Tham khảo tài liệu 'electroactive polymers for robotic applications - kim & tadokoro (eds.) part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Active Polymers An Overview 13 Magnetically Activated Polymers Sensitive polymeric materials showing strain due to changes in the magnetic field are called magnetoelastic or magnetostrictive polymer materials also often called ferrogels. The gradient of the magnetic field applied acts as the driving force 26 . A magnetic field induces forces on all kinds of materials solid materials experience more forces than fluids. By combining fluidlike and solidlike properties in a material the effect of magnetic force can be enhanced 3 . A magnetocontrolled medium can be considered a specific type of filler-loaded swollen network. Ferrogels are a chemically cross-linked polymer network swollen by a ferrofluid which is a colloidal dispersion of monodomain magnetic particles. In these gels the magnetic particles are attached to the polymer chains by strong adhesive forces 26 . Under a uniform magnetic field no net forces are observed on the gel except the Einstein-de Haas effect which is caused by a change in the magnetic field vector. When these gels are subjected to a magnetic field gradient the particles experience a net force toward the higher magnetic field. These particles carry the dispersing fluid and polymer network with them producing a macroscopic deformation of the gel. Elongation contraction bending and rotation can be obtained depending on the geometric arrangement of these materials. With their ability to create a wide range of smooth motions along with quick operation and precise controllability these magnetic fields controlling soft and wet gels show good promise in the development of stimuli-responsive gels and actuators 26 . Electric and magnetic field-induced shape and movement was obtained in a polymer gel with a complex fluid as the swelling agent. Magnetic particles were incorporated into poly A-isopropylacrylamide and poly vinyl alcohol gel beads. The beads aligned as a chainlike structure in uniform magnetic field lines and they aggregated in a .
