Tensile elastic modulus of free-standing single-layer and bilayer polymer films*

Studies have shown that the elastic modulus, E, of polymer films may vary with the film thickness, h, when h is tens of nanometers. For polystyrene (PS) supported by a polydimethylsiloxane (PDMS) substrate, E had been found to decrease with decreasing h below ~60 nm. For free-standing PS films, however, E was found to be constant with h for h < ~80 nm. In this experiment, we conducted uniaxial tensile tests on free-standing PS films (with a molecular weight, MW, of 1,049 kg/mol and h = 40 to 150 nm) and bilayer films of PS-PDMS (with various MW from 151 to 1,049 kg/mol and h = 12 to 150 nm). The measured elastic modulus of the films agreed with published value of bulk PS, showing insignificant dependences on h or MW.