Nanocomposites: stiffer by design.
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Comment↗
Biomedical subjects
Evangelos Manias
Publications and source records attributed to Evangelos Manias.
Nested self-similar wrinkling patterns in skins.
Stiff thin films on soft substrates are both ancient and commonplace in nature; for instance, animal skin comprises a stiff epidermis attached to a soft dermis. Although more recent and rare, artificial skins are increasingly used in a broad range of applications, including flexible electronics, tunable diffraction gratings, force spectroscopy in cells, modern metrology methods, and other devices. Here we show that model elastomeric artificial skins wrinkle in a hierarchical pattern consisting of self-similar buckles extending over five orders of magnitude in length scale, ranging from a few nanometres to a few millimetres. We provide a mechanism for the formation of this hierarchical wrinkling pattern, and quantify our experimental findings with both computations and a simple scaling theory. This allows us to harness the substrates for applications. In particular, we show how to use the multigeneration-wrinkled substrate for separating particles based on their size, while simultaneously forming linear chains of monodisperse particles.
Cross-Linking Reagents↗
Low permeability biomedical polyurethane nanocomposites.
In this article we describe our continuing research on a novel nanocomposite approach for reducing gas permeability through biomedical polyurethane membranes. Nanocomposites were prepared using commercially available poly(urethane urea)s (PUU) and two organically modified layered silicates (OLS). Wide-angle X-ray diffraction experiments showed that the silicate layer spacing in the nanocomposites increased significantly compared with the neat OLS, signifying the formation of intercalated PUU/OLS structures. The nanocomposite materials exhibit increased modulus with increasing OLS content, while maintaining polymer strength and ductility. Water vapor permeability was reduced by about fivefold at the highest OLS contents, as a result of PUU/inorganic composite formation.
Calorimetry, Differential Scanning↗
Solid-state microstructure of poly(l-lactide) and l-lactide/meso-lactide random copolymers by atomic force microscopy (AFM).
Tapping mode atomic force microscopy was used to investigate the lamellar morphology of poly(l-lactide) and two poly(l-lactide-co-meso-lactide) random copolymers containing 3% and 6% meso-lactide. Samples were isothermally crystallized at selected temperatures, and qualitative and quantitative analyses of lamellar structure were performed using height and phase images. This is the first study of the morphology of polylactide stereocopolymers using a real-space probe, and the important effects of scanning parameters on the acquired images are described. More open spherulites with an abundance of screw dislocations between edge-on lamellar stacks were observed in samples crystallized at higher temperatures. Mean lamellar thicknesses are lower for the random copolymers compared to PLLA, particularly at lower DeltaT, in agreement with the results of our previous small-angle X-ray scattering (SAXS) experiments. Mean lamellar thicknesses derived from the current real-space examination are in good agreement with those determined previously from SAXS. Internal surfaces-from microtomed specimens-were also studied to investigate the bulk crystal morphology. Although quantitative analysis was not feasible (for reasons discussed in the text), lamellar organization similar to that seen in the surface experiments is observed at high magnifications.
Biocompatible Materials↗