| Electrospun fibers result from an enormous stretching of a fluid jet while the solvent evaporates and the polymer solidifies. The typical path of a single jet of polymer solution, in the electrospinning process, follows the nearly straight electric field lines for a certain distance away from the tip, and then develops a series of electrically driven bending instabilities that cause the path of the jet to explore a volume of space inside a cone shaped envelope.; Two new phenomena were observed during electrospinning a solution of polycaprolactone (PCL) in acetone. First was the dramatic appearance of a fluffy, columnar network of fibers that moved slowly in large loops and long curves. This columnar network is produced under particular conditions when the loops of the wet jet contact each other and become attached, at many points. The name "garland" was given to the columnar network. The second observation was of profuse branching of the primary electrified jet into several smaller jets. Under the right conditions branching and bending occurred together in the same segment. Branching can be profuse, with many long, closely spaced, and rapidly growing branches. Jets with larger diameters tend to have more branches.; Effects of concentration, electrical field, collecting distance, temperature, applied flow rate, spinneret outlet, vapor pressure, and salt to diameter and morphology of electrospun fibers were studied. A small initial fluid jet, less viscous solution, or/and low vapor pressure tended to give smaller fibers. Addition of dissolved salt reduced the number of beads per unit length. The electric field, and applied flow rate were found to have only a small effect on fiber diameter and morphology.; Advantages of electrospun fiber mats, such as the large surface area per unit mass of the electrospun fibers, the ability to conform accurately to the shape of a wound, delivery and release of essential chemicals to stimulate and enhance wound healing, and porosity of the electrospun fiber mat that allows fluids and gases to pass through the mat while keeping infectious agents out for wound dressing were studied. The ability of the electrospinning methods to encapsulate many kinds of useful materials into polymer fibers with a wide range of diameters was demonstrated. Mixtures of polymers, which separated into distinct phases, were electrospun into fibers that contained several very thin fibers of one phase in a matrix of the other phase. |
