Preparation Of Starch-Fe(III)/Al(III) Composite Hydrogel And Its Electric Field Response Properties

Under the action of the external electric field,the physical and chemical properties of the electro-responsive hydrogel will changes,its most important feature is to convert electrical energy into mechanical energy.For the preparation of high performance electro-responsive hydrogel,in this paper,soluble starch with large amount of hydroxyl groups was selected as raw material and glutaraldehyde as crosslinking agent.Starch-M(III)composite hydrogels were successfully prepared by adding different kinds of metal ions(M3+)to the system.The effects of metal ion species,content and electric field intensity on the electro-response of the hydrogels were discussed.Among them,hydrogels prepared in the presence of electric field are called A-hydrogels(E=0.4,0.8kV/mm)and without electric field are called B-hydrogels.The storage modulus of A-hydrogel and B-hydrogel were measured by dynamic viscoelasticity spectrometer(DMA),and the change of storage modulus(?G')and storage modulus change rate(?G'/G'B)react with electro-response of the hydrogels.The microstructure of the hydrogels were observed by scanning electron microscopy(SEM).Infrared spectra(FTIR)and thermo-gravimetric analysis(TGA)were used to study the gelling mechanism.The details are as follows:1.In the presence or absence of electric field,starch-Fe(III)hydrogels were successfully preparedby addinga series of different concentrations of FeCl3 solution to the soluble starch system(iron concentration were 0,0.05,0.1,0.15,0.2,0.25,0.3,0.35,0.4mol/L).The results showed that:when no electric field,the storage modulus of starch-Fe(III)hydrogel increases first and then decreases with the increase of iron concentration and the value of storage modulus reaches the maximum when the iron ion concentration is 0.15mol/L.After the electric field is applied,starch-Fe(?)hydrogels show positive response to an electric field,and the addition of iron ions promotes the electro-response.When the iron ion concentration is 0.2mol/L,the starch-Fe(III)hydrogels have the strongest electro-response.2.The starch-Al(III)hydrogels with different aluminum ion concentrations(aluminum ion concentrations were 0,0.05,0.1,0.15,0.2,0.25,0.3,0.35,0.4mol/L,respectively)were prepared by the same method.The mechanism of gel formation and the electro-response of hydrogels were studied and compared with starch-Fe(?)hydrogels.The results show that the addition of aluminum ions reduces the storage modulus of the hydrogels when the electric field was not applied,and the change of the storage modulus of hydrogels not obvious with the increase of the aluminum ion concentration.After the application of an electric field,starch-Al(?)hydrogels also have a positive electro-response similar with starch-Fe(?)hydrogels,and the addition of aluminum ions enhance the electro-response properties of starch hydrogel.It was found that both starch-Fe(?)hydrogels and starch-Al(?)hydrogels have positive response to the electric field by comparing the storage modulus(GB'),storage modulus change(?G')and storage modulus change rate(?G'/G'B)under different conditions and the electro-response properties were:starch-Fe(?)hydrogels>starch-Al(?)hydrogels.3.In the preparation of the starch-Fe(III)hydrogels and starch-Al(?)hydrogels,we found that with increasing concentration of iron ions,the value of storage modulus of starch-Fe(?)hydrogels first increases and then reduces.However,the storage modulus of the starch-Al(?)hydrogels did not change significantly with the increase of aluminum ion concentration.We speculated that because of the small content of aluminum ions in the system.In order to explore the impact of the aluminum ion content on mechanical properties and electro-response of the hydrogels,we changed the method for preparing starch-Al(?)hydrogels with higher aluminum ion contents(The contents of aluminum ions in the system were(wt%):0.25,0.5,0.75,1.0,1.25,1.5,1.75,2.0).The storage modulus of starch-Al(?)hydrogel decreases with the increase of aluminum ion content when E=0kV/mm.When the aluminum ion content is 2%,the system was sol instead of gel.But the system can still form hydrogel after the application of electric field.When the aluminum ion content reaches 2.5%,only the applied electric field strength is 0.8kV/mm can the system gel,but the storage modulus is only about 7kPa.It can be seen that increasing the content of aluminum ions not only affects the gelation process of the system but also promotes electro-response of the system.