Addition of nanoclays or other nanoparticles into various polymers to produce nanocomposites has been extensively utilized in an attempt to enhance the mechanical, physical, and thermal properties of polymers. While some interesting properties have been demonstrated, the resulting nanocomposites have yet to realize their full potential. Nanoparticles in general, and nanoclays in particular, with their nanometer size, high surface area, and the associated predominance of interfaces in the nanocomposites, can function as structure and morphology directors, for example stabilizing a metastable or conventionally inaccessible polymer phase, or introduce new energy dissipation mechanisms. Thus, what distinguishes nanoparticles from conventional micrometer-size rigid reinforcements is that their role might not be limited to only adding stiffness to the polymer, but also to directing morphology, as well as introducing new energy-dissipation mechanisms leading to enhanced toughness in the nanocomposites. Herein we demonstrate this potential by reporting a remarkable (order of magnitude) increase in toughness with a concurrent increase in stiffness in a poly(vinylidene fluoride) (PVDF) nanocomposite.The kinetics of crystallite growth and the details of crystallite morphology of semicrystalline polymers can be affected by the presence of layered silicates. [1,2] Although some changes in morphology have been described in polymer/nanoparticle hybrids, [3±7] near-total stabilization and control of a crystalline phase, coupled with dramatic enhancements in materials properties, has not yet been reported. PVDF is an important engineering plastic. It is used extensively in the pulp and paper industry due to its resistance to halogens and acids, in nuclear-waste processing for radiation-, and hot-acid applications, and in the chemical processing industry for chemical and high-temperature applications. It is also used in various device applications, due to its unique piezoelectric [8±10] and pyroelectric [11] properties. There are five known crystalline forms or polymorphs of PVDF: a, b, c, d, and e.[12] The a phase is the most common in melt crystallization, and remains the dominant crystalline form versus the b, and c phases. The c phase does not form except at high temperatures and pressures. Earlier reports have shown that the a phase (chain conformationÐtrans-gauche trans-gauche, tgis inactive with respect to piezo-and pyroelectric properties, while the b form (all trans) exhibits the most activity, and is thus the focus for electromechanical and electroacoustic transducer applications. Thus, the b form has great technological utility and there have been numerous attempts to stabilize this phase. For example, the b form of the PVDF has been obtained by careful crystallization from solution, [13] by melt crystallization at high pressure, by application of a strong electric field, [14] by molecular epitaxy, [15] and by preparing a carbon-coated, highly oriented ultrathin film.[16] Earlier reports have indicated the possibility...

Silk fibroin has been successfully used as a biomaterial for tissue regeneration. In order to prepare silk fibroin biomaterials for human implantation a series of processing steps are required to purify the protein. Degumming to remove inflammatory sericin is a crucial step related to biocompatibility and variability in the material. Detailed characterization of silk fibroin degumming is reported. The degumming conditions significantly affected cell viability on the silk fibroin material and the ability to form three-dimensional porous scaffolds from the silk fibroin, but did not affect macrophage activation or β-sheet content in the materials formed. Methods are also provided to determine the content of residual sericin in silk fibroin solutions and to assess changes in silk fibroin molecular weight. Amino acid composition analysis was used to detect sericin residuals in silk solutions with a detection limit between 1.0% and 10% wt/wt, while fluorescence spectroscopy was used to reproducibly distinguish between silk samples with different molecular weights. Both methods are simple and require minimal sample volume, providing useful quality control tools for silk fibroin preparation processes.

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We examined the possibility that people hold multiple stereotypes of the elderly. Subjects were male and female university students. In the first phase of our study, stereotype content was sampled by asking subjects to describe the typical old person. In the second phase of the study, different subjects sorted traits from Phase 1 descriptions into one or more groups. Each group contained those traits that subjects felt could be found in one and the same older adult. Attitudes toward the stereotypes were also assessed. A distance matrix, based on the number of subjects who sorted each pair of traits into different groups, was analyzed by hierarchical cluster analysis. Evidence for multiple stereotypes was found both in the presence of contradictory traits given in Phase 1 descriptions and in the structure of the clusters. Different attitudes are identified for the cluster-defined stereotypes.