Elastic moduli, E, of free-standing polystyrene (PS) single-layers and polystyrene–polydimethylsiloxane (PS-PDMS) bilayers are measured by uniaxial tensile testing at room temperature under different strain rates, γ̇, and for PS thicknesses, h, from 8 to 130 nm. As γ̇ increases, E increases initially, then approaches the bulk value, E bulk, when γ̇ exceeds a characteristic value (≡ τ–1) that decreases with increasing h. The noted variation of E with γ̇ shows that stress relaxation occurs in the films during measurement when γ̇τ ≪ 1, while the noted variation of τ–1 with h shows that thinner films relax faster. Consequently, E decreases with decreasing h if γ̇ is small, but displays independence of h if γ̇ is large. Visually, the crossover takes place at around γ̇ = 0.0015 s–1, where at γ̇τ > 1 for all films.

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The bending-induced micro-crack leads to the incomplete rupture of the conducting filaments and reduces the local depletion-region width.