Characterization of the actuator behavior of blended-system ferrogels

Abstract

Ferrogels are soft polymer materials containing a filler of magnetic particles that allow the material to be activated by magnetic fields. These materials have shown capabilities for large strains, fast response, ease of synthesis and biocompatibility and have potential applications including artificial muscles, controlled drug release systems, and hyperthermia cancer treatment. In this work the actuator behavior for a selection of ferrogel compositions and synthesis methods are characterized including their free strain and loading behavior. Samples were synthesized using either chemical or physical methods for samples containing PVA of 4, 8, and 12 wt% and magnetic particles of 1, 5, and 10 wt%. This samples were then tested for free strain and strain under loads of up to 4 times their weight by exposing them of fields from between 0.2 and 0.25T. Results show that softer samples with the largest amount of iron achieve the largest strains. Thus, chemically crosslinked sample with 4 wt% PVA and 10 wt% iron achieved the largest strain of almost 40%. Soft samples however exhibit low loaded capabilities with a blocked load of 1.7g identified. The physically crosslinked samples which were stiffer achieved very good loading capabilities with only a 20% strain decrease when loaded up to 400% of their weight. This translated in to a energy density of 320 J/m 3 making these materials very promising for actuator applications.

Axial strain of ferrogels under cyclic magnetic fields

“…These materials are magnetically activated smart materials with the capability to change their shape [1,2], water retention [3][4][5] and stiffness [6,7] when exposed to a magnetic field. Previous work by the authors [8] and others [2] has shown strains of up to 40% when exposed to fields of up to 2500 G. These materials are also related to magnetorheological elastomers which have shown strains of about 16% in uniform fields of 0.8 T [9] and tens to hundreds of per cent in nonuniform fields [10][11][12]. In addition, ferrogels have also shown load capabilities of up to four times the sample weight [8], translating into energy densities of about 400 J m −3 [13].…”

“…Previous work by the authors [8] and others [2] has shown strains of up to 40% when exposed to fields of up to 2500 G. These materials are also related to magnetorheological elastomers which have shown strains of about 16% in uniform fields of 0.8 T [9] and tens to hundreds of per cent in nonuniform fields [10][11][12]. In addition, ferrogels have also shown load capabilities of up to four times the sample weight [8], translating into energy densities of about 400 J m −3 [13]. Such observations suggest ferrogels for actuator behavior; however, before target applications can be chosen and actuators designed, the dynamic behavior of these materials needs to be better understood.…”

Effect of cross-linker and dopant concentrations on the magnetic properties of poly(vinyl alcohol)-borax ferrogels

“…Various research groups have synthesized and studied PVA-borax ferrogels with micron-sized carbonyl iron particles as the magnetic ller. In one such study, Park et al have found such chemically cross-linked matrices to possess lower stiffness and greater ability for mechanical strains when compared to physically cross-linked ones [11]. The mechanical strains in such ferrogels are related to their exibility and to the concentration of the dopant particles [12].…”

Development of a continuum model for ferrogels

“…Ferrogels are often characterized by their low stiffness (below 10 kPa), large deformation of up to 40%, and high water absorption (Faidley et al, 2010; Han et al, 2011; Park et al, 2008; Raikher and Stolbov, 2003, 2005; Zrínyi et al, 1997). Owing to their unique properties, ferrogels are suitable for a variety of mechanical (An and Shaw, 2003; Kato et al, 1997; Meng and Hu, 2010; Mitwalli et al, 1997; Monz et al, 2008; Zimmermann et al, 2011, 2006; Zrínyi et al, 1998) and medical (Chan et al, 2013; Lao and Ramanujan, 2004; Liu et al, 2008, 2006; Qin et al, 2009; Satarkar and Hilt, 2008; Thévenot et al, 2013) applications.…”