Anomalous Strain Recovery after Stress Removal of Graded Rubber.

Mechanical responses after the uniaxial deformation of graded styrene-butadiene rubber (SBR) with a gradient in the crosslink points in the thickness direction were investigated as compared with those of homogenously vulcanized SBR samples. The elongational residual strain of a graded sample was found to depend on the part with a high crosslink density. Therefore, it showed good rubber elasticity. After stress removal, moreover, the graded sample showed a marked warpage. This suggested that shrinking stress acted on the surface with a high crosslink density, which would avoid a crack growth on the surface. The sample shape was then recovered to be flat very slowly, indicating that the shrinking stress worked for a long time. This unique rubber elasticity, i.e., slow strain recovery with an excellent strain recovery, makes graded rubber highly significant.

Metal latticeworks formed by self-organization in oscillatory electrodeposition.

Strikingly well-ordered Sn latticeworks, standing perpendicular to the substrate, are formed spontaneously in oscillatory electrodeposition. Cooperation of various processes, such as needle formation by autocatalytic crystal growth, cuboid formation under a reaction-limited condition, and autocatalytic oxidation at closest-packed surfaces, enabled the self-organization of the latticeworks. The mechanism is generally applicable to deposition of other metals such as Zn, Pb, and Cu. The present work has opened a promising, unique field toward the formation of highly ordered 3-D micro- or nanostructures at solid surfaces.

Structures of Fibrous Supramolecular Assemblies Constructed by Amino Acid Surfactants: Investigation by AFM, SANS, and SAXS.

Aqueous gel-like solutions of N-acyl-L-aspartic acids (C(n)Asp, n=14, 16, 18) and N-dodecanoyl-beta-alanine (C(12)Ala) were prepared at pH 5-6 at room temperature. Structures of supramolecular assemblies in the solutions were investigated by atomic force microscopy (AFM), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS). The cross-sectional radii, 22-30 Å, of helical, fibrous assemblies were obtained from analysis of SANS for 1% gel-like C(n)Asp solutions. Three Bragg spacings were observed in a SANS spectrum for a 6% C(16)Asp solution. C(n)Asp molecules are associated into the unit chain of a helical bilayer strand with a diameter of 50-60 Å. Unit chains where linear bilayers twist form a double strand with helical sense of approximately 650-Å pitch. It was confirmed from AFM images that cylindrical fibers in a gel-like C(12)Ala solution had a circular cross-section. The SAXS spectrum showed characteristic Bragg spacings. Cylindrical C(12)Ala fibers consist of multilamellar layers of period approximately 34-Å. The fibers are laterally organized with period 365-380 Å. Copyright 2000 Academic Press.