Conductive polymers, variable parameters

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 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... 

One of the attractions of the fracture mechanics approach is that the results are geometry independent. This, of course, is subject to conducting tests with valid specimens that meet the dimensions criteria set out in the standards. Considerable work has been conducted with various materials to verify how appropriate these specimen size criteria are for specific polymers and to a.scertain how sensitive the test results are to changes in specimen dimensions and to deviations from the criteria. The specimen thickness is the geometric variable that is considered most, since it governs whether the fracture is plane-strain or not. The effect of specimen thickne.ss B on fracture parameters, e g., K, G, J. and CTOD. has been examined for uPVC [23.61], polycarbonate [23,63], HIPS [64], HOPE [37,59,60,], ABS [65], and ABS PC blends [74], The effect of a/IF on fracture toughness properties is also considered for some of these materials, e g, uPVC [25], HOPE [59.60], polyacetal [68], and polyether sulphone (PES) [70]. 

To control the final fiber properties, a number of variables must be taken into consideration. In addition to the choice of the polymer and solvent [50], it is of importance for other variables, such as (1) applied high voltage, flow rate, tip-to-collector distance, polymer concentration, conductivity, volatility of the solution, temperature, and relative humidity within the chamber [51 -54], All of them can vary the diameter [55], pore size or morphology [51, 56], and surface chemistry [57] of the resulting fibers [35,44, 58, 59], Operating diagrams that are able to predict the experimental parameters required for the process have been proposed [60],... 

When investigating a parameter, whose value can be infinitely variable, such as feed rate, one should vary it logarithmically rather than arithmetically. For instance, 1,2, 4, S,. 1 b m /h or 1, 1.5,2,3,5,7, lOm /h, rather than, say, 2, 4, b, K, 10. By this means a wider picture of trends may be obtained with fewer data points. For polymer dosage, it is generally not possible to be so precise, a.s the numerical value of the polymer dose is not known until after the analyses have been complete, as feed solids concentration can vary from test to test. For a properly conducted test a minimum of five data points are required for a graph. However, if there is not a well-defined trend, then there will be a need for several times that number of data points. 

Many parameters can influence the transformation of polymer solutions into nanofibers through electrospinning. These parameters include (a) solution properties, such as viscosity, elasticity, conductivity and surface tension (b) governing/operating variables, such as hydrostatic pressure in the capillary tube, electric potential at the capillary tip and the gap (distance between the tip and the collecting screen) and (c) ambient parameters such as solution temperature, humidity and air velocity in the electrospinning chamber. ... 

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