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The Elastic Mechanical Response of Nanoscale Thin Films of Miscible Polymer/Polymer Blends

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journal contribution
posted on 2015-06-23, 00:00 authored by Peter C. Chung, Peter F. Green
Nanoindentation measurements of the elastic moduli Er of thin polymer films supported by stiff substrates with moduli EsEr show an increase of Er with decreasing h, for h less than a threshold thickness ht. In the thickness range h < ht , the value of the modulus manifests the influence of various interactions associated with the “stiff” substrate. We show that ht is a function of composition for the miscible blend of polystyrene (PS) and tetramethyl bisphenol-A polycarbonate (TMPC). The modulus Er,TMPC of TMPC films supported by SiOx increases for h < ht(TMPC) ∼ 300 nm while ht(PS) ∼ 450 nm for the modulus Er,PS of PS films, supported by the same substrate. The threshold thicknesses of the blends and the moduli of the blends appear to be reasonably described by an effective medium approximation. This behavior is rationalized in terms of the vibrational force constants f, determined using incoherent neutron scattering experiments, of the materials.