Dry adhesion has been a topic of significant academic and industrial interest since the early 2000’s, and a number of different approaches have been explored to create commercial products. Despite an immense effort and a number of extremely impressive academic reports, little progress has been made outside of laboratories due to challenges in the scalability of the approaches. One of the major value propositions of AAI’s approach is the use of a manufacturing approach that is already well known and established: electrospinning. Although it may not be quite a household word yet, electrospinning has a remarkable and rich history dating to pre-industrial times.
Electrospinning fibers ejected from a single needle. Credit: Robert Lamberts, Plant & Food Research, New Zealand.
Electrospinning as a term was largely popularized by the University of Akron’s Professor Darrell Reneker in the early 1990’s, who contributed a number of fundamental insights that brought the field into its modern context. The process itself is essentially identical to any drawing process of fibers from a liquid or a melt. In the simplest case, a fiber-forming material is dissolved into a solvent and drawn out by some pulling force. In the case of electrospinning, the pulling force is an electrical charge, which has a number of advantages that will be highlighted elsewhere. Since the 1990’s, research into electrospinning has undergone a massive renaissance, largely because it is such a simple process, but contains an extreme degree of variability and nuance. It is one of the most efficient ways to produce small diameter polymer fibers. Quite remarkably, under the correct conditions, fibers with diameters as small as 10 nanometers and below can be produced, which is approaching the limit of a single molecule chain.
Despite the significant boom in the field, the fundamentals of electrospinning began to be established in the early 20th century. In 1914, John Zeleny provided the first mathematical attempt to describe the behavior of a fluid under an electrical field. This work was followed by the much celebrated contributions of Sir Geoffrey Ingram Taylor in the 1960’s, which established the mechanistic principles of the distortion of a fluid droplet into a cone prior to the initiation of a fiber jet that are still used today. The cone that forms when a liquid becomes charged by an electric field has aptly been named a “Taylor cone” in honor of his work.
Well before Zeleny and Taylor began to describe the mathematics of a charged liquid drop, a number of scientists and industrialists were investigating the behavior on a phenomenological basis (i.e., trial and error). The first patent for the electrically driven production of fibers dates back to John Francis Cooley in 1900. In the 1930’s and 1940’s, Anton Formal expanded significantly on this and received over 20 patents. Many of the industrial production techniques used today date back to Formal’s original patents. However, the first investigations significantly precede these studies and remarkably date back to before electricity was really understood.
It all starts with a British physician named William Gilbert (more to follow).