The ability to predict mesoscale structure based on the various attributes of nanoparticles, particularly particle size, size distribution, aspect ratio, and chemical functionality, is necessary to understand and potentially tailor the physical response of multi-functional materials. Recently, molecular-scale modeling approaches have indicated that simple estimates of particle shape and local order in a fluid are sufficient to predict various categories of structural order for many convex polyhedral [Damasceno Science 2012; 337 (6093):453-7]. However, these discontinuous nano-scale modeling approaches implicitly assume local constitutive relationships that may introduce considerable error if interfacial interactions or non-local coupling between mechanical fields are present. Extensive experimental investigations have been attempted, but little detail on the fundamental physics of the nanoparticles is possible because of challenges in achieving reproducible properties of an ensemble of individual nanoparticles.
Part 4 of 4 of the epic nanoscale phenomena mini-series, composed during multi-hour travel delays over the holidays... Carbon nanotubes are very exciting materials that are very challenging to use because they really like to group together rather than spreading out. This is because interactions between particles also increase with surface area, which poses a big challenge (this is also part of the reason why electrospun nanofibers can stay together without a binder when used as a dry adhesive!). The challenge is how to separate the tubes without changing their properties too much.
In the field of polymer nanocomposites, there is a great deal of interest in nanoparticles because they can directly interact and influence the behavior of individual polymer chains. The ease of mobility of a polymer chain greatly influences its bulk properties. Generally, we are forced to change the entire structure of the polymer in order to modify something like its use temperature or mechanical properties. Using nanoparticles, we can completely change the behavior of a conventional polymer that is easier to process or prepare that so-called "engineering plastics."
Nanomaterials are so finely divided that they exhibit properties that are intermediate between the macro-scale behavior we are accustomed to, and true molecular-scale behavior. They may show unique properties related to changes in electrical, optical, mechanical, and thermal phenomena (some examples to follow), or may be even more exotic, such as quantum confinement, where the size of a particle is so small that we are altering the configuration and interactions of its atoms and electrons.
Nanoscale phenomena is as nice a place as any to begin a series of non-technical technical articles. After all, it has all the trimmings of remarkable potential, fertile innovation opportunities, challenges in commercialization, and non-intuitive barriers to entry, each deserving of its own consideration. You, me, and everything we generally think of as reality exist on the macroscale. It’s the arena where our senses make sense, where we live our lives and where we can have some intuitive understanding of the world around us. To put it a bit more technically, it’s the arena where things are continuous. Included here are 3 relatively short articles on nanoscale phenomena, which will eventually wrap around to the world of nanofibers, electrospinning, and adhesion that all contribute to the nexus that is Akron Ascent.
AAI is the first company to use electrospinning to produce dry adhesives, which offers the potential for solvent-free, environmentally friendly adhesives that are strong when you need them, but can be easily removed from surfaces without leaving behind a residue or causing damage.produce nanofibers, can be used to produce dry adhesives. Electrospinning is a versatile technique to fabricate nanofibers with finely controlled nanostructures that are useful for a range of properties, including adhesives. Most importantly, electrospinning offers a scalable route to control these structures with a resolution that can typically only be achieved with much more time consuming, batch processes such as lithography.
AAI’s dry adhesive technology is based on the principle of contact splitting, which is a robust and reversible (elastic) mechanism of adhesion commonly exploited by animals such as flies, beetles, spiders, and the most prolific climber of all, the gecko. All surfaces have some attractive force between them arising from weak, inter-molecular forces known as van der Waals (vdW) forces. This force decreases linearly with the size of the contact, but the resulting stress (force divided by area), increases. As a result, a surface made up on a large number of small contact sites will have an immensely larger interaction with a target surface than a smooth one.