Effects of scale and interface on the three-dimensional micromechanics of polymer nanocomposites

Abstract

Nanocomposite materials hold the power to revitalize and revolutionize the field of composite materials. Nanoscaled, even common materials can exhibit strikingly different material properties from the bulk counterparts. If these properties can be accessed at the bulk scale, not only can materials be better tailored to suit various applications, but the possibility of designing multi-functional materials expands exponentially. In this study, the Generalized Method of Cells (GMC) micromechanics model is used to model 3D nanoscale composite architecture, including an interfacial region between the included and matrix phases, and predict the effective viscoelastic properties of a gold nanorod, polymer matrix, nanocomposite. Scale is introduced by referencing the dimensions of the interface to those of the nanorods. Comparisons are made of micromechanical response based on volume fraction and number density, highlighting the scale effects resulting from the high surface area to volume ratio of nanoparticles. Effective composite viscoelastic properties were developed, for static creep, for varying interfacial elastic stiffnesses. These experiments suggest that an elastically stiff interface greatly increases the stiffness of the polymer in response to an ‘instantaneous’ step load, reduces the rapid creep response, and results in a rapid leveling off of the time-dependent strain curves. The response of the composite to increasing stiffness of the interface region eventually reaches a plateau or threshold value, where further increases in the stiffness of the interface produces negligible increases in stiffness, or further reduction in creep response.