Advanced Functional Materials

Cover image for Vol. 25 Issue 10

17_07/2007Cover Picture: A Route to Self-Organized Honeycomb Microstructured Polystyrene Films and Their Chemical Characterization by ToF-SIMS Imaging (Adv. Funct. Mater. 7/2007)

The cover shows a composition of different characterization images of an auto-organized polystyrene film obtained through breath-figure imprinting, as reported by Sami Yunus and co-workers on p. 1079. Water-droplet condensation, represented as a synthetic perspective image (top), is responsible for ordered microstructuring during film formation. The following perspectives are taken from SEM and from three negative ToF-SIMS images that allow deduction of the surface chemical composition. The background is an SEM picture of a polydimethylsiloxane molding of the self-organized film.

A new type of polymer compound that allows the formation of highly ordered microstructured films by casting from a volatile solvent in the presence of humidity, and its characterization by ToF-SIMS (time-of-flight secondary-ion mass spectrometry) are presented. A honeycomb structure is obtained by activation of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO)-terminated polystyrene (PS) with p-toluenesulfonic acid (PTSA). The mechanism of this activation reaction, leading to a more polar PS termination, is deduced from simple experiments and supported by ToF-SIMS characterization. Positive and negative ToF-SIMS imaging allows different chemical regions correlating to the film morphology to be distinguished. This new, straightforward activation process, together with ToF-SIMS chemical imaging, provides a better understanding of the phenomena underlying the formation of these films by directly linking the role of polar terminations to the microscale self-organization. This new method, transposable to other organic acids, suggests interesting new perspectives in the field of self-organized chemical and topographical patterning.

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