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.

中文翻译：

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自立式聚合物纳米薄膜弹性模量的应变率和厚度依赖性

独立式聚苯乙烯 (PS) 单层和聚苯乙烯-聚二甲基硅氧烷 (PS-PDMS) 双层的弹性模量E是通过室温下不同应变率 γ̇ 和 PS 厚度h的单轴拉伸试验测量的，从8 至 130 纳米。随着 γ̇ 增加，E最初增加，然后在 γ̇ 超过随h增加而减小的特征值 (≡ τ ^–1 ) 时接近体积值E _bulk。E随 γ̇的显着变化表明，当 γ̇τ ≪ 1 时，薄膜中发生应力松弛，而 τ ^–1随h的显着变化表明较薄的薄膜松弛得更快。因此，如果 γ̇ 小，则E随着h的减小而减小，但如果 γ̇ 大，则显示h的独立性。从视觉上看，交叉发生在 γ̇ = 0.0015 s ^–1左右，其中所有电影的 γ̇τ > 1。