Co-localised Raman and force spectroscopy reveal the roles of hydrogen bonds and π-π interactions in defining the mechanical properties of diphenylalanine nano- and micro-tubes

An integrated atomic force and polarized Raman microscope were used to measure the elastic properties of individual diphenylalanine (FF) nano- and micro-tubes and to obtain quantitative information regarding the inter-molecular interactions that define their mechanical properties. For individual tubes, co-localised force spectroscopy and Raman spectroscopy measurements allowed the calculation of the Young's and shear moduli (25 +/- 5 GPa and 0.28 +/- 0.05 GPa, respectively) and the contribution of hydrogen bonding network to the Young's modulus (similar to 17.6 GPa). The pi-pi interactions between the phenyl rings, dominated by T-type arrangements, were estimated based on previously published X-ray data to only 0.20 GPa. These results provide experimental evidence obtained from individual FF tubes that the network of H-bonds dominates the elastic properties of the FF tubes. (C) 2014 AIP Publishing LLC.