Cover Story: Shrinky-Dink Wrinkles

Wrinkles are bad, right? A sign of advancing age, a devil to try and get out of that smart shirt you need for your big important meeting, generally unsightly and always unwelcome... Not according to Michelle Khine and her co-workers at the University of California, who have been hard at work giving wrinkles a bit of a facelift. Sadly, this isn't a cure for ageing, so Advanced Materials can't claim to hold the secret of eternal youth just yet. However, I can at least indulge my inner child by enjoying the idea of creating nanostructures using children's toys called Shrinky-Dinks as a substrate (and yes, I'm grinning from ear to ear as I type...)

As a structural entity, wrinkles are potentially useful in a wide variety of applications such as flexible electronics, biological assays, sensor, optical devices, and actuators. For most of these applications, metal wrinkles are desirable, but previous processes for their manufacture have been painstaking and time-consuming, involving careful preparation and sometimes the use of expensive microfabricated molds or equipment (ion or electron beams). Using Shrinky-Dinks, which are essentially sheets of shape-memory polymer (pre-stressed polystyrene), Michelle and her team have come up with a quick, cheap and easy method of manufacturing nanoscale metal wrinkles. Even better, they can tune the wavelength and direction of the structures as desired. The process is simple: deposit a sheet of metal onto the polymer, and heat it at 160°C in the oven. The polymer sheet will shrink to about half its original size under these conditions, and because the metal is nonshrinkable, it buckles to cope with the strain, forming wrinkles. The wavelength of the wrinkles can be adjusted by varying the thickness of the metal layer, and specific directionality can be conferred or constrained by clamping the sheets along specific edges. Using gold as the metal layer produces structures that can be used for surface plasmon resonance and metal-enhanced fluorescence studies, which can be used in biomedical diagnostic devices, and combining the wrinkled structures with microfluidic systems inscribed into the polymer is a neat, quick way of producing lab-on-a-chip devices.

This is a great paper, harking back to my love of simple, elegant solutions. And while in this instance I can't take any particular credit for the cover design, the cover image was so stunningly eye-catching that I think 'glee' probably best sums up my initial reaction to it. The lower part of the image depicts some uniaxial gold nanowrinkles, and rolling down the axis are a series of cleverly designed insets showing different patterns that the technique has been used to create. The 3D rendering and lighting effect on the insets gives a dynamism to the whole image, and the colors are screaming for your attention. There's a faint biaxial patterning in the background, just before it fades out to black, giving a bit of depth. Choosing the color match for the title was all I had to do here, and I opted to keep it simple - there's enough going on in the main image to get you hooked - it doesn't need any help from me.

Lisa Wylie, Managing Editor
Advanced Materials
materialisam cover blog

C.-C. Fu et al., Adv. Mater. ; DOI: 10.1002/adma.200902294

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