Nanomechanical properties of poly(l-lactide) nanofibers after deformation

Atomic force microscopy (AFM) technique was used to investigate the nanomechanical properties of poly(l-lactide) (PLLA) nanofibers produced by the thermally induced phase separation (TIPS) method. Firstly, AFM-based nanolithography was employed to produce localized deformations on the surface of single PLLA nanofiber, in which the AFM tip served as a nanoscale burin to draw a scratch longitudinally along the nanofiber. Secondly, the morphology and physical properties of the nanofiber before and immediately after the deformation were characterized with AFM and force spectroscopy measurement. During the initial stage of TIPS process, the crystallization of PLLA resulted in a regular arrangement of crystalline domains along the thinner fibrils which then assembled laterally into larger nanofibers. The deformation due to the nanoindentation and plowing with the probe induced structural variation of PLLA nanofibers and led to a functional consequence in their nanomechanical properties. The region after deformation had a higher adhesion force and elastic modulus, probably because the polymer chains became more compact and ordered under both compression and shear stresses.