While shape-memory materials do have some interesting potential applications, many of them require the application of heat in order to change shape – and that could cause problems, in temperature-sensitive environments such as the human body. A new material, however, relies instead on a magnetically-responsive liquid.
Developed by scientists at Switzerland's Paul Scherrer Institute and ETH Zurich, the substance consists of a silicone-based polymer with liquid droplets encapsulated within it. That "magnetorheological liquid" is in turn made up of water, glycerine and tiny particles of carbonyl iron – the liquid's composition is similar to that of milk, in which fat droplets are dispersed within an aqueous solution.
When not being exposed to a magnetic field, the material remains soft and flexible. Once such a field is applied, though, the droplets become elongated, and the iron particles align themselves along the magnetic field lines. These two factors cause an almost 30-fold increase in the material's stiffness.
In practise, this means that if the soft material is manually formed into a certain shape and then subjected to a magnetic field, it becomes rigid and holds that shape until the field is removed. When the latter happens, the material reverts to its original shape, and to its soft state.
Previous studies have produced magnetically-activated shape-memory materials made up of polymers with metal particles embedded inside of them. According to the Swiss researchers, however, the fluid nature of the magnetorheological liquid allows their polymer to become much stiffer.
Possible applications for the new material include catheters that change stiffness after being safely and easily inserted through blood vessels, self-deploying tires on rover vehicles used to explore other planets, or robotics components that can perform movements without the need for a motor.
A paper on the material – which is demonstrated in the video below – was recently published in the journal Advanced Materials.
Source: Paul Scherrer Institute
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