Button shows "Canyons in the Nanocosmos"

For the first time, a new process identifies surface structures, including soft plastics

Form and arrangement of crystalline fins beneath the surface of elastomeric polypropylene. © TU Chemnitz
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Physicists have used a supposed disadvantage of atomic force microscopy for a new process: they used the slight penetration of the probe tip to scan and imitate the structures of soft plastics hidden just below the surface. With the new non-destructive measuring method, the surface structure of even soft materials can be determined more precisely for the first time.

In order to map soft surfaces of plastics, liquids or living cells, researchers worldwide use atomic force microscopy in touch mode. The shape of the surface is scanned line by line with a very fine, vibrating tip, which sometimes penetrates a few nanometers deep into the soft surface. This low penetration of the tip was previously considered as an undesirable side effect of this measurement method and the representation of the surface was possible only as an area.

Vibrating tip feels structure under the surface

However, a research team led by Eike-Christian Spitzner, Christian Riesch and Professor Robert Magerle of the Chemnitz University of Technology has now used the supposed disadvantage of penetrating the tip to spatially sample and display the near-surface layers of soft plastics for the first time.

The measuring method developed by the physicists works in a similar way as the palpation of a hand's back: the vibrating tip touches the surface like a finger touches the surface of the hand. With a little more pressure, the soft tissue under the skin gives way and with the finger hard and soft spots under the surface can be felt. When the finger is withdrawn, the tissue of the back of the hand returns to its original shape. Even the tip of the atomic force microscope can easily penetrate to the surface of the soft plastic to a certain point, without permanently deforming them.

Gum as a canyon landscape in the nanocosmos

With this new measurement method, the researchers from Chemnitz have investigated, among other things, elastomeric polypropylene (a synthetic rubber) and, under its surface, the form only 15 displays

Nanometer wide crystalline lamellae, which looks like a canyon landscape in the nanocosmos. The width of the "ridges" is about 2, 000 times smaller than the diameter of a human hair.

Physicists were able to show that the surface of the plastic is completely smooth and the hard, crystalline fins are five to fifteen nanometers below a soft layer of amorphous polypropylene. The upper edge of the lamellae is not smooth, but joints could be felt between the approximately 20 nanometer-sized crystalline blocks, which - to stay in comparison with the Handr cken - correspond to the Kn cheln.

The new measuring method is non-destructive and can be used in many ways for the analysis of plastic surfaces. It promises new insights below the surface of soft materials that are crucial to understanding their surface properties such as adhesion and friction. (ACS Nano, 2010 DIO: http://dx.doi.org/10.1021/nn1027278)

(Technische UniversitĆ t Chemnitz, 03.01.2011 - NPO)