US scientists develop shape-memory rubber

ERJ staff report (DS)

Rochester, New York -- Scientists at the University of Rochester in New York have developed a shape-memory rubber. The material, described in the journal Advanced Materials, forms a new class of shape-memory polymers, which are materials that can be stretched to a new shape and will stay in that form until heated, at which time they revert to their initial shape.

Unlike conventional shape-memory polymers, however, the new material is transparent, rubbery, and most importantly, engineers will be able to control the speed at which it returns to its original shape. Other shape memory polymers use crystallisation to hold a temporary shape, which often makes them opaque, hard, and brittle in their frozen states, and this can limit their use.

"At higher temperatures the material stretches like a rubber band, but, at lower temperatures, it stiffens up," says Mitchell Anthamatten, assistant professor of chemical engineering and inventor of the material. "This property can be used to temporarily hold the material in a deformed shape; and its original shape can be recalled by heating. Imagine an optical lens that can be triggered to change shape, a face-mask that can fit any user, or a biomedical implant that changes shape slow enough for a surgical procedure."

One aspect of the clear rubber that surprised Anthamatten was how easy it is to make. "It's ridiculously simple," he says, "and we're fascinated by how small modifications lead to major changes in how the material behaves."

The new rubber functions differently than conventional shape-memory materials by using "sticker groups"-hydrogen bonding groups that form temporary bonds. These sticker groups break and reform constantly. It's akin to tearing a net apart only to find that new knots have formed between different strands. When the material is stretched, new bonds form that hold the material, temporarily, in its deformed shape. Creating the rubber with different amounts of sticker groups controls the rate at which the rubber returns to its original shape. With this control, Anthamatten envisions applications that today's shape-memory polymers simply can't fulfill.

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Press release from University of Rochester