Magneto-Mechanical Actuators with Reversible Stretching and Torsional Actuation Capabilities
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.123
Magneto-Mechanical Actuators with Reversible Stretching and Torsional Actuation Capabilities M. Yasar Razzaqa, M. Behla, A. Lendleina,b a
Institute of Biomaterial Science, Helmholtz-Zentrum Geesthacht, Kantstr. 55, 14513 Teltow, Germany Institute of Chemistry, University of Potsdam, 14476 Potsdam, Germany
b
ABSTRACT
Composite actuators consisting of magnetic nanoparticles dispersed in a crystallizable multiphase polymer system can be remotely controlled by alternating magnetic fields (AMF). These actuators contain spatially segregated crystalline domains with chemically different compositions. Here, the crystalline domain associated to low melting transition range is responsible for actuation while the crystalline domain associated to the higher melting transition range determines the geometry of the shape change. This paper reports magnetomechanical actuators which are based on a single crystalline domain of oligo(ωpentadecalactone) (OPDL) along with covalently integrated iron(III) oxide nanoparticles (ioNPs). Different geometrical modes of actuation such as a reversible change in length or twisting were implemented by a magneto-mechanical programming procedure. For an individual actuation mode, the degree of actuation could be tailored by variation of the magnetic field strengths. This material design can be easily extended to other composites containing other magnetic nanoparticles, e.g. with a high magnetic susceptibility.
INTRODUCTION Magneto-mechanical actuators are relevant for artificial muscles and their applications for humanoid robots, smart fabrics and exoskeletons [1-12]. Alternating magnetic field (AMF) provides remote heating of magnetic particles in a nanocomposite by hysteresis or relaxational mechanisms [6, 7, 13-18]. This remote heating is useful to initiate the actuation of thermo-sensitive polymer nanocomposites e.g., smart hydrogels, ferrogels, liquid crystalline elastomers (LCE) [6, 19]. Remote controlled contraction/expansion of magnetic nanocomposites of poly(n-isopropylacrylamide) (PNIPAAm) for drug release and microfluidic applications has been reported [20]. Incorporation of iron(III) oxide nanoparticles (iONP) in LCE enabled a reversible change in length which was remotely controlled by AMF [1]. Recently, magnetic actuators based on crystallizable polymer nanocomposites with chemically heterogeneous structure were reported [14]. The nanocomposite consisted of two separate crystallizable structural units
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with distinct melting (Tm) and crystallization temperatures (Tc) along with covalently integrated ioNPs. Thermo-mechanical programming of these nanocomposites resulted in an oriented actuating domain (AD) (with lower Tm), which maintained its orientation, while undergoing
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