Polymer networks are complex systems consisting of molecular components. Whereas the properties of the individual components are typically well understood by most chemists, translating that chemical insight into polymer networks themselves is limited by the statistical and poorly defined nature of network structures. As a result, it is challenging, if not currently impossible, to extrapolate from the molecular behavior of components to the full range of performance and properties of the entire polymer network. Polymer networks therefore present an unrealized, important, and interdisciplinary opportunity to exert molecular-level, chemical control on material macroscopic properties. A barrier to sophisticated molecular approaches to polymer networks is that the techniques for characterizing the molecular structure of networks are often unfamiliar to many scientists. Here, we present a critical overview of the current characterization techniques available to understand the relation between the molecular properties and the resulting performance and behavior of polymer networks, in the absence of added fillers. We highlight the methods available to characterize the chemistry and molecular-level properties of individual polymer strands and junctions, the gelation process by which strands form networks, the structure of the resulting network, and the dynamics and mechanics of the final material. The purpose is not to serve as a detailed manual for conducting these measurements but rather to unify the underlying principles, point out remaining challenges, and provide a concise overview by which chemists can plan characterization strategies that suit their research objectives. Because polymer networks cannot often be sufficiently characterized with a single method, strategic combinations of multiple techniques are typically required for their molecular characterization.

Molecular Characterization of Polymer Networks.

Temperature-dependent mechanical behaviour of PMMA: Experimental analysis and modelling

The effects of pile-up, viscoelasticity and hydrostatic stress on polymer matrix nanoindentation

A review of key developments and pertinent issues in nanoindentation testing of fibre reinforced plastic microstructures

A large percentage of molecular compounds can crystallize in different hydration states. Although hydrated and anhydrous crystal forms can exhibit different physical properties (e.g., solubility, stability, mechanical strength), establishing the contribution water makes to the properties can be elusive. Anhydrous (UA) and dihydrate (UAD) crystal forms of uric acid share a remarkably similar two-dimensional layer structure, though the presence or absence of water between the layers imparts these crystal forms with dramatically different mechanical properties. The quantitative and qualitative differences in how these two materials respond to uniaxial stress were investigated with nanoindentation and atomic force microscopy (AFM) imaging normal to the layer direction. Overall, UA was found to be both substantially harder and more brittle than UAD. Load–displacement curves and AFM images of the UA crystal surface postindent reveal slip planes in preferred crystallographic directions and oriented crack formati...

Xiaoyan Niu

Papers

Effects of experimental variables on PMMA nano-indentation measurements