Effect of Material Composition on Tunable Surface Roughness of Magnetoactive Elastomers

Abstract

We investigated magnetic-field-induced modifications of the surface roughness of magnetoactive elastomers (MAEs) with four material compositions incorporating two concentrations of ferromagnetic microparticles (70 wt% and 80 wt%) and exhibiting two shear storage moduli of the resulting composite material (about 10 kPa and 30 kPa). The analysis was primarily based on spread optical reflection measurements. The surfaces of all four materials were found to be very smooth in the absence of magnetic field (RMS roughness below 50 nm). A maximal field-induced roughness modification (approximately 1 μm/T) was observed for the softer material with the lower filler concentration, and a minimal modification (less than 50 nm/T) was observed for the harder material with the higher filler concentration. All four materials showed a significant decrease in the total optical reflectivity with an increasing magnetic field as well. This effect is attributed to the existence of a distinct surface layer that is depleted of microparticles in the absence of a magnetic field but becomes filled with particles in the presence of the field. We analyzed the temporal response of the reflective properties to the switching on and off of the magnetic field and found switching-on response times of around 0.1 s and switching-off response times in the range of 0.3–0.6 s. These observations provide new insight into the magnetic-field-induced surface restructuring of MAEs and may be useful for the development of magnetically reconfigurable elastomeric optical surfaces.

Effects of Filler Distribution on Magnetorheological Silicon-Based Composites

“…3. Increasing the magnetization, a strong alignment within the fillers results in an anisotropic distribution of the particles [34,35,36,37,38,39].…”

Tunable Drop Splashing on Magnetoactive Elastomers

“…As reported in our recent paper, under the top surface of MAEs, there exists a thin (≈20 µm) depletion layer with a reduced concentration of magnetic microparticles. [ 28 ] The effect of magnetic field on elastic properties of this depletion layer can be different from its effect on the bulk medium.…”

“…[ 22 ] However, recently it has been realized that surface properties of MAEs are significantly modified in a magnetic field too. In particular, the wettability, [ 23–27 ] the surface roughness, [ 28–33 ] the adhesive properties, [ 23,24,34 ] and the friction phenomena [ 35–37 ] were all found to be strongly dependent on a magnetic field.…”

Magneto-Rheological Elastomer Composites. A Review

“…Just the micro-sized iron particles, with high saturation magnetization, show a considerable orientation effect within a magnetic field. In fact, due to their large magnetic moment, they generate strong attractive dipole-dipole interactions when the magnetic field is applied [40,41]. Furthermore, close contact is also decisive to get these dipole-dipole interactions in the magnetic field [42].…”