Nanowear of Polymers
Authors: D’Acunto M., Dinelli F., Pingue P.
Autors Affiliation: Istituto di Struttura della Materia, ISM-CNR, via Fosso del Cavaliere, 100, 00133 Rome, Italy
Istituto Nazionale di Ottica, INO-CNR, via Moruzzi 1, 56124 Pisa, Italy
NEST, Scuola Normale Superiore and Istituto Nanoscienze – CNR, Piazza San Silvestro 12, 56127 Pisa, Italy
Abstract: The use of viscoelastic materials, such as polymers, constantly increases in the field of nanotechnology. These materials are softer than metallic and inorganic ones, and, because of that, they are easier to deform and wear off. The wear mechanisms occurring for viscoelastic materials are rather complex, and, generally, present more complications for a direct investigation with respect to metals or ceramics materials. With the advent of Scanning Probe Microscopy (SPM), well characterized forces can be applied to a surface with a nanometer-scale spatial resolution. In particular Atomic Force Microscopy (AFM), working at high contact forces, can significantly modify many surfaces. Polymers are soft enough to be modified by hard AFM tips, such as those of silicon, silicon nitride or diamond. For these reasons, the AFM is today the main tool employed to investigate wear occurrence on polymer surfaces. The wear of a polymer surface caused by an AFM tip in a regime of single asperity contact is an articulate process that depends on conditions such as, namely, the applied forces, the tip shape, size and the relative velocity. Since the influence of all these parameters is in close connection with the sample properties, one can expect a dependence of the wearing process on the mechanical properties of the sample surfaces. These properties can vary significantly from the bulk properties, if cross linking is made or, on contrary, residual solvents are present in the specimens. This chapter is divided in three sections following a general introduction. Specifically, the first section deals with wear induced by means of AFM tips to study the mechanical properties of films at the nanoscale; the second one regards the exploitation of wear for the creation of nanolithographic patterns; the last one is finally dedicated to an applicative field such as the characterization of wear of polymers for biomedical applications at the meso- and nanoscales.
KeyWords: Polymers; Nanowear; Viscoelasticity; Friction; SPM