Problem Overview:
In the energy industry, efficiency is the keystone to success. Materials that require little to no capital investment or active maintenance and are sustainable for the environment are what drives the products created by companies such as Duracell, Energizer, and Dow Chemical. The study of nanomaterials has emerged into the modern science scene; if a material which is a few nanometers thick has the potential to be stretched into usable dimensions, the application of the material would be cost-effective to all fields of science.
A common technique to stretch materials, namely polymer solutions, into a miniscule thickness is electrospinning. This technique takes a droplet of liquid polymer solution and uses an electrostatic charge to stretch the solution to a thickness of a few nanometers [1]. The design problem for electrospinning is that the nanofibers are typically injected from a syringe and spun through one small stream. Our team wants to solve the problem of making a more efficient electrospinner, starting the path towards the mass production of nanomaterials.
Design Constraints:
When constructing an electrospinner, there are many different factors that must be taken into account in the design of the spinner that can affect the formation of nanofibers. Due to some of these possible design constraints, the nanofibers’ filament diameter and shape can be controlled. Of these constraints there are two types of variables that ultimately determine the effects made on the nanofibers, which are materials and processing.
There are many variables that fall under how the materials used in this experiment will affect how the filament diameter and shape of the nanofibers are established. These variables include anything relative to the polymer and the solution that it comes from. The temperature is affected by the solution viscosity, surface tension, and solvent quality. When the viscosity is increased it affects the width of the nanofibers by increasing it, as well as, preventing more mats from forming on the nanofibers. While the surface tension related to temperature, decreases the nanofibers’ width removing mats as this occurs [3]. Other variables include the chemical composition of the polymer, the polymer’s molecular weight and distribution, and charge density. The net charge density, on the other hand, decreases the width of the filament diameters’ as it increases; also removing mats as the width decreases [3]. Additional variables include the solution concentration and conductivity. Ultimately the material variables not only determine the structure of nanofibers, but also prevent mats from forming on the nanofibers.The processing variables are based on the structure of the electrospinner. The shape and materials used can determine how the nanofibers are formed. The height of the electrospinner can determine the length of how much nanofiber is established as it attracts the fibers from above. The electrode ground distribution also factors into the nanofibers formation because if the possibility of an electric field forming may not be possible. Creating that ground state can be established through different means, as long the charge is not existent. For the design created in this experiment, the distance between the rotating axles can affect how many nanofibers are formed as this permits more beads to form along each string attached to the axles.
Pre-Existing Solutions:
Currently, the most prominently used design in electrospinning is the coaxial electrospinner. In this type of design, the first polymer being used is injected into the middle of a funnel that contains the second polymer being used. These two polymers must be immiscible, and thus, the first polymer remains embedded and surrounded by that of the second [1]. The resulting immiscible mixture is forced through the charged tip of a syringe onto a mat made of a conductive material such as aluminum. This mat is grounded so that the entire system creates an electrical field in which the charged mixture is attracted to the neutral collection mat [2]. Although this design is efficient in producing nanofibers, it is inefficient in the rate of nanofiber production because there can only be one strand of nanofiber being spun at a time. This is due to the limitations imposed by the tiny surface area of the syringe tip. This process is shown in Figure 1 below. The end product from this type of electrospinner is a solid polymer nanofiber surrounded by a shell made of the second type of polymer.
[2] Figure 1: System overview of electrospinning
Another pre-existing solution is the mono-axial electrospinner. This type of electrospinner is identical to that of the coaxial one besides the fact that the mono-axial electrospinner only has the charged syringe, not the inner syringe. This inevitably changes the end product, because with only one syringe, only one polymer can be used, and thus, the product is merely a solid nanofiber that does not include a polymer outer-shell. The reasons for shelled vs unshelled nanofibers are various, and depend largely upon the industrial use for which they are being used.
Design Goal:
The goal of the project will be to design a device that simultaneously conducts electrospinning on multiple jet streams of polymer solution, rather than from one syringe. It is different as it is exponentially more efficient than a typical laboratory’s single syringe setup. The design of this electrospinner allows nanofibers to be made at a faster pace and so reduces the time, and therefore the cost, of creating materials made from these nanofibers. By further improving upon this design, our group hopes to further increase the efficiency and ease of use of this design.
Project Deliverables:
- Redesigned and optimized of an existing electrospinner design made out of K’Nex.
- Scanning electron microscope of nanofibers spun by new electrospinner.
- If time allows, performance test results of capacitor implemented with nanofibers compared to regular capacitor will be recorded and analyzed.
Week 1: Determine design project and member assignments
Week 2: Finish building the original design of the electrospinner
Week 3: Begin working on redesigning the electrospinner (stabilize height and collector)
Week 4: Continue working on redesigning electrospinner (tray mounting)
Week 5: Continue working on redesigning electrospinner (tray design and grounding)
Week 6: Begin creating and testing nanofibers in capacitor/Continue optimizing electrospinner as needed
Week 7: Continue testing nanofibers/optimizing electrospinner design
Week 8: Continue testing nanofibers/optimizing electrospinner design
Week 9: Finish testing and begin analyzing/comparing data from capacitor
Week 10: Presentation
Projected Budget:
Due to the generosity of Drexel University, there are no expected costs for this project. All materials have, or will be, supplied by either the Materials Science and Engineering Department (K’Nex and electrospinner design) or the Chemical Engineering Department (polymer solutions).
Cost of Materials:
- Micro-Bots Series Battlers Building Set (Ace/Stomper) - $21.99
- Polyacrylonitrile 500mg (American Polymer Standards Corporation) - $182
- Polyethylene Oxide 200mg, Anionic Narrow MWD (American Polymer Standards Corporation) - $165
- Dimethylformamide ACS Plus Grade 1 Liter, Amber Glass (Scientific Strategies) - $80.96
References:
[1] C. Burger, B.S. Hsiao, and B. Chu, “Nanofibrous Materials and Their Applications,” Annual Review in Materials Sciences. Vol. 36, pp. 333-368, April 2006.
[2] D. Rosato, "Nanotechnology Driven Electrospun Nanofibers." Omnexus Accelerates Technology and Business Development with Plastics & Elastomers. May 2008.
[3] J. Atchinson, “Process variables for electrospinning” Drexel University, Natural Polymers and Photonics Lab. 2011.
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