Jason Bochinski

Edge electrospinning for high throughput production of quality nanofibers

A novel, simple geometry for high throughput electrospinning from a bowl edge is presented that utilizes a vessel filled with a polymer solution and a concentric cylindrical collector. Successful fiber formation is presented for two different polymer systems with differing solution viscosity and solvent volatility. The process of jet initiation, resultant fiber morphology and fiber production rate are discussed for this unconfined feed approach. Under high voltage initiation, the jets spontaneously form directly on the fluid surface and rearrange along the circumference of the bowl to provide approximately equal spacing between spinning sites. Nanofibers currently produced from bowl electrospinning are identical in quality to those fabricated by traditional needle electrospinning (TNE) with a demonstrated ∼ 40 times increase in the production rate for a single batch of solution due primarily to the presence of many simultaneous jets. In the bowl electrospinning geometry, the electric field pattern and subsequent effective feed rate are very similar to those parameters found under optimized TNE experiments. Consequently, the electrospinning process per jet is directly analogous to that in TNE and thereby results in the same quality of nanofibers.

Dynamics within Alkylsiloxane Self-Assembled Monolayers Studied by Sensitive Dielectric Spectroscopy

Self-assembled monolayers are a ubiquitous laboratory tool and have been the subject of many experimental investigations which have primarily focused on static properties of full coverage monolayers, with the maximum density and ordering possible. In this work, dynamics within low density, planar siloxane self-assembled monolayers are studied utilizing highly sensitive dielectric spectroscopy. Dilute, disordered films were intentionally fabricated in order to study the widest range of possible motions. At low coverage, an interacting relaxation is observed, which has similar dynamics to polyethylene-like glass transitions observed in phase-segregated side-chain polymers, despite the rigidity of the substrate and the constraint of ethyl groups in relatively short chains. As density is increased, a second local relaxation, previously observed in three-dimensional SAMs and associated with rotation within a small segment of the alkyl chain, is also observed.

In situ curing of liquid epoxy via gold-nanoparticle mediated photothermal heating

Metal nanoparticles incorporated at low concentration into epoxy systems enable in situ curing via photothermal heating. In the process of nanoparticle-mediated photothermal heating, light interacts specifically with particles embedded within a liquid or solid material and this energy is transformed into heat, resulting in significant temperature increase local to each particle with minimal warming of surroundings. The ability to use such internal heating to transform the mechanical properties of a material (e.g., from liquid to rigid solid) without application of damaging heat to the surrounding environment represents a powerful tool for a variety of scientific applications, particularly within the biomedical sector. Uniform particle dispersion is achieved by placing the nanoparticles within solvent miscible with the desired epoxy resin, demonstrating a strategy utilizable for a wide range of materials without requiring chemical modification of the particles or epoxy. Mechanical and thermal properties (storage modulus, T g, and degradation behavior) of the cured epoxy are equivalent to those obtained under traditional heating methods. Selective curing of a shape is demonstrated within a liquid bath of epoxy, where the solid form is generated by rastering a spatially confined, photothermal-driving light beam. The non-irradiated regions are largely unaffected and the solid part is easily removed from the remaining liquid. Temperature profiles showing minimal heating outside the irradiated zone are presented and discussed.

Unconfined, melt edge electrospinning from multiple, spontaneous, self-organized polymer jets

Commercial grade polyethylene is melt electrospun from a thin film of unconfined molten polymer on a heated, electrically-grounded plate. Under the influence of an applied electric field, the melt spontaneously forms fingering perturbations at the plate edge which then evolve into emitting fiber-forming jets. Jet-to-jet spacing (∼5mm), which is dependent on the applied voltage amplitude, is in agreement with estimates from a simple theoretical treatment. The broad applicability of the approach is verified by spinning a second polymer —polycaprolactone. In both cases, the fabricated fibers are similar in quality to those obtained under needle melt electrospinning; however for this method, there are no nozzles to clog and an enhanced production rate up to 80mgmin �1 is achieved from approximately 20–25 simultaneous parallel jets. The process of jet formation, effective flow rates, cone-jet diameters, as well as limits on jet density and differences with polymer type are compared with theoretical models. This particular approach allows facile, high throughput micro- and nano-fiber formation from a wide variety of thermoplastics and other high viscosity fluids without the use of solvents or the persistent issues of clogging and pumping that hamper traditional methods, resulting in mechanically strong meso-scale fibers highly desirable for industrial applications.