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Controlled wrinkling

 

Images taken with a 3D microscope show wrinkled surfaces produced using a method developed by the MIT team. The size, spacing and angles of the wrinkles vary depending on how much the original underlying surface was stretched, and how the stretching was released Credit: Jose Luis Yague and Felice Frankel

 


By stretching and releasing material in a controlled and orderly way, researchers from Massachusetts Institute of Technology (MIT) have discovered a way of making perfectly ordered and repeatable wrinkled surfaces.


The MIT researchers have developed a method to precisely control the size and pattern of wrinkles using polymeric material at the microscopic level. Their method uses two layers – a silicon-based polymer substrate layer that can be stretched, and a second layer of polymeric material which is deposited through an initiated chemical vapour deposition (iCVD) process.

 


The stretching is released first in one direction, and then in the other – rather than all at once. This controlled, stepwise release creates a perfectly ordered herringbone or zigzag pattern, the size and spacing of which is determined by how much the underlying material was originally stretched in each direction, the coating thickness and in which order the two directions are released.

 


“One distinguishing feature of what we’re showing is the ability to create deterministic two-dimensional patterns of wrinkles,” said Professor Mary Boyce. “The deterministic nature of these patterns is very powerful and yields principles for designing desired surface topologies.”

 


The predictability of the resulting patterns was a big surprise say the MIT team, who have published their results in Advanced Materials.

 


“One of the amazing things is to note how beautifully the experiments and the simulations match,” said Professor Karen Gleeson.

 


Most techniques have been used to create surfaces with tiny patterns, whose dimensions can range from nanometres to tens of micrometres – most however require complex fabrication and can only be used for very tiny areas. The new method is both very simple – consisting of just two or three steps – and can be used to make patterned surfaces of larger sizes.

 


The researchers say the method could be used to create a wide variety of useful structures including microfluidic systems for biological research, sensing and diagnostics; new photonic devices that can control light waves; controllable adhesive surfaces and antireflective coatings.