Preparation And Study Of Hydrogels Based On Sodium Alginate/Acrylamides

Intelligent hydrogels have broad prospects in the fields of molecular devices,biological medicine,sewage treatment,etc.and they attract a lot of attention.Temperature-sensitive hydrogels and pH sensitive hydrogels are two of them who are the most widely studied.In this paper,the intelligent hydrogels were prepared by using N-isopropyl acrylamide?NIPAM?,acrylamide?AM?,methylacrylic acid sodium?SMA?,and sodium alginate?SA?.With the UV-vis spectrophotometer spectroscopy,solid nuclear magnetic resonance,low field nuclear magnetic resonance,swelling ratio test,absorption test,I have researched the construction and performance of the materials.The specific work and results are as follows:1.By changing the values of AM/NIPAM in the gel system,I prepared a series of hydrogels whose LCST can be adjusted.With UV-vis spectroscopy,I researched the quantitative relations between monomer ratio and the LCST,the results showed that when the value of n_AM:n _NIPAMIPAM between 0⁰.25,the relation has good linear correlation,it's important for guiding the preparation of the materials.The result acquired from¹H NMR is consistent with the result from UV,the strength of signal for each segment in the gel will decrease obviously after LCST,the signal peak of water will split,and chemical shift will appear in spectrogram,it means that there are different state of water molecules,but due to the influence of hydrogen bond,chemical shift of H₂O will move to the high field.2.The temperature sensitive hydrogel SNA was prepared by situ polymerization with raw materials SA,NIPAM and AM in different proportions.When polymer electrolyte SA added in gel,the LCST decreased.Although there is a similar research about LCST mechanism,the discussion is not deep,so we not only study ¹H NMR spectra of the gel,but also make a deep discussions on T₁ and T₂.It turned out that the chemical group of different segment,will be affected by temperature differently,the main chain and those who close to the main chain,such as-NH-,are mainly influenced by steric hindrance when temperature is lower than LCST,but for those group who are in the end of the branched chain,the impact of temperature will be more serious,especially when the gel network structure shrinks.In the spectra of T₁,all the values of T₁ decrease at beginning,if temperature increases,the thermal energy of the molecular increases and the motility increases,if temperature is lower than the LCST,the motion of molecular is bound by the collapse of the gel microstructure,as the values of T₁ increase.In T₂ spectra,the values decrease,which means the motion of molecular recedes,especially temperature is higher than the LCST.But for the main chain and the chemical group close to the main chain,it without a turning point in T₂ values,that means the motility is no big different from beginning.Furthermore,by using low field nuclear magnetic resonance,I researched the distribution of T₂curve when gel SNA is swelling in water,the movement of water molecular and the motion of polymer chain segments are coordinated and the velocity of each is almost same,this kind of swelling behavior is called non Fickian model.3.I also studied the swelling performance of gel SNA,calculated the swelling model of gel in different media,analyzes the different characteristics of molecular movement.With the increase of the content of hydrophilic monomer AM,the equilibrium swelling ratios of gel SNA increase,and water retention will be better.The relationship between the swelling rate and temperature reflects the LCST characteristics of the gel SNA,which is similar to the results in former chapters.According to the theory of swelling dynamics,the most of swelling models for gel SNA in different mediums?water,1M NaCl solution,pH=1 solution?are non Fickian model,the difference is that their swelling index decreases respectively,and the swelling behavior has a trend from non Fickian model to Fickian model,so if there is a large number of metal ions or protons in solution,it will affect the motion rate of polymer chain during the process of swelling.4.For SA/P?AM-SMA?system,the swelling model is also non Fickian model.As the monomer SMA increases,the equilibrium swelling ratio of the gel increases,and when I add the physical crosslinking agent laponite,the swelling rate also increases,and the maximum value can up to 106.09g/g,if I still add laponite to the system,the crosslinking density of gels increases,which can reduce the swelling rate.Due to the large number of anionic groups in polymer,the gel can be used to adsorb methylene blue who is a kind of cationic dyes,with the increase of the amount of anion in the gel,electrostatic effect will increase and the adsorbing capacity also will increases.When adding laponite to gel system,the adsorbing capacity will increase,because the surface of laponite is full of negative charge,and the maximum adsorbing capacity can reach to 1089.4mg/g,if we still increase the content of crosslinking agent,the swelling rate will reduce and the quantity of adsorption also decrease,because the amount of dye which should be adsorbed by swelling is reduced.