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METHOD AND DEVICE FOR GENERATING CONTINUOUS FIBRES HAVING A NANOSCALE DIAMETER AND NANOSCALE FIBRES GENERATED
US2019032248
The present invention describes a method for generating long fibers having a nanoscale diameter by means of the combined application of a gas jet and laser radiation. The invention also relates to the nanoscale fibers generated by said method, as well as a device suitable for the implementation thereof.
- This technique allows to produce separate, solid, continuous, and non-porous fibres with controlled diameters, in the nanoscale range, and indefinitely long lengths. <br> - The nanofibers obtained are advantageously solid, continuous, and non-porous with diameters between 1 and 900 nm and lengths from 1 cm and 4 x 10^6 m. <br> - The fibers obtained are flexible and completely separated so they can be ordered, aligned and woven. <br> - There are no restrictions regarding the chemical composition of the product on the grounds of incompatibilities of the precursors. <p> - The fibers obtained can be used in the production of fire-resistant fabrics, as a polymer reinforcement for manufacturing composites, as a base material for different types of cells in tissue engineering (such us in the regeneration of bone, mucosa, skin or cartilage) or for manufacturing active bifunctional and recyclable filters. <p> - The laser beam heating process, as well as the gas jet cooling process, take place much more quickly than in the melt blowing method. <br> - Heating and cooling processes are much faster than breaking flows, allowing heating to be brought up to higher temperatures without the flow breaking due to the effect of instabilities or capillary forces. <br> - Nanoscale diameters can be attained without the filament breaking or cristallizing: the fluid filament attains lower viscosity compared to other methods, meaning the elongation takes place very quickly, and the diameter of the prefom, made made from a precursor material, can accordingly be reduced by factors of less than 1/1000.
This method is based on the micromelting of a preform, made from a precursor material, with a high-power laser to generate a microfilament made of molten material. At the same time, a gas jet fed at a high speed and in a coaxial manner with respect to the microfilament, causes the elongation and cooling thereof. <p>
The optimal viscosity to favour drawing of the preform made from a precursor material, must be low enough so as to allow a rapid flow of uniaxial elongation of the preform, by the entraining effect caused by the process gas. At the same time, viscosity must be kept high enough so that the surface tension does not cause the filament to break due to capillary forces. <p>
The precursor material is preferably an inorganic glass, a polymer, a ceramic material, a metal oxide, with a temperature varying rheological behaviour that, when heated by laser radiation, reaches a suitable viscosity to surface tension ratio. The precursor material may be in liquid, semi-solid or solid state, and be selected from the group of silica, phosphate glass, and polymers such as polylactic acid (PLA) or polycaprolactone (PCL). <p>
FIG. 1 schematically depicts the cross-section of the processing head (2) of a device, according to an embodiment of our invention, for injecting gas (4) in a coaxial manner (8) with respect to the flow of precursor material (1). Also depicting two laser beams (6 and 7) that irradiate, from opposite directions, the preform made from the precursor material in the processing area (3) and obtaining a microfilament. Lastly, the reduction of the diameter of the preform in the processing area (5) until producing a continuous nanoscale fiber (9) at the outlet, is also schematically shown. <p>
FIG. 2 schematically depicts two plan and elevational views of the configuration of the optical elements required to carry out the experimental assembly of a device according to an embodiment of our invention. In the diagram, two laser radiation beams (10) and (11) aim at respective total reflection mirrors (12) and (13). The propagation of both beams, (16) and (17), is modified by means of respective identical optical instruments (18) and (19) to achieve desired irradiance on the preform (14). Finally, the preform emerging from the processing head (15) and the processing area, irradiated by the two beams in opposite directions, where transformation of the preform made from the precursor into a nanoscale continuous fiber (20) takes place.