| Biological gel typed Bionic Artificial Muscle(BAM)is a kind of electro active polymer.Under an applied DC electric field,it can produce reversible bending deflection and output force,which converts electric energy into mechanical energy isothermally.Based on the advantages of large deformation,high energy density,low quality,no noise,simple structure and low cost etc,the BAM has become a research hotspot in the field of innovation science and technology both foreign and domestick.However,at present,most of the BAM materials are synthesized artificially,but few people use natural polymers with good biocompatibility and complete biodegradability.Furthermore,there exists periodic tremor behavior in the process of electrically displacement and output force of the BAM,which seriously affects its work efficiency and stability.Therefore,in this paper,sodium alginate has been utilized to prepare the BAM,where the whole process is green,environmentally friendly,simple and reliable.Then the characteristics of output-force tremor of the BAM have been researched and summarized.The influence rules and mechanism of various technological factors on output-force tremor have been analyzed in depth,in order to improve the output force performance of the sample and promote its application development.(1)According to the sandwich-like structure of the BAM,three process factors affecting the output-force tremor have been proposed,i.e.ionic liquid doping,chitosan cross-linking and double-sided casting assembly.Then the BAM has been mainly made form sodium alginate,a natural polymer,and its green preparation process has been given in detail.The output-force tremor behavior and working life have been systematically defined.In view of the tremor duration,the output-force tremor behavior has been grouped into three categories:paroxysmal tremor,persistent tremor and permanent tremor.Three evaluation methods of the output-force tremor characteristics have been proposed.Subsequently,the property parameters and mechanical,electrochemical and microstructural characterizations of the specimens have been tested and analyzed on an experimental platform built.Based on orthogonal experimental design,size of the standard sample and the test voltage have been completed,which are recorded as 35 mm length-8mm width-1 layer thickness(0.352mm)-4V.(2)In the single and repetitive working cycle,the effects of ionic liquids doping process on the output-force tremor behavior of the BAM and its mechanism have been studied.In essence,it affects the internal porosity of the Gel Electrically Actuating Membrane(GEAM)and the amount of freely moving charged ions.When the amount of ionic liquid is 4ml,the GEAM is best modified,and its inner presents the ion channels with porous structure of70.47% porosity that is 1.4 times higher than that of the undoped membrane.The elastic modulus and internal resistance are the smallest about 1.871 MPa and 2.018? respectively,and the specific capacitance is the largest with 126.98 m F/g.Thus,the output force and its tremor behavior of the sample are optimized with 13.072 m N/g stable output force density and1720 s working life,which is severally 1.1 times higher and 19.5 times longer.In addition,the output-force performance of the sample is positively correlated with its conductivity,that is,the larger the stable output force is,the greater the current is,and vice versa.In air,its electro-output force and bending deflection have excellent reversibility and reproducibility.(3)Based on the single and repetitive working cycle,effects of the biological cross-linking process of sodium alginate and chitosan on the output-force tremor behavior of the BAM and its mechanism have been investigated.In essence,it affects the internal crystallinity of the GEAM.When the biological cross-linking ratio is 5:5,the GEAM is best cross-linked,and its internal polymer structure is fully coordinated and synergistic with26.08% crystallinity,which is 58.01% lower than that of the non cross-linked membrane.The elastic modulus and internal resistance are the smallest about 0.207 MPa and 1.616?respectively,and the specific capacitance is the maximum with 99.58 m F/g.Thus,the output force and its tremor behavior of the sample are optimized with 7.213 m N/g stable output force density and 1020 s working life,which is severally 35.94% higher and 5.6 times longer.Furthermore,the qualitative relationship between bending deformation force,through current and bending stiffness of the BAM has been derived by mathematical expression.(4)During the single and repetitive working cycle,the influence of double-sided casting assembly process on the output-force tremor behavior of the BAM and its mechanism have been researched.In essence,it forms a permeable layer between the inner gel layers and reduces the interface contact resistance.When the double-sided casting temperature is 50?,the gel membrane of each layer is achieved the best connection.The thickness of permeable layer at the interface between the inner gel layers reaches the maximum of 6?m.Then the water loss rate,the elastic modulus and the internal resistance are all the smallest,respectively about 0.176%,5.934 MPa and 1.91?,and the specific capacitance is the largest with551.34 m F/g.Thus,the output force and its tremor behavior characteristics of the sample have been optimized,that is,the stable output force density of 16.249 m N/g(increased by 1.6 times)and working life about 891s(extended by 9.6 times).Meanwhile,this process factor has effectively promoted the accumulation of hydrated charged ions and the retainability of their migration rate in the GEAM.(5)The mathematics model on the effect of the permeable thickness at interface between the inner gel layers on the mechanical property of BAM has been established.Starting from the research of sandwich-like structure and failure mechanism of the sample,the cantilever beam model with gradient permeable interface layer has been obtained.According to the general law of linear elastic plane problems,the stress equilibrium differential equation,geometric equation,physical equation and strain compatibility equation have been studied.Then the stress function method and the approximate theory of cantilever beam have been used to deduce and establish the bending stress and displacement equations of the BAM.Combining with its bending deformation force formula,the mechanical impact model based on the thickness of permeable interface layer has been built successfully.Subsequently,the analytical solution of bending stress has been calculated from the performance parameters of each specimen,whose variation trend was opposite to the actual output force,respectively.This fully confirmed that when bending deformation force was constant,the bending stress inside sample was negatively correlated with its actual output force.As the total membrane thickness was fixed,increasing the permeable thickness of the interface layer of the BAM gel membrane could significantly improve the output force and its tremor behavior characteristics.Namely,the bending stress was small,the bearing capacity was strong and the deflection displacement was large,so the fatigue failure was difficult with high working stability. |
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