Leroy Elbert Alexander

Bio: Leroy Elbert Alexander is an academic researcher. The author has contributed to research in topics: Powder diffraction & Reflection high-energy electron diffraction. The author has an hindex of 1, co-authored 1 publications receiving 1285 citations.

Remotely actuated polymer nanocomposites--stress-recovery of carbon-nanotube-filled thermoplastic elastomers.

Abstract: Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH1,2. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion3,4,5,6,7,8,9. Here, we demonstrate that the uniform dispersion of 1–5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1–5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system.

Studies on the Relationship Between Water‐satured State and Crystallinity by the Diffraction Method for Moistened Potato Starch

Abstract: Crystallinity was measured by X-ray diffraction method and water-saturated state was determined by means of the moisture contents calculated from the crystallinity for moistened cellulose and potato starch. In the X-ray diffractograms the upper areas which were separated by the straight line joined the points of intensity at 37° and 4° (8°) of diffraction angle was the relative reflection area in the crystalline and amorphous portions, and the lower area was the background of the non-relative reflection area. The upper area separated by the smooth curve joined the minimum intensity at 4° to 37° of diffraction angle corresponded to the crystalline portion and the lower area to the amorphous one. The ratio of the crystalline portion to sum of the crystalline and amorphous portions was considered to be crystallinity. Crystallinity of the air-dried and the moisture-saturated (28%) samples of cellulose were 0.68 and 0.71, resp. The crystallinity of the air-dried and water-saturated (49%) samples of potato starch were 0.24 and 0.32, resp.