unique dually p H-responsiveness is preserved after the addition of chemical crosslinker,however,the formation of permanent network has reduced the swelling ratio of PIC hydrogel in strong acidic or basic circumstances and enhanced its mechanical strength at swollen state.Compared to PE hydrogel,PIC hydrogel possesses one more “trigger”;with regard to PA hydrogel,PIC hydrogel is more controllable.In conclusion,the polyion complex hydrogel exhibits unique p H-and ionic strength-responsive behavior,possesses good mechanical performance and self-healing ability,can be fabricated by facile and controlled method,all of these advantages indicate its bright future in the theoritally modeling as well as in the various applications.