Nanoparticle-Based Magnetorheological Elastomers with Enhanced Mechanical Deflection for Haptic Displays

Abstract

Haptics allows tactile interactions between humans and digital interfaces. Magnetorheological elastomers (MREs) constitute a promising candidate material for creating the tactile interface of the futureone able to recreate 3D shapes that can be sensed with touch. Furthermore, an MRE formed by using nanoparticles, as opposed to previously used microparticles, is necessary to generate a variety of shapes involving sharp curvatures over small, micrometer-scale horizontal distances to pave the way for haptic displays with microtexture resolution. Here we fabricated both isotropic and anisotropic MREs with different concentrations (2–8 vol % nanoparticles) of soft, low-remanence ferromagnetic nanoparticles. When placed in a magnetic field gradient, isotropic MREs, nonintuitively, show higher deflection than anisotropic MREs, with the former achieving displacement on the order of a millimeter at just 100 mT. This enhanced performance in the isotropic case is explained based on the soft magnetic nature of the nanoparticles. We show that performance improves with magnetic content up to a composition of 6 vol %, where it plateaus. This behavior is attributed to the stiffness of the composite material increasing at a faster rate than the magnetization as the rigid magnetic nanoparticles are added to the elastomeric matrix. Moreover, 6 vol % microparticle-based isotropic and anisotropic MREs were fabricated and compared with the nanoparticle-based MREs. Anisotropic nanoparticle-based films show higher deflection when compared with their microparticle-based counterparts. The latter is only able to match the nanoparticle film deflection at higher applied fields of almost 300 mT. This performance difference between nanoparticle and microparticle-based films is attributed to the increased anisotropic film stiffness resulting from the larger micrometer-size particles. Finally, the optimally designed nanoparticle-based isotropic film was utilized to create a programmable and real-time reconfigurable braille-inspired interface.

Enhanced Magnetic Anisotropy for Reprogrammable High‐Force‐Density Microactuators

“…As implied by the previous results, the optimal magnetic filler concentration for a soft magnetic actuator was found to be 6 vol%, which gave the highest anisotropy and remanent magnetization, while also yielding the lowest element-to-element interaction. To further verify this finding, we experimentally studied the deformations of the anisotropic magnetic films prepared with different volume fractions (2,4,6,8, and 10 vol%) of magnetic nanochains in the varying magnetic field. The fabrication process of anisotropic magnetic elastomers can be found in the Experimental Section.…”

“…Magnetic actuation is flourishing as the preferred mode of actuation in a number of new devices and technological systems, including soft robots, [1,2] tactile displays, [3,4] mechanical metamaterials, [5,6] and minimally invasive medical devices. [7,8] The advantage of magnetic actuation arises from the fast response time to external magnetic fields and the large design space for magnetic programming of the actuation behavior.…”

Development of a Soft Actuator from Fast Swelling Macroporous PNIPAM Gels for Smart Braille Device Applications in Haptic Technology

“…The key challenge of such a tactile surface relies on the complexity to actuate a high number of pins independently. , It would require low-cost millimeter actuating systems. Several strategies have been explored based not only on piezoelectric systems but also on pneumatic actuation, , magnetic actuation, − or others. − Today none of these strategies have reached a commercialized status.…”

A unified understanding of magnetorheological elastomers for rapid and extreme stiffness tuning

“…Magnetic elastomer composites have traditionally been created by incorporating magnetic particles into soft elastomers such as silicones or polyurethanes, 25 to provide a combination of soft mechanical response and magnetic functionality for applications including stretchable and adaptive electronics and sensing, [26][27][28][29][30][31] automotive components, [32][33][34] and soft robotic grippers. [35][36][37][38][39] A key feature that has lead to substantial research of MREs is their magnetorheological effect, which leads to magnetic field-driven tunable stiffness, 17,18 variable energy dissipation and damping, 40,41 and shape-memory effects.…”

“…[35][36][37][38][39] A key feature that has lead to substantial research of MREs is their magnetorheological effect, which leads to magnetic field-driven tunable stiffness, 17,18 variable energy dissipation and damping, 40,41 and shape-memory effects. 42 To improve the stiffness tuning effect (often called the MR effect or MR ratio) of these materials, MREs have been created with varied parameters such as elastomer matrix material, [43][44][45][46][47][48][49][50] magnetic particle size, 28,43,48,51 shape, [52][53][54] and volume fraction, 44,[55][56][57] and recently through the introduction of magnetic fluids as functional content. 29,42,58 Magnetorheological fluids, which are magnetic fluids that rapidly change viscosity and yield stress when subjected to a magnetic field, 59,60 have recently been used as inclusions for MREs.…”