Gas jet process for production of sub-micron fibers

A new, simple, and effective method was developed for production of fibers from polymer solutions with diameters ranging from a few tens of nanometers to a few micrometers. The process, termed gas jet nanofibers (GJF), bears several similarities and contrasts with electrospinning and melt-blowing processes. The method capitalizes on a high velocity expanding gas jet to turn polymer solutions streaming from nozzles into fibers with smooth or wrinkled fiber surface morphology and with core-shell and side-by-side arrangements. The polymer solution is brought in contact with the gas jet on a flat surface, at the tip of a circular needle, and on the surface a pendant drop. The fiber diameter bears relationship with capillary number of the liquid jet and polymer concentration in the solution. Several levels of fiber conglutination are observed as function of the collection distance from the nozzle.;The dynamics of the formation of the fiber in the GJF process was inferred from the high speed video images of the liquid jet emanating from the nozzles. The fiber diameter attenuation was found to originate from flapping and bending instabilities and concurrent solvent evaporation. The fiber is initiated by a single liquid jet formed as the liquid emerges from each nozzle configuration. The liquid jets of diameters from around 40 mum to 600 mum are attenuated to the sub-micrometer level within a small distance from the point of liquid-gas contact.;The process adaptability was demonstrated with several case studies. First, the production of compound fibers with core-shell and side-by-side configurations was studied for pair of immiscible polymers. Polyvinyl acetate (PVAc), polyethylene oxide (PEO), and polyvinyl pyrrolidone (PVP) were used to create compound fibers with different sizes and configurations. Second, the production of bi-component nanofibers with controlled morphology produced from homogeneous solutions of an immiscible pair of polymers in a miscible pair of solvents was developed. The approach is based on evaporation rates of selected solvents and solvent-evaporation-induced phase separation of the polymers during stretching of the liquid jets by the gas flow. The approach yielded nanofibers from blends of polyvinylacetate and polyvinylpyrrolidone with diameters below 500 nm exhibiting several morphological forms after phase separation of the polymers including interpenetrating, bi-lobal, and core-shell.;The gas jet method was also used to produce carbon fibers with diameters ranging from 100 nm to several micrometers from mesophase pitch by using a patented nozzle system. The process is based on force exerted by coaxial hot jets of air on the molten mesophase pitch in the nozzle. The dynamics of the gas jet and the formation of the fibers were studied by using computational fluid dynamics (CFD) models. It was learned that fibers are formed from a combination of ripples and growth of wave perturbations in the interphase between the fiber precursor and air due to the competition between the forces originated from aerodynamics, surface tension, and inertia.