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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.

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.

Why geckos? Lots of animals – and even plants – have evolved different methods to move on surfaces. The gecko is unique because it’s heavy. Gecko feet may even mark the upper-bound on natural methods for dry adhesion. Anything heavier is stuck with claws, suction cups, or elevators.

All adhesives in widespread use today can be considered “wet” adhesives.  These materials are typically applied to a surface in a liquid state and achieve intimate contact by flowing along the surface and wetting surface asperities.  To be an effective adhesive, the liquid must be transformed into a solid with high cohesive strength through either a chemical reaction (crosslinking), or in the case of hot melts, by cooling below the melting temperature.

Akron Ascent Innovations is the first company to use electrospinning to produce dry adhesives, which offers the potential for solvent-free, environmentally friendly adhesives that have a remarkable combination of strength and clean, damage-free removability not possible with conventional adhesive technologies.

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.

The first reports on the influence of an electrical charge on a liquid date back to the turn of the 17th century.  At the time, scientists followed the Aristotelian approach and musing about phenomena without any real urge to verify.  William Gilbert was among a new generation of natural philosophers that rejected this Aristotelian approach and instead performed experiments to test prevailing views. 

The concept of a synthetic fiber was first suggested by none other than Robert Hooke, another Englishman of notoriety from the 17th century.  Hooke built some of the earliest telescopes to observe the planets, and was among the first to flip the telescopes around and use them as microscopes to study plant and animal cells.  In fact, he was the one that coined the term “cell” to describe the basic unit of life.  His contribution to the story of electrospinning was in a passing reflection that if “very quick ways of drawing [a synthetic fiber] out into small wires for use could be found,” then artificial silk could be produced.

Dry adhesives are remarkably robust and when incorporated as part of a complete system, can not only displace materials in existing materials, but will open up new frontiers in engineering design that are currently limited by the lack of available materials.

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.