A team at Brown University in Rhode Island led by Po-Yen Chen set out to determine whether introducing complex architectural structures, including crumples and wrinkles, into graphene could enhance its electrochemical and other properties.

Wrinkles in graphene enhance some of its properties. Image source: Hurt and Wong Labs/Brown University.They had already learned that adding wrinkles in a multi-step process gave graphene the ability to shed water, potentially useful in self-cleaning applications. The latest twist on the work deposited layers of graphene on polymer membranes. When the polymer is heated it shrinks, causing the graphene to wrinkle and crumple.

Using various techniques to control the direction of the shrinkage yielded differing results. When the team clamped opposite ends, the graphene exhibited generally periodic, parallel wrinkles. Unclamped polymer, meanwhile, yielded graphene that was crumpled in random shapes. Rotating the film using clamped versus unclamped polymer and reshrinking the same sheet over a series of successive melts offered varying results, even showing wrinkles and crumples superimposed upon each other. Ultimately the multi-generational approach led the team to a compressed sheet as small as one-fortieth its original size.

“As you go deeper into the generations you tend to get larger wavelength structures with the original, smaller wavelength structure from earlier generations built into them,” said Robert Hurt, a professor of engineering at Brown.

The variety of crumpling techniques result in different mechanical properties: with as few as three unclamped shrinks, the material becomes superhydrophobic. Crumpled graphene exhibits as much as a 400% increase in electrochemical current density as compared to flat graphene sheets. The team is looking to tweak the process to determine if they can create stretchable electronics, and if the process itself could be used with other nanomaterials.