Shape Transition of Magnetic Field Sensitive Polymer Gels

Abstract

Magnetic field sensitive gels, called ferrogels, are chemically cross-linked polymer networks swollen by a ferrofluid. The monodomain magnetic particles, with a typical size of about 10 nm, couple the shape of the polymer gel to the nonuniform external magnetic field. Shape distortion occurs instantaneously and disappears abruptly when an external magnetic field is applied or removed, respectively. This work provides a thermodynamic analysis of shape transition based on the free energy of the swollen network that includes the elasticity of network chains as well as magnetic interactions of finely dispersed solid particles with the external field. It is shown that noncontinuous shape transition is due to a shift of equilibrium state from one local minimum to another one, similar to a first-order phase transition. The discussions presented here may be useful for the design of magnetically active soft polymeric actuators.

Magnetic and Mössbauer Studies of Magnetite-Loaded Polyvinyl Alcohol Hydrogels

“…Gel motions are driven and controlled by the magnetic field and the final shape is determined by a balance of magnetic and elastic interactions (10)(11)(12).…”

Microstructure and magnetic properties of magnetic fluids consisting of shifted dipole particles under the influence of an external magnetic field

“…All these features influence viscous, 7, 37-41 optical, 2-4, 42-44 diffusion, 6,45 scattering, [45][46][47][48][49][50][51][52] thermodynamic, 22 and acoustic 53 properties of ferrofluids. These systems are widely used in medicine, e.g., actuators [55][56][57] or sensors for the monitoring of anti-body reactions. 58 In the vast majority of ferrofluids, the nano-particles are spherical and the field they create can be approximated by that of a point dipole at the sphere's center.…”

β-cyclodextrin/poly(vinyl alcohol) hydrogels containing phenylpropionic acid and naphthylamine: dual pH-sensitive release

“…1 Many stimuli-sensitive hydrogels have been developed; they can adjust their swelling abilities and release their contents in response to temperature, 2 pH, 3 ionic strength, 4 inflammation, 5 glucose, 6 morphine, 7 antibodies, 8 metal, 9 urea, 10 an electric field, 11 a magnetic field 12 and ultrasonic radiation. 13 Among them, a pH-sensitive hydrogel is one of the most extensively studied for drug delivery systems.…”