| With the hint as to the mechanism of spider spinning and the principle of bubble dynamics, a new technology named bubble-electrospinning is proposed and some research results have been achieved so far. However, some problems such as unstability of nanofiber morphology exist during spinning process. In order to controlling nanofiber morphologies and developing applications, we first analyzed the basic spinning principle and classification methods. On the basis, we studied the controlling of nanofiber morphologies by designing relative experiments.In order to understand the effect of bubble dynamics on nanofiber morphologies, we analyzed the effect of bubble size, bubble membrane shape, bubble thickness and bubble thermodynamic parameters on morphologies of bubble electrospun products, and we indicated that:(1) when bubbles increased to a threshold, big bubbles would rupture into daughter bubbles or secondary daughter bubbles to make the diameter of fabricated nanofibers decreasing;(2) when a piece of bubble film with the wideness of a met a=10.6h(h is the thickness of bubble membrane), microspheres would be formed; when10.6h <a<4πh, irregular products such as spheroids, rhombohtedron and spindle would be formed; when, smo a=4πh oth cylinder nanofibers would be formed and when a>>4πh, stripe fibers would be formed;(3) the average diameter of nanofibers would increase along with the increase of bubble inner temperature when the environment temperature kept the same; and when bubble inner temperature remained unchanged, the average diameter of nanofibers would decrease in accordance with the increase of environment temperature. When the solution temperature increased, the viscosity would decrease and the conductivity would increase so that the average diameter of fabricated nanofibers would decrease. The bubble deformation process under electrical field is filmed by high speed camera and we obtain the critical electric field intensity, the critical half angle of tailor corn is 31.9°and the critical thickness of bubble membrane h=0.85h0(h0 is the initial thickness of bubble membrane). According to Bernoulli equation, we can calculate preliminarily that the initial velocity of charged jets is 97m/s. and the initial velocity of charged jets can be obtained in accordance with dimension analysis so that we can make sure key parameters which affect the bubble ruptures and the speed of charged jets.In order to understand the effect of spinning parameter on nanofiber morphologies, in the beginning, we analyzed the effect dynamic theoretically of each parameter, presented prediction models and did experimental certification. Researches showed that:(1) The higher of current, the thinner of nanofiber diameter.(2) In initial phase, the relation between jet radius and collection distance met r~z-1/2 and in unsteady stage, it met r~z-1/4.(3) Lines linking both ends of a equipotential line were parallel to each other so that fabricated nanofibers were high orientation distribution by simulating the distribution of electrical field using ANSYS software.(4) The relation between ultrasonic vibration time and nanofiber diameter was d ∝ t0.33 and the relation between vibration power and nanofiber diameter was d ∝ P1.22.(5) Relations among viscosity, concentration and diameter were analyzed respectively. By spinning fibroin solution, we obtained that the relation between viscosity and concentration wasη∝c2.6and the relation between diameter and concentration was d∝c2.3so that we had the relation between diameter and viscosity as d∝η0.87. We obtained d∝η0.8777 by simulating the viscosity and diameter which in accordance with the derived result perfectly.(6) Fabricated nanofibers increased firstly and then decreased by adding inorganic salt Li Br·H2O into PVA solution to change the conductivity.(7) It benefited to decrease solution surface tension by adding a little SDBS. However, along with the increase of SDBS, the surface tension won’t decrease continuously, and the conductivity would increase rapidly so that the morphology of nanofibers would be bad and the diameter of nanofibers would increase.(8) For a certain solution, it exists the best environment humidity that can make the morphology of fabricated products best.We discussed governing equations of charged jets and analyzed criterion of Newtonian and non-Newtonian fluid respectively and their effects on nanofiber morphologies. We found that charged jets had the property of pulsatility. The jet radius oscillates in the instability process. Due to surface tension, necking of the radius results in beads and the relation between distance and period of two beads was obtained.During bubble electrospinning, crimped nanofibers were fabricated when moving bubble films contacted the collector and vibrated. In the paper, we presumed the ruptured bubble membrane as an elastic beam and established vibration governing equations of bubble membrane in accordance with Euler-Bernoulli beam theory and Hamilton least-action principle. And it can be used for industrial production and improvement of stuffing box crimped yarn.Finally, we discussed applications of nanofibers which contain suit design with minimal frictional force, wetting principle of nanofibers and its application, nanometer filter membrane design with silkworm cocoon structure and mass-production of nanofibers. Researches show that:(1) Fractal harmonic law admits minimal friction between moving surface and flow phase when the fractal dimensions of flow phase in Angstrom scale are equal to the fractal dimensions of moving surface in micro scale.(2) The maximum critical volume of wetting spreading was obtained.(3) The structure of silkworm cocoon can be applied to the design of nanofiltration membranes.(4) The mass-production technology of fabrication nanofibers: bubbfil technology, can apply industrial production of nanofibers. And now the output is 16g/h. |
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