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Morphable Surfaces Reduce Air Resistance

A morphable surface developed by an MIT team can change surface texture — from smooth to dimpled, and back again — through changes in pressure. When the inside pressure is reduced, the flexible material shrinks, and the stiffer outer layer wrinkles. Increasing pressure returns the surface to a smooth state.

Adding golf ball-like dimples to surfaces could reduce drag and improve efficiency of vehicles.

The ability to change the surface in real time comes from the use of a multilayer material with a stiff skin and a soft interior — the same basic configuration that causes smooth plums to dry into wrinkly prunes. To mimic that process, the team made a hollow ball of soft material with a stiff skin — with both layers made of rubberlike materials — then extracted air from the hollow interior to make the ball shrink and its surface wrinkle.

Because the surface texture can be controlled by adjusting the balls’ interior pressure, the degree of drag reduction can be controlled at will. “We can generate that surface topography, or erase it,” said MIT’s Pedro Reis. “That reversibility is why this is pretty interesting; you can switch the drag-reducing effect on and off, and tune it.”

Many researchers have studied various kinds of wrinkled surfaces, with possible applications in areas such as adhesion, or even unusual optical properties.

“But we are the first to use wrinkling for aerodynamic properties,” said Reis.

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