Document Type thesis Author Name Eda, Goki URN etd-042706-135317 Title Effects of Solution Rheology on Electrospinning of Polystyrene Degree MS Department Materials Science & Engineering Advisors Satya Shivkumar, Advisor Md. Maniruzzaman, Committee Member Richard D. Sisson, Jr., Committee Member Jianyu Liang, Committee Member Keywords polymer polystyrene electrospinning rheology Date of Presentation/Defense 2006-04-20 Availability unrestricted
The effects of fundamental solution parameters including polymer molecular weight, concentration and solvent on electrospinning of polystyrene were investigated. Each parameter was found to play a vital role in determining the morphology of beads and fibers. For dilute to semi-dilute solutions, a wide range of bead structures including wrinkled beads, cups, dishes, and toroids were observed when a volatile solvent, tetrahydrofuran, was used. Various rheological regimes where these structures may be obtained were identified. The morphological transition from bead to fiber was characterized by two critical concentrations, Ci and Cf, at which incipient and complete fibers may be observed respectively. These values were determined as a function of molecular weight. A comparison with the models proposed in the literature indicated that solvent evaporation may play an important role in jet stabilization. The fiber diameter and distribution was found to decrease significantly with molecular weight at the critical concentration, Cf. The use of N,N-dimethylformamide, a solvent with relatively high dielectric constant, also resulted in an appreciable reduction in fiber diameter and improved uniformity. The observation of solution jet evolution during the process with high speed camera (2000 frames/s) indicated that solvents have a significant influence on the jet breakdown behavior. Two types of behavior were identified based on the extent of extensional flow, bending instability, and the number of secondary jets. Solvents with high dielectric constant were found to induce extensive bending instability, which resulted in extremely fine microstructures of electrospun polymer.
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