# Mechanical and Dielectric Properties of Aligned Electrospun Fibers
## 1 Introduction
### Parameters and Parameter Optimizations  
Important parameters that affect the quality of electrospun fibers formed from polymer solutions can be categorized as solution-specific parameters, process-specific parameters, and environmental-specific parameters [6; 17; 71]. 1. Solution parameters: The solution-specific parameters include viscosity, polymer concentration, surface tension, conductivity, and evaporation rate of solvent [72; 73; 74; 75; 76; 18]. It is observed that low viscosity is typically responsible for bead generation and significant increase in fiber diameter. A similar conclusion was made on polyacrylamide-trie/dimethylformamide (PAN/DMF) solution where beads were easier to form at low concentration of 5 wt.% than that formed at higher concentration of 7 wt.% [77; 78]. Typically, viscosity and concentration are directly proportional to each other [79]. \begin{table}
\begin{tabular}{c c c} \hline
**Authors** & **Year** & **Main Criteria of Review Papers** \\ \hline [PERSON] et al. & 2003 & \
\begin{tabular}{c} Processing, structure, characterization, applications, modeling and simulation, \\ and different polymers in solution and melt form [17] \\ \end{tabular} \\ \hline [PERSON] et al. & 2006 & Tissue engineering (scaffolds) [66] \\ \hline [PERSON] and [PERSON] & 2010 & Polymers, parameters, melt electrospinning, and applications [6] \\ \hline [PERSON] et al. & 2012 & Scale-up challenges and applications [14] \\ \hline [PERSON] et al. & 2014 & Nanofiber yarns and nanofiber alignment [67] \\ \hline [PERSON] et al. & 2015 &
\begin{tabular}{c} 1D nanomaterials have high surface-area-to-volume (specific surface area), high aspect \\ ratio, and high pore volume. Well-aligned and highly ordered are suitable for energy \\ harvesting and storage devices. More advantageous than conventional materials [68] \\ \end{tabular} \\ \hline [PERSON] et al. & 2015 & Desalination [29] \\ \hline [PERSON] et al. & 2016 & Energy storage [12] \\ \hline [PERSON] et al. & 2016 & Tissue regeneration, energy conversion and storage, and water treatment [23] \\ \hline [PERSON] et al. & 2017 & Water purification [69] \\ \hline [PERSON] et al. & 2018 & Food packaging [15] \\ \hline [PERSON] et al. & 2019 & Electrical and mechanical performance of polymer nanocomposites [70] \\ \hline \end{tabular}
\end{table} 
Table 1: Recent review papers on electrospun nanofibers. Additionally, polymer concentration directly controls fiber diameter [79]. In general, an increase in fiber diameter can be achieved by increasing the polymer concentration. Higher surface tension causes bead formation and reduced surface tension favors smooth fiber formation [80]. 2. Process parameters: Applied voltage, distance between the nozzle tip and collector, rotating speed of the collector (if drum is used), and solution feed rate are the parameters that are regarded as process specific [18; 81; 82; 83]. In general, fiber diameter can be reduced by increasing applied voltage and vice versa. If the applied voltage reaches a critical value, a charged jet initiates the electrospinning process. This critical voltage is closely related to surface tension of the solution. [PERSON] et al. (2003) reported that there was a linear relationship between voltage applied and surface tension of polystyrene (PS) dissolved in a mixture of tetrahydrofuran and DMF [84]. The distance between the tip and the collector mainly controls fiber solidification because a minimum distance is required to allow the fibers sufficient time to dry before reaching the collector. Distances that are too close or too far can cause beads to form. [PERSON] et al. (2010) studied 7 wt.% PAN/DMF electrospun at 2-10 cm away from nozzle tip. The experiments concluded that beads were producing until the distance reached 7 cm [78]. Longer distance between nozzle tip and collector produced bead free fibers. 3. Environmental parameters: Humidity and temperature are treated as environment-specific parameters [85; 86; 18]. According to [PERSON] et al.