Environmental Effects on Structure and Morphology in Electrospun Polymer Nanofibers John Rabolt, University of Delaware, DMR Nylon 6 is known to exist in two well characterized crystal forms. The structure of the α form consists of adjacent polymer chains oriented in opposite directions relative to each other (anti-parallel), thereby maximizing hydrogen bonding interactions. It is the more thermodynamically stable of the two crystal forms due to the optimized hydrogen bonding interactions in this structure. The γ form (produced by ling term (days) exposure to KI + I 2 solution) consists of adjacent Nylon 6 chains oriented parallel to each other, resulting in a less efficient hydrogen bonding network and thus a less thermodynamically favorable (metastable) crystalline form. The role of solvent evaporation on the crystalline state of electrospun Nylon 6 fibers was examined by electrospinning into a closed chamber filled with different concentrations of solvent vapor. It was found that the thermodynamically stable α crystalline form became increasingly present in Nylon 6 fibers electrospun out of both 1,1,1,3,3,3-hexafluoro-2- propanol (HFIP) and formic acid as the vapor phase solvent concentration increased. It is believed that the formation of the metastable γ crystalline form is due to the fast solvent evaporation kinetics associated with the electrospinning process. By varying the vapor phase concentration and thus the rate of solvent evaporation during electrospinning, we were able to control the resulting crystal structure of the electrospun Nylon 6, as shown by XRD, Raman and FTIR.. Figure 1. X-ray profiles of Nylon 6 processed from HFIP: (a) KI/I 2 treated cast film; fibers electrospun (b) without the environmental chamber and with varying amounts of evaporated HFIP: (c) 0g, (d) 0.75g, (e) 1.5g, (f) 2.25g, (g) 2.6g, (h) 3.0g, (i) 4.5g; and (j) a solvent cast film.

The Second US-China Workshop on Nanostructured Materials for Global Energy and Environmental Challenges was held in Changzhou, China, October 17-18, This workshop presented the opportunity to not only hear about some of the work, being carried out in the field but also help plan multidisciplinary, international collaborations on nanostructured materials. Since Carl Giller (supported on this grant) was one of only ten graduate students at the workshop, he was able to interact with the many scientists and engineers who came from different parts of the world and who had diversified professional backgrounds. The opportunity to interact with graduate students from different parts of both the US and China enriched his experience, and gave him a perspective on some of the research problems that academic labs are currently attempting to solve. Rabolt and Giller were able to make several contacts within the Chinese Academy of Sciences and at Tsinghua University that have lead to collaborations on electrospun polymer nanofibers. In addition, Giller met a Chinese student, Ming Yang (Tianjin University), and helped him with the preparation of CV/essays/etc. required for graduate school applications. As a result Ming Yang will be attending graduate school in chemical engineering at Tufts University this Fall. Figure 2. A group of US and Chinese students that met while participating in the NSF sponsored “US-China Workshop on Nanostructured Materials for Global Energy and Environmental Challenges" sponsored through the IMI at Northwestern and held in Changzhou, China in October.. As a result, Carl Giller (4 th from right), currently supported on this grant, has been working with Ming Yang (Tianjin University) (on left) on science writing and resume preparation. Environmental Effects on Structure and Morphology in Electrospun Polymer Nanofibers John Rabolt, University of Delaware, DMR