Mechanical Properties of Thin Glassy Polymer Films Filled with Spherical Polymer-Grafted Nanoparticles

Abstract

It is commonly accepted that the addition of spherical nanoparticles (NPs) cannot simultaneously improve the elastic modulus, the yield stress, and the ductility of an amorphous glassy polymer matrix. In contrast to this conventional wisdom, we show that ductility can be substantially increased, while maintaining gains in the elastic modulus and yield stress, in glassy nanocomposite films composed of spherical silica NPs grafted with polystyrene (PS) chains in a PS matrix. The key to these improvements are (i) uniform NP spatial dispersion and (ii) strong interfacial binding between NPs and the matrix, by making the grafted chains sufficiently long relative to the matrix. Strikingly, the optimal conditions for the mechanical reinforcement of the same nanocomposite material in the melt state is completely different, requiring the presence of spatially extended NP clusters. Evidently, NP spatial dispersions that optimize material properties are crucially sensitive to the state (melt versus glass) of the polymeric material.

Enhanced Glassy State Mechanical Properties of Polymer Nanocomposites via Supramolecular Interactions

“…We find that the mechanical response in the glassy state surpass those obtained previously, 5 where there was no specific interactions between the grafts and the matrix chains, except for transient chain entanglements. Our results clearly show that both good NP dispersion and strong adhesion between the NP and the matrix are critical to optimizing the glassy state response of PNCs.…”

Perspective: Outstanding theoretical questions in polymer-nanoparticle hybrids

“…264 We now move to the glassy state, where there is very little systematic experimental work. Maillard et al 280 found that the Young's modulus, the yield strain, and the strain-to-failure can all be tuned by varying the polymer grafted NP dispersion state in polymer glasses. To our knowledge, the only systematic theoretical work in this area is by Riggleman, de Pablo, and Douglas, 97 who have looked at the entanglement network in these situations and how it is modified under the action of extension.…”

Mechanical responses of a polymer graphene-sheet nano-sandwich

“…The nano-bubble inflation method of McKenna and coworkers [14e18] has also been expanded recently to measure the mechanical properties of 800 nm  2.6 mm rectangular ultrathin polymer films [30] as well as to polycarbonate films as thin as 3 nm [18]. More recently Maillard et al [31] used a laser confocal microscope profilometer to image 500 mm  5 mm rectangular nearnanometric scale thickness films of a glassy polystyrene filled with silica nanoparticles. However, to the best of our knowledge, the nano-bubble inflation or bulge testing methods have not been exploited to study such a nano-sandwich model composite as that investigated in the present work.…”