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.
Highlights
Magnetoactive elastomers (MAEs), known as magnetorheological elastomers (MREs) in the context of mechanical applications, are smart materials composed of micrometer-sized ferromagnetic particles embedded in a soft polymer matrix [1,2,3,4,5,6,7,8,9,10,11]
The polymer matrix of the investigated MAEs is made of the base polymer VS100000 (vinyl-functional polydimethylsiloxane (PDMS)) for addition-curing silicones and the reactive diluent polymer MV 2000 combined with the chain extender modifier 715 (SiH-terminated PDMS; all these materials were provided by Evonik Hanse GmbH, Geesthacht, Germany) and silicone oil AK10
Such a low surface roughness is explained by the existence of a topmost polymeric surface layer that is a low surface roughness is as explained existence of layer a topmost polymeric thatthe is depleted of microparticles, depictedby in the
Summary
Magnetoactive elastomers (MAEs), known as magnetorheological elastomers (MREs) in the context of mechanical applications, are smart materials composed of micrometer-sized ferromagnetic particles embedded in a soft polymer matrix [1,2,3,4,5,6,7,8,9,10,11]. They can be considered solid analogies of magnetorheological fluids [12,13]. The related bulk properties are quite well-investigated, the physical processes behind the observed phenomena are not yet completely clarified and remain a subject of lively theoretical investigations; see, for example, References [7,10,28,29,30,31].
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