Electrospinning variables

The effect of electrospinning variables on fiber quality discussed. 

The surface tension seems more likely to be a function of solvent compositions, but is negligibly dependent on the solution concentration. Different solvents may contribute different surface tensions. However, not necessarily a lower surface tension of a solvent will always be more suitable for electrospinning. Generally, surface tension determines the upper and lower boundaries of electrospinning window if all other variables are held constant. The formation of droplets, bead and fibers can be driven by the surface tension of solution and lower surface tension of the spinning solution helps electrospinning to occur at lower electric field [57],... 

Sukigara et al.[78] used RSM analysis (Response Surfaee Methodology) to the experimental results to develop a processing window which will produce nanoscale regenerated silk fibers by electrospinning process. RSM is used in situations where several variables influence a feature (called the response) of the system. The steps in the procedure are described briefly as follows. 

Electrospinning process produces very fine fibers and this is one of the very few methods from which fibers of sub-micron size can be produced. So it becomes immensely important to understand the behavior of fiber diameter and fiber diameter distribution in the electrospun web as impacted by the independent variables (processing parameters). Understanding how fiber diameter and diameter distribution are affected by the processing parameters is essential to produce webs with desired fiber diameter and distribution. 

The following parameters and processing variables affect the electrospinning process (i) system parameters such as molecular weight, molecular weight distribution and architecture (branched, linear, etc.) of the polymer, and polymer solution properties (viscosity, conductivity, dielectric constant, and surface tension, charge carried by the spinning jet) and (ii) process parameters such as electric potential, flow rate and concentration, distance between the capillary and collection screen, ambient parameters... 

Deitzel JM, Kleinmeyer J, Harris D, Tan NCB (2001) The effect of processing variables on the morphology of electrospun nanoflbers and textiles. Polymer 42 261-272 Demir MM, Yilgor I, Yilgor R, Yerman B (2002) Electrospinning of polyurethane fibers. Polymer 43 3303-3309... 

In the present study, CCD was employed to establish relationships between four electrospinning parameters and two responses including the AFD and the CA of elec-trospun Cber mat. The experiment was performed for at least three levels of each factor to Dt a quadratic model. Based on preliminary experiments, polymer solution concentration (X ), applied voltage (X ), tip to collector distance (X ), and volume dw rate (X ) were determined as critical factors with signiCbance effect on AFD and C A of electrospun Cber mat. These factors were fom independent variables and chosen equally spaced, while the AFD and the CA of electrospun Cber mat were dependent variables (responses). The values of -1, 0, and 1 are coded variables corresponding to low, intermediate, and high levels of each factor respectively. The experimental parameters and their levels for four independent variables are shown in Table 1. 

In addition, one-phase smfactant-assisted chemical method has been utilized to synthesize PANI nanofiber, which was doped with CSA and 2-acrylamido-2-methyl-l-propanesulfonic acid, in large quantities [291]. A chemical oxidative polymerization of aniline has been carried out using ammonium peroxydisulfate as an oxidizing agent in the presence of nonionic surfactant. A precipitate of doped emeraldine salt is composed of PANI nanofiber, which has the diameter of 30-50 nm and exhibits the conductivity of 1 -5 S cm at RT. Another piece of research has been done through chemical oxidation polymerization of aniline in a surfactant gel, which was formed by a mixture of hexadecyltrimethylammonium chloride, acetic acid, anihne, and water at - 7 °C [292]. The dendritic PANI nanofiber has the diameter of 60-90 nm and the length of 1 -2 jim. Extended works have been performed by the electrospinning method [293]. It should be taken into account that PANI-CSA fiber shape could be influenced by the synthetic variables such as solvent, surface tension, viscosity, and solution conductivity. 

A novel technique combining coaxial and emulsion electrospinning was presented to produce microstructured core-shell fibers. The design of micro drug reservoirs of variable size within the bulk of fibers combined with a tailored diffusive barrier allows modulating the release kinetics of these novel carriers. A... 

