One of the most common methods of film manufacture is Blown Film Extrusion. The process, by which most commodity and specialized plastic films are made for the packaging industry, involves extrusion of a plastic through a circular die, followed by "bubble-like" expansion. The resulting thin tubular film can be used directly, or slit to form a flat film. Nanoscientists now have found a way to use this very common and efficient industrial technology to potentially solve the problem of fabricating large-area nanocomposite films. Currently, the problems with making thin film assemblies are either the production cost of using complex techniques like wet spinning or the unsatisfactory results of unevenly distributed and lumping nanoparticles within the film. The new bubble film technique results in well-aligned and controlled-density nanowire and carbon nanotubes (CNTs) films over large areas. These findings could finally open the door to affordable and reliable large-scale assembly of nanostructures.
In 2005, researchers in the Netherlands developed the concept of a "molecular printboard" (named for its parallels with a computer motherboard) - a monolayer of host molecules on a solid substrate on which guest molecules can be attached with control over position, binding strength, and binding dynamics. Molecules can be positioned on the printboard using supramolecular contact printing and supramolecular dip-pen nanolithography. In this way, nanoscale patterns can be written and erased on the printboard. This technique, which combines top-down fabrication (lithography) with bottom-up methods (self-assembly), has now been applied to proteins. The resulting "protein printboards", allowing the capture and immobilization of proteins with precise control over specificity, strength and orientation, allows the fabrication of protein chips for applications in proteomics. They will play a major role in unraveling the human protein map, just as special chips were instrumental in mapping human DNA.
Nanofluidic channels, confining and transporting tiny amounts of fluid, are the pipelines that make the cellular activities of organisms possible. For instance, nanoscale channels carry nutrients into cells and waste from cells. Researchers are trying to mimic Nature by constructing nanochannels in order to be able to manipulate single molecules in, predominantly biomedical, applications. Although nanochannels adjustable in size are prevalent in Nature, it is challenging to fabricate them artificially because of conflicting requirements for rigid structural integrity (to prevent collapse) on one hand and reconfigurability of nanometer-sized features on the other (to allow adjustability). Recent work at the University of Michigan addresses these issues and introduces methods to rapidly prototype structurally stable yet reconfigurable nanochannels. By fabricating tuneable elastomeric nanochannels for nanofluidic manipulation, the researchers were able to properly balance the need for flexibility and rigidity.
Current production methods for carbon nanotubes (CNT) result in units with different diameter, length, chirality and electronic properties, all packed together in bundles, and often blended with some amount of amorphous carbon. The separation of nanotubes according to desired properties remains a technical challenge. Especially single-walled carbon nanotube (SWCNT) sorting is a challenge because the composition and chemical properties of SWCNTs of different types are very similar, making conventional separation techniques inefficient. In order to find ways to control nanotube diameter and chirality it would be necessary to monitor nanotube growth. Then, if one knew exactly how to grow nanotubes of different characteristics, one could control their electronic properties because, depending on the way the carbon atoms are arrange around the 'waist' of a nanotube, the electronic properties could vary from metallic to semiconducting. An international group of researchers has demonstrated a novel approach to use nanotubes as reaction cells, enabling them to monitor the birth and growth of carbon nanotubes, and taking some spectacular image of this process.
Back in 1756, the German physicist Johann Gottlob Leidenfrost published a manuscript titled De Aquae Communis Nonnullis Qualitatibus Tractatus ("A Tract About Some Qualities of Common Water") in which he described a phenomenon in which a liquid, in near contact with a mass significantly hotter than its boiling point, produces an insulating vapor layer which keeps that liquid from boiling rapidly. This effect came to be called the "Leidenfrost Effect" and the associated temperature point the "Leidenfrost Temperature." An everyday example of this can be seen in your own kitchen: sprinkle a drop of water in a hot skillet - if the skillet's temperature is at or above the Leidenfrost Temperature, the water skitters across the metal and takes longer to evaporate than it would in a skillet that is hot, but at a temperature below the Leidenfrost point. Researchers in Germany have used this effect for a novel, template-free synthesis and patterning method of nanostructures.
One of the newly emerging areas of semiconductor technology is the field of transparent electronics. These thin-film materials hold the promise of a new class of flexible and transparent electronic components that would be more environmentally benign than current electronics. Being able to print transparent circuits on low-cost, flexible, plastic substrates opens up the possibility of a wide range of new applications, ranging from windshield displays and flexible solar cells to clear toys and artificial skins and even sensor implants. It is likely that such flexible see-through structures will find wide uses in military, biosensing and consumer goods due to the advantages of high transparency and reliable electrical characteristics. However, the emerging transparent electronics technology is facing manufacturing problems: current fabricating processes do not separate the device manufacturing from material synthesis. The transparent electronic materials, which are largely inorganic oxides. are directly deposited on the device substrate under harsh conditions which may cause damage to the existing layer or flexible substrate. The etching of small dimension oxide multilayer is also difficult due to the low selectivity of the etching recipe. New research results demonstrate that nanofabrication techniques could solve these problems.
The promise of revolutionary bottom-up nanotechnology is based on a vision of molecular assembly technologies where nanoscale materials and structures self-assemble to microscale structures and finally to macroscopic devices and products. We are a long way from realizing this vision but researchers are busily laying the foundation for the things to come. Assembling nanoscopic components into macroscopic materials has been an appealing goal but one of the enormous difficulties lies in bridging approximately six orders of magnitude that separate the nanoscale from the macroscopic world. New research at Northwestern University in the U.S. helps to overcomes this difficulty by dividing the assembly process into two manageable sub-steps. First, nanoparticles are assembled into larger, 100 nm-size, spherical building blocks, which are both deformable and "sticky" towards one another. Once assembled, these components "glue" together like pieces of clay to give millimeter or even centimeter-sized structures. The novelty of this technique is both the hierarchical assembly approach (i.e., atoms to nanoparticles to supraspheres to macroscopic materials) and the resulting "soft" structures, which contrast with previously reported hard and brittle nanoