Beads electrospinning

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],... 

The morphologieal struetme ean be slightly changed by changing the solution flow rate as shown in Figure 12. At the flow rate of 0.3 ml/h, a few of big beads were observed on the fibers. The flow rate eould affect electrospinning process. When the flow rate exceeded a critical value, the delivery rate of the solution jet to the capillary tip exceeded the rate at which the solution was removed from the tip by the electric forces. This shift in the mass-balanee resulted in sustained but rmstable jet and fibers with big beads were formed [56]. 

Eong H, Chun 1, Reneker D (1999) Beaded nanofibers formed during electrospinning. Polymer 40 4585—4592. 

Despite the fact that the electrospinning technique is relatively easy to use, there are a number of process parameters that can greatly affect fiber formation and structure. Listed in order of relative impact to the electrospinning process, the most important parameters are applied voltage, polymer flow rate, and capillary-collector distance. All three parameters can influence the formation of nanofibers with bead-like defects. 

Figure 4.4 Example of bead formation during electrospinning SEM micrographs of poly (propyl carbonate) (PPC) beads prepared by electrospinning a PPC solution in dichloro-methane. (Reprinted with permission from Biomaterials, Electrospun aliphatic polycarbonates as tailores tissue scaffold materials by A. Welle, M. Kroger et al., 28, 2211-2219. Copyright...

Duan B, Dong C, Yuan X, Yao K (2004) Electrospinning of chitosan solutions in acetic add with poly(ethylene oxide). J Biomater Sci Polym Ed 15 797-811 Eda G, Shivkumar S (2(X)7) Bead-to-fiber transition in electrospun polystyrene. J Appl Polym Sd 106 475 87... 

PVA, PEO, and PCL nanofibers containing drugs were electrospun, as noted in the aforementioned electrospinning section. Figure 11.11 shows that the electro-spun samples are homogeneous and contain almost no defects, such as beads or... 

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],... 

In the electrospinning technique, the ejected charged jet was affected by electrical forces, so it is needed to have high electrical properties, i.e., a good dielectric constant, to enhance the density of charges at the surface of the jet for better stretching and uniform formation of fibers with bead-free morphology, ... 

The flow rate will determine the amount of solution which will be used for electrospinning. For a certain voltage, there is a corresponding flow rate which maintains the stability of Taylor cone. If the flow rate is increased, there will be a corresponding increase in the fiber diameter or bead size. This is apparent as there... 

In the electrospinning process, the inner diameter of the needle also has some effects. Decreasing the inner diameter can cause an observable decrease in clogging, the number of beads, and the final fiber diameter. 

By considering axisymmetric instabilities of highly conducting viscoeleastic solutions of PEO, in the theoretical studies, a linear stability analysis combined with a model for stable electrospun jet was used to calculate the expected bead growth rate and the bead wave number for given electrospinning conditions. 

Experiments have shown that a minimum viscosity for polymer solution is required to yield fibers without beads, the solution of the PI.50 sample was determined the best electrospinning solution because of the continuous electrospinning process for this study. 

Preparation of PANI nanofiber humidity sensors produced by electrospinning from the DMF solution of PANI, poly(vinyl butyral) (PVB), and PEO were shown. It was concluded that PANI nanofibers with some beads and a small content of PEO revealed... 

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. 

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