Relationship between electrospun fibers and spinning conditions are investigated from the view point of jet profiles such as diameter distribution, jet velocity, and the evaporation rate of solvent from the surface of jet in solution electrospinning process by changing (i) the applied voltage and (ii) the relative humidity of ambient air. Profiles of jets near the droplet at the tip of needle are measured as functions of the position along the spinning line by using photographs. The measured profiles of jet can be fitted nicely by the analytic expression of spinning profile for a non-evaporating Newtonian fluid, which enables us to calculate the velocity profile of jets and the evaporation rate of solvent from the jet as a function of the position along the spinning line. Changing the applied voltage, it is found that the jet velocity and the evaporation rate in our measured region are decreased and beaded fibers are increased when increasing the applied voltage, on the other hand the total amount of evaporated solvent from a jet in our measured region is too small to affect the profile of jet and to change the viscosity of solution in the jet. Changing the relative humidity, it is found that profiles of jets are almost the same except for the evaporation rate. The evaporation rate in our measured region is increased by decreasing the relative humidity. In the lower humidity region, less than 60% of humidity, beaded fibers are hardly formed, but in the higher humidity region, more than 60%, beaded fibers are increased with increasing humidity. From the results in two conditions (i) and (ii), it is found that the beaded fibers are easily formed as the evaporation rate of solvent becomes smaller.
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