An image of the ‘fruitcake’ structure of the semiconducting polymer, showing the ordered and disordered regions, produced by higher-eigen-mode imaging. Image: University of Cambridge.
An image of the ‘fruitcake’ structure of the semiconducting polymer, showing the ordered and disordered regions, produced by higher-eigen-mode imaging. Image: University of Cambridge.

Researchers have analyzed the properties of an organic polymer with potential applications in flexible electronics and uncovered variations in its hardness at the nanoscale, the first time such a fine structure has been observed in this type of material.

The field of organic electronics has benefited from the discovery of new semiconducting polymers with molecular backbones that are resilient to twists and bends, allowing them to transport charge even if they are flexed into different shapes.

It had been assumed that these materials resemble a plate of spaghetti at the molecular scale, without any long-range order. However, an international team of researchers has now found that, for at least one such material, there are tiny pockets of order within. These ordered pockets, just a few ten-billionths of a meter across, are stiffer than the rest of the material, giving it a ‘fruitcake’ structure with harder and softer regions.

The work was led by researchers at the University of Cambridge and Park Systems UK Limited, both in the UK, together with colleagues at KTH Stockholm in Sweden, the Universities of Namur and Mons in Belgium, and Wake Forest University. Their results, reported in a paper in Nature Communications, could be used to help develop next-generation microelectronic and bioelectronic devices.

Studying and understanding the mechanical properties of these materials at the nanoscale – a field known as nanomechanics – could help scientists fine-tune those properties and make the materials suitable for a wider range of applications.

“We know that the fabric of nature on the nanoscale isn’t uniform, but finding uniformity and order where we didn’t expect to see it was a surprise,” said Deepak Venkateshvaran from Cambridge’s Cavendish Laboratory, who led the research.

The researchers used an imaging technique called higher-eigen-mode imaging to take nanoscale pictures of the regions of order within a semiconducting polymer called indacenodithiophene-co-benzothiadiazole (C16-IDTBT). These pictures showed clearly how individual polymer chains line up next to each other in some regions of the polymer film. These regions of order are 10–20nm across.

“The sensitivity of these detection methods allowed us to map out the self-organization of polymers down to the individual molecular strands,” said co-author Leszek Spalek, also from the Cavendish Laboratory. “Higher-eigen-mode imaging is a valuable method for characterizing nanomechanical properties of materials, given the relatively easy sample preparation that is required.”

Further measurements of the stiffness of the material on the nanoscale showed that the areas where the polymers self-organized into ordered regions were harder, while the disordered regions of the material were softer. These experiments were performed under ambient conditions rather than an ultra-high vacuum, which had been a requirement in earlier studies.

“Organic polymers are normally studied for their applications in large area, centimeter-scale, flexible electronics,” said Venkateshvaran. “Nanomechanics can augment these studies by developing an understanding of their mechanical properties at ultra-small scales with unprecedented resolutions.

“Together, the fundamental knowledge gained from both types of studies could inspire a new generation of soft microelectronic and bioelectronic devices. These futuristic devices will combine the benefits of centimeter-scale flexibility, micrometer-scale homogeneity, and nanometer-scale electrically controlled mechanical motion of polymer chains with superior biocompatibility.”

This story is adapted from material from the University of Cambridge, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.