Electrospinning polymer concentration

Figure 11 a). SEM micrographs of P(LLA-CL) fibers electrospun from a polymer concentration of 5wt% at different applied voltage (a) 9 kV (b) 12 kV and (c) 15 kV.b) Relation between fiber diameter and applied voltage in the electrospinning with 5wt% P(LLA-CL) solution [64]. 

In addition to the process parameters, a number of system parameters play an important role in fiber formation and the obtained structure. System parameters include molecular weight, molecular weight distribution, polymer architecture, and solution properties. Solution properties play a particularly important role. In relation to their impact on the electrospinning process, these factors can be ranked as follows polymer concentration, solvent volatility, and solution conductivity. 

Generally, a minimum solution concentration is required to obtain uniform fibers from electrospinning. This concentration, polymer chain entanglements are insufficient, and a mixture of beads and fibers is obtained. As the solution concentration increases, the shape of the beads changes from spherical to spindle-like [17],... 

While there is no disagreement on the enhancement of the p phase of PVDF during electrospinning, there is no clear evidence as yet on the mechanism of the conversion of the predominant non-polar a phase to the ferroelectric p phase. There is ambiguity in the literature on whether the rapid solvent evaporation rate or the high stretching forces experienced by the nanofibres prepared from low polymer concentration solutions are responsible for this. 

Experimental results indicate that the diameter of the fiber produced by electrospinning is influenced by the polymer concentration and molecular conformation,such influence is, described by the Berry number, B, on an electrospun poly (L-lactic acid]/chloroform system gives the following equation ... 

Preliminary studies were performed to find the optimum conditions for electrospinning PVA solutions. As the polymer concentration increased, a mixture of beads and fibres was formed. Therefore, a PVA concentration of 10% was used for preparation of electrospun nanofibres. A series of mats were prepared from the 10% PVA solution in a mixture containing various amounts of ferric chloride or ammonium persulfate as oxidant at the 15 kV constant electric field. SEM photomicrographs of electrospun PVA nanofibres from a 10% solution showed the presence of uniform nanofibres with diameters ranging from 150 to 400 nm, with an average diameter of 350 nm. 

The authors conclude that the optimum viscosity for producing uniform fibers by the electrospinning method falls within a large range of values, which is consistent with other observations related to obtaining uniform PAN nanofibers with different polymer concentrations. The nanoparticles from the composite nanoflbers become magnetically harder, with a much larger coercivity than that of the dried nanoparticles. 

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). 

The charge on the electrospinning liquid jet prrmarrly resides on its strrface (Feng 2002 Hohman et al. 2001a Spivak and Dzenis 1999). Typical surface charge densities can be calculated from the feed rate of solution, polymer concentration, and the current flow I across the gap. 

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... 

---