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Tham khảo tài liệu 'solar cells dye sensitized devices part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 Solar Cells rDye-Sensitized Devices 2.2.4.4 Tip to collector distance TCD The distance of between capillary tip and collector can also influence fiber size by 1-2 orders of magnitude. Additionally this distance can dictate whether the end result is electrospinning or electrospraying. Doshi and Reneker found that the fiber diameter decreased with increasing distances from the Taylor cone 65 . 2.2.4.5 Solvent volatility Choice of solvent is also critical as to whether fibers are capable of forming as well as influencing fiber porosity. In order for sufficient solvent evaporation to occur between the capillary tip and the collector a volatile solvent must be used. As the fiber jet travels through the atmosphere toward the collector a phase separation occurs before the solid polymer fibers are deposited a process that is greatly influenced by volatility of the solvent. Zhao et al. examined the structural properties of 15 wt of poly Vinylidene Fluoride nanofibers with different volume ratios in DMF Acetone 66 . when DMF was used as the solvent without acetone bead-fibers were found when 9 1 DMF acetone was used a s the solvent in the polymer solution beads in the electrospun almost disappeared. Furthermore the ultafine fibers without beads demonstrated clearly when the acetone amount in the solution increased to 20 . Acetone is more volatile than DMF. Furthermore the changes of solution properties by the addition of acetone could probably improve the electrospun membrane morphology and decrease the possibility of bead formation. 3. Results 3.1 Preparation of electrospun poly vinylidene fluoride-hexafluoropropylene PVDF-HFP nanofibers Generally in the electrospinning method the changing of the parameters had a great effect on fiber morphology. To prepare the electrospun PVDF-HFP nanofiber films with the suitable morphology we prepared the electrospun PVDF-HFP nanofiber films by several parameters such as the applied voltage voltage supplier NNC-ESP100 Nano NC Co. .
