Polymer nanocomposites represent an important class of materials both from a scientific and an industrial standpoint. From the study of low volume fraction blends with a broad range of polymers to so-called “bricks-and-mortar” systems containing much higher nanoparticle concentrations, many compositions have been studied and impressive properties have been described.  At the same time, in spite of decades of work in this area, critical questions concerning the behavior of these materials remain to this day. The behavior of the confined polymer phase remains poorly understood and the properties of intercalated stacks of layers continue to be debated, in spite of the ubiquity of these features in polymer / clay nanocomposites. Various analytical models have been used over the years to describe mechanical and barrier performance in these systems – but how general are these results?<br/><br/>Here we present a summary of an in-depth investigation of two families of spray-deposited polymer / clay nanolaminates – nanocomposites consisting of highly aligned clay layers embedded in a polymer matrix, spanning the entire composition range from pure polymer to pure (modified) clay. The polymer phase is entirely amorphous and the chemistry of these systems is effectively identical except for a subtle change that enables us to turn intercalation off in one system while leaving it on in the other. Scanning electron microscopy and 2D wide-angle x-ray diffraction provide the needed structural details, while dynamic mechanical analyses and oxygen permeation measurements are used to assess changes in elastic and barrier performance, respectively. The observed trends highlight the insufficiencies in the effective aspect ratio model commonly invoked in the field.  Micromechanical models commonly used to describe nanocomposite performance are unable to account for the modulus variations in what is otherwise an ideal model system, with well-aligned layers and a fully amorphous polymer phase. These same materials produce oxygen permeation results dominated by the single layer aspect ratio regardless of intercalation state, and emphasize the importance of the polymer phase in determining the barrier performance of high clay content bricks-and-mortar structures in particular. In sum, these results provide useful guidance as far as the modeling of these complex and interesting materials is concerned.

Polymer nanolaminates and the consequences of intercalation

251st National Meeting (2016)

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