Chitosan thin films as metal ion sensors and structurally colored coatings

The sensitive and selective detection of heavy metal ions is important in environmental and biomedical applications. A new system incorporating chitosan and optically interesting metallic nanoparticles has been used to create a cost-effective, selective metal ion sensing platform. The system utilizes surface plasmon resonance (SPR) and localized SPR spectroscopy (LSPR), which detect shifts in the oscillation frequency of gold films or nanoparticles induced by changes in the dielectric contrast of the surrounding matrix. High selectivity is achieved by introducing a known chelating polymer as the surrounding matrix. Chitosan is an attractive natural polymer for numerous reasons. It is a renewable resource and waste product of the seafood industry and it is in abundant supply. It is biocompatible, biodegradable, and it has been modified in previous studies to be selective for different metal ions. The dielectric contrast change in a gold nanoparticle containing chitosan thin film has been shown to be an effective sensor for Fe3+ and Cu2+. This system is of interest because of the possibility for sensitivity increase due to modification of the chitosan structure as well as nanoparticle size, shape, and configuration.In addition to being a known chelator, chitosan also exhibits structural color. The structural coloration of chitosan thin films have been studied previously, but new applications such as color tunable paints and cosmetics, as well as packaging and coatings call for structural color which is independent of a silicon substrate. Examples in nature are the intense coloration of butterflies, snakes, hummingbirds and peacocks whose color is created by the differences in the refractive index of stacked thin film layers comprised of alternating materials, such as chitin and air which have a high and low index of refraction respectively. Colored polymer thin films can undergo perceptible color shifts when geometric periodicity of the layers is varied. In our attempts to better understand these processes, stacking of structurally colored polymer thin films of varying index of refraction as well as altering geometries to achieve this effect were investigated herein.M.S., Materials Science and Engineering -- Drexel University, 200

A Simple Model for Nanofiber Formation by Rotary Jet-Spinning

Nanofibers are microstructured materials that span a broad range of applications from tissue engineering scaffolds to polymer transistors. An efficient method of nanofiber production is rotary jet-spinning (RJS), consisting of a perforated reservoir rotating at high speeds along its axis of symmetry, which propels a liquid, polymeric jet out of the reservoir orifice that stretches, dries, and eventually solidifies to form nanoscale fibers. We report a minimal scaling framework complemented by a semi-analytic and numerical approach to characterize the regimes of nanofiber production, leading to a theoretical model for the fiber radius consistent with experimental observations. In addition to providing a mechanism for the formation of nanofibers, our study yields a phase diagram for the design of continuous nanofibers as a function of process parameters with implications for the morphological quality of fibers.Engineering and Applied Science