| Dielectric elastomer(DE)is a kind of electro-driven smart soft material.The actuation of DE is featured with a very large strain and extremely fast response.Thus,It has important application prospects in cutting-edge technology fields such as artificial muscles and soft robotics.Polymer elastomers generally have low dielectric constant and low breakdown field strength,which limits the electromechanical performance.Inorganic nano particles with high dielectric constant have been compounded to prepare organic/inorganic nano composite dielectric elastomer.The incoporation of the inorganic nanoparticles could effectively improve the dielectric constant,but usually reduced the breakdown field strength and greatly increased the modulus.As a result,the electromechanical performance were not enchanced much.In the current work,a block oligomer dispersant was designed and synthesized.With the dispersant,the nano-BaTiO3 particles were effectively dispersed in the acrylate block copolymer elastomer to prepare a high-performance dielectric elastomer composite material.The main results are as follows:(1)Through RAFT solution polymerization,we designed and controlled synthesis of a series of acrylic-b-styrene diblock oligomer(AAmStn)dispersants with different structures.It was found that the dispersing performance of the dispersant is significantly better than the commonly used oleic acid dispersant.With mass ratio of AA20St5 to BaTiO3 to be 1/2,the nanoparticles of BaTiO3 were able to be well dispersed in tetrahydrofuran so that the diameter of BaTiO3 after dispersion was measured to be about 150nm.(2)The synthesized-by-design styrene-b-butyl acrylate-b-styrene(SBAS)was dissolved in a well-dispersed BaTiO3 tetrahydrofuran dispersion,which was cast to fabricate a nanocomposite dielectric film.We found that the diblock oligomer dispersant greatly improved the compatibility and dispersibility of the nanoparticles in the polymer matrix.Compared with the system without the dispersant,the mechanical properties and electromechanical performance of the composite films were greatly improved.As the mass content of barium titanate particles in the composite material increases from 0 to 30wt%,the modulus of the composite films first steadily increased,and then increased rapidly above 15wt%.The tensile strength and elongation at break only slightly decreased.The electrical constant increased steadily from 4.8 and rapidly increased to 62 at 30wt%.The dielectric breakdown strength first increased from 49V/?m and then decreases.At 15wt%,a maximum value of 89V/?m was reached.The highest electro-driving deformation of the composite film was obviously larger than that of pure elastomer film.Upmost,the actuation strain could be increased by 3 times(from 10%to 40%).At a given acuation electric field,the actuation strain showed a complex trend of first increasing,then decreasing,and then increasing again with the change of the nanoparticle levels.(3)With two sets of synthsized by-design SBAS and styrene-b-isooctyl acrylate-b-styrene triblock copolymer(SEHAS),we studied the influence of the length and type of the soft block on the mechanical properties,dielectric properties and actuation performance of the composite dielectric films.It was found that adding 10wt%of well-dispersed nanoparticles could simultaneously increase the dielectric constant and breakdown field strength.With the increase of the soft segment length,the dielectric constant of the composite dielectric film increased but the modulus decreased and thus the driving performance improved.Since SEHAS has higher stress hardening behavior than SBAS does,SEHAS/BT composite film exhibited higher driving performance.The composite of SEHAS with molecular weight for each block 15k-120k-15k exhibited the maximum actuation strain as high as 190%under 105V/?m.The composite of SEHAS with molecular weight for each block 15k-210k-15k exhibited a maximum actuation strain of 60%under a low electric field of 28V/?m.It is suggested that SEHAS/BT should be a high performance DE material. |
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