Graphene multilayer as nanosized optical strain gauge for polymer surface relief gratings.

In this paper, we show how graphene can be utilized as a nanoscopic probe in order to characterize local opto-mechanical forces generated within photosensitive azobenzene containing polymer films. Upon irradiation with light interference patterns, photosensitive films deform according to the spatial intensity variation, leading to the formation of periodic topographies such as surface relief gratings (SRG). The mechanical driving forces inscribing a pattern into the films are supposedly fairly large, because the deformation takes place without photofluidization; the polymer is in a glassy state throughout. However, until now there has been no attempt to characterize these forces by any means. The challenge here is that the forces vary locally on a nanometer scale. Here, we propose to use Raman analysis of the stretching of the graphene layer adsorbed on top of polymer film under deformation in order to probe the strength of the material transport spatially resolved. With the well-known mechanical properties of graphene, we can obtain lower bounds on the forces acting within the film. Upon the basis of our experimental results, we can deduce that the internal pressure in the film due to grating formation can exceed 1 GPa. The graphene-based nanoscopic gauge opens new possibilities to characterize opto-mechanical forces generated within photosensitive polymer films.

Monitoring the dispersion process of SWNTs in aqueous solutions by UV-vis and Raman spectroscopies.

The current bottleneck to carbon nanotubes (CNT) application in composite materials field consists in the difficulty of dispersing them in solvents. As a result of strong van der Waals interactions, as produced CNTs are tightly bundled in ropes of several tubes, rendering the carbon-powder insoluble in aqueous and organic liquids and thus unprocessable. The interest in applications that require water-soluble CNTs is growing and much attention is being directed to the study of surfactant aqueous solutions. In a typical dispersion procedure, after the surfactant has been adsorbed on the nanotube surface by hydrophobic or pi-pi interactions, ultrasonication helps nanotubes debundling, providing a mechanical energy able to overcome van der Waals interactions in CNT bundles. The electrostatic repulsion between surfactant polar heads that remain in solution allows the colloidal stability. In this work the dispersibility of HiPCO Single Walled Carbon Nanotubes (SWNT) in different surfactant solutions has been evaluated by using UV-vis and Raman spectroscopies. UV absorbance as well as intensity of SWNTs characteristic Raman bands have been studied as a function of sonication time for each type of surfactant. Moreover the surface morphology of SWNTs films obtained by solutions drying has been observed by using Scanning Electron and Atomic Force Microscopies.