A range of analytical techniques (DSC, conductivity measurement, Raman spectroscopy, small- and wide-angle X-ray diffraction (S-WAXS), quasi-elastic neutron scattering (QENS), and single-crystal X-ray diffraction) are applied to the characterization of the phase behavior of the low-melting-point liquid crystalline salts 1-hexadecyl-3-methylimidazolium hexafluorophosphate ([C16mim][PF6]) and 1-methyl-3-tetradecylimidazolium hexafluorophosphate [C14mim][PF6]. This is the first time that QENS has been applied to the structural analysis of this type of ionic liquid crystal. For the first time in this class of salts, a low-temperature phase transition is identified, which is assigned to a crystal-crystal transition. Conductivity and QENS data for [C16mim][PF6] suggest that the higher-temperature crystalline phase (CII) has greatly increased freedom in its long alkyl chain and anion than the lowertemperature crystalline phase (CI). This conclusion is supported by single-crystal X-ray diffraction results for [C14mim][PF6]. In both crystalline phases, as well as in the highertemperature mesophase, the structure maintains a monodispersed layer structure with interdigitated alkyl chains. The structure of the mesophase is confirmed as smectic A by the S-WAXS and Raman spectroscopy results. Detailed analysis suggests that in this phase the alkyl chains undergo complete conformational melting. Introduction Ionic liquid (IL) is the term now widely applied to salts that are liquid at or below 100 °C. ILs show great promise as environmentally benign reaction media for many types of chemical processes.1 The key to sustainable technology is achieving an economic benefit with environmental improvements: the use of ILs offers improved performances and greater flexibility for a variety of processes such as biphasic catalysis and organic synthesis,2 separations,3 electrochemistry,4 photochemistry, 5 and liquid crystals,6 potentially leading to economic advantages. ILs are also environmentall

This work defines and examines four classes of magnetorheological elastomers (MREs) based upon permutations of particle alignment-magnetization pairs. Particle alignments may either be unaligned (e.g. random) or aligned. Particle magnetizations may either be soft-magnetic or hard-magnetic. Together, these designations yield four material types: A-S, U-S, A-H, and U-H. Traditional MREs comprise only the A-S and U-S classes. Samples made from 325-mesh iron and 40 μm barium hexaferrite powders cured with or without the presence of a magnetic field served as proxies for the four classes. Cantilever bending actuating tests measuring the magnetically-induced restoring force at the cantilever tip on 50 mm × 20 mm × 5 mm samples yielded ∼350 mN at μ 0 H = 0.09 T for classes A-H, A-S, and U-S while class U-H showed only ∼40 mN. Furthermore, while classes U-S and A-S exerted forces proportional to tip deflection, they exerted no force in the undeformed state whereas class A-H exerted a relatively constant tip force over its entire range of deformation. Beam theory calculations and models with elastic strain energy density coupled with demagnetizing effects in the magnetic energy density were used to ascertain the magnitude of the internal bending moment in the cantilever and to predict material response with good results. This work highlights the ability of the newly developed A-H MRE materials, and only that material class, to operate as remotely powered bidirectional actuators.

This work seeks to provide a framework for the numerical simulation of magneto-active elastomer (MAE) composite structures for use in origami engineering applications. The emerging field of origami engineering employs folding techniques, an array of crease patterns traditionally on a single flat sheet of paper, to produce structures and devices that perform useful engineering operations. Effective means of numerical simulation offer an efficient way to optimize the crease patterns while coupling to the performance and behavior of the active material. The MAE materials used herein are comprised of nominally 30% v/v, 325 mesh barium hexafarrite particles embedded in Dow HS II silicone elastomer compound. These particulate composites are cured in a magnetic field to produce magneto-elastic solids with anisotropic magnetization, e.g. they have a preferred magnetic axis parallel to the curing axis. The deformed shape and/or blocked force characteristics of these MAEs are examined in three geometries: a monolithic cantilever as well as two- and four-segment composite accordion structures. In the accordion structures, patches of MAE material are bonded to a Gelest OE41 unfilled silicone elastomer substrate. Two methods of simulation, one using the Maxwell stress tensor applied as a traction boundary condition and another employing a minimum energy kinematic (MEK) model, are investigated. Both methods capture actuation due to magnetic torque mechanisms that dominate MAE behavior. Comparison with experimental data show good agreement with only a single adjustable parameter, either an effective constant magnetization of the MAE material in the finite element models (at small and moderate deformations) or an effective modulus in the minimum energy model. The four-segment finite element model was prone to numerical locking at large deformation. The effective magnetization and modulus values required are a fraction of the actual experimentally measured values which suggests a reduction in the amount of magnetic torque transferred from the particles to the matrix.

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This work uses dynamic shearing experiments to examine S- (soft magnetic) and H- (hard magnetic) magnetoactive elastomers of four different types. The aligned materials had larger shear stiffness, and all materials but the unaligned H material displayed increased stiffness with magnetic field. All four types showed generally the same damping ratio with no strong trends across material types. We discuss these results in terms of shearing forces arising due to magnetic torques.