Dissolution and regeneration of Bombyx mori silk fibroin using ionic liquids

In this work, the suitability of imidazolium-based ionic liquid solvents is investigated for the dissolution and regeneration of silkworm (Bombyx mori) silk. Within an ionic liquid the anion plays a larger role in dictating the ultimate solubility of the silk. The dissolution of the silk in the ionic liquid is confirmed using wide-angle X-ray scattering. The dissolved silk is also processed into 100 mum-thick, two-dimensional films, and the structure of these films is examined. The rinse solvent, acetonitrile or methanol, has a profound impact on both the topography of the films and the secondary structure of the silk protein. The image depicts a silkworm cocoon dissolved in 1-butyl-3-methylimidazolium chloride and then regenerated as a film with birefringence.     

High resolution electron microscopy of ordered polymers and organic molecular crystals: Recent developments and future possibilities

High Resolution Electron Microscopy (HREM) has made it possible to directly image the detailed organization of a variety of polymers and organic molecular crystals. For organic materials it is imperative to use low dose techniques that minimize the structural reorganizations that inevitably occur during electron beam irradiation. This article reviews recent developments in low dose HREM from our own laboratory and elsewhere. The developments in closely related microstructural characterization techniques are also reviewed. In the future, the ability to correct the spherical aberration of the objective lens, the use of low voltages to increase contrast, and the use of time‐resolved techniques are expected to open new avenues for the ultrastructural investigations of organic materials. New sample preparation techniques, such as the ability to make thin samples by focused ion beam (FIBs), to cut samples with an oscillating diamond knife, and to more conveniently prepare cryogenically solidified specimens, are also expected to be of increasing importance. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1749–1778, 2005     

Imaging of crystal morphology and molecular simulations of surface energies in pentacene thin films

We have investigated the crystal growth of the organic semiconductor pentacene by complementing molecular simulations of surface energies with experimental images of pentacene films. Pentacene thin films having variations in thickness and grain size were produced by vacuum sublimation. Large (approximately 20 microm) faceted crystals grew on top of the underlying polycrystalline thin film. The films were characterized using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Single crystals most commonly grew in a truncated diamond shape with the largest crystal face, (001), growing parallel to the substrate. Crystal morphologies and surface energies were calculated using force field-based molecular simulations. The (001) surface was found to have the lowest energy, at 76 mJ/m(2), which was consistent with experimental observations of crystal face size. It was demonstrated that the morphology of the large faceted crystals approached the equilibrium growth shape of pentacene. From contact angle measurements, the critical surface tension of textured pentacene thin films in air was determined to be 34 mJ/m(2).