Response surface methodology (RSM) is a combination of rrtathematical and statistical techniques used to evalirate the relationship between a set of corrtrollable experimental factors and observed results. This optimization process is used in situations where several input variables influence some output variables of the system. The main goal of RSM is to optimize the response, which is influenced by several independent variables, with minimum number of experiments [9,10]. Therefore, the application of RSM in electrospinning process will be helpful in effort to find and optimize the elec-trospun nanofibers properties. 

It is well known that the valne of CAfor hydrophilie snifaces is less than 90°. Fabrication of these snifaces has attracted considerable interest for both fundamental researeh and practical studies. So, the goal of the present stucfy is to minimize the CA of elec-trospun nanofibers. The optimal conditions of the electrospinning parameters were established from the quadratic form of the RSM. Independent variables namely, solution concentration, applied voltage, spinning distance, and volume flow rate were set in range and dependent variable (CA) was fixed at minimum. The optimal conditions in the tested range for minimum CA of electrospun fiber mat are shown in Table 5. 

The relative importance of electrospinning parameters on the value of CA calculated by Equation (4) and is shown in Figure 6. It can be seen that, all of the input variables have considerable effects on the CA of electrospun liber mat Nevertheless, the solution concentration with relative importance of 49.69% is found to be most important factor affecting the C A of electrospun nanofibers. These results are in close agreement with those obtained with RSM. 

The optimal values of the electrospinning parameters were established from the quadratic form of the RSM. Independent variables (solution concentration, applied volt-... 

Electrospinning parameters are the variables which can be controlled and adjusted in order to manipulate the morphology and feamres of the electrospun nanofibers. Electrospinning parameters are classified into three main categories which are (i) processing (controlled) variables, (ii) ambient (uncontrolled) variables, and (iii) the solution variables (Huang et al. 2003 Pham et al. 2006 Zander 2013). Electrospinning parameters are summarized in Table 1. 

Polymer solution parameters are certain variables related to the physical properties of the polymer solution used for electrospinning nanofibers such as polymer concentration, polymer solution viscosity, polymer molecular weight, solution charge density, conductivity, volatility, surface tension, dielectric constant, and dipole moment. These variables are hard to be altered since changing one of those variables would consequently change some of the others. An example of that is the alteration in the polymer solution viscosity upon changing its conductivity (Pham et al. 2006). 

Although electrospinning appear to be a highly sophisticated technique dealing with many parameters and variables, most of these variables can be manipulated in order to produce nanofibrous materials with certain nanofeatures according to the targeted application. 

The principle variables that govern nanofiber quality (or determine if electrospinning will occur at aU) are the average molecular weight of the polymer, the nature of the solvent, and the magnitude of the electric field used to induce electrospinning. 

Even within the concentration regime that obtains electrospinning, the quality of nanofibers electrospun can be quite variable. Koski et al. (2004), electrospinning poly(vinyl alcohol) (PVA) in aqueous solution at... 

Theron and colleagues (Theron et al. 2001) found a power-law dependence of on the variables of applied potential V, the feed rate Q, the polymer concentration C, the molecular weight of the polymer, and the gap distance, in electrospinning PEO solutions. Values of measured at a point just below the Taylor s cone in electrospinning PCL solutions showed a similar dependence on V and on the feed rate. The mass charge density on the dry... 

Two classes of variables that affect electrospinning can be identified from the literature the materials variables relating to polymer and solvent characteristics and the process variables pertaining to either the choice of equipment (e.g., the collector plate material or the spinning environment) or the operating parameters. For convenience of description these are categorized as shown in Scheme 4.1 as the materials variables (A, B, and C) and process variables (D, E, F, and G). However, because these are interrelated, a small... 

Scheme 4.1 The basic materials and process variables involved in electrospinning of polymer nanofibers. Electrospinning schematic reproduced here with pennission from Hsu and Shivkumar (2004b). Copyright 2004. Springer Science and Business...

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