The electric currents between electrodes in the electrospinning process are based on the movement of charge carriers through the spinning space. The majority of the charge carriers are formed by ionization of the air close to the metallic needle and to the polymer jet. The salt contained in the polymer solution contributes to the concentration of charge carriers, depending on its amount. The conductivity of polymer jets does not significantly affect the current since the jets do not link the electrodes. 1. Introduction Electric current was studied across various electrospinning (ES) techniques, namely, in the needle ES [1–14], rod ES [15, 16], and roller ES [17]. In the needle ES, two sorts of experimental arrangement were employed: the “point-plate” geometry [7, 9, 11] and “parallel-plate” geometry [4, 6, 9, 13]. Advantages of the latter geometry are explained in [8]. It mainly consists of an easier interpretation of measured data in the uniform electric field of the parallel-plate spinner. In the above mentioned works, the dependence of the electric current in the jet on various independent process parameters was studied, such as solution feed, solution conductivity, applied voltage, the diameter of the hollow needle, relative humidity, and some geometrical characteristics. The results of these experiments were formulated in a number of both phenomenological and theoretical equations, such as the dependence of the current in a jet on independent ES parameters [6], as shown in (1) and (2). The empirical equation (1) says that the current was found to scale as where is the current flowing through a jet, is the field strength, is the flow rate, and is the conductivity of the solution. Equation (1) may be applied to various polymer solutions in nonaqueous solvents. Theoretical Equation (2) describes current in a jet as where is the radius of the jet, , , and as in (1) above and is the surface charge density. The first term in (2) refers to the conduction current and the second to the advection of the surface charge. It is the aim of the present work to study the dependence of current on various process parameters in more detail and to explain the results in terms of the mechanism of charge transport. 2. Experimental In the experimental part, one preliminary test and four groups of experiments were performed as follows. Preliminary Test. Measurement of changes in the current depending on the measuring device’s needle protrusion length. Group of Experiments 1. Measurement of changes in the current caused by polymer concentration, solution viscosity,
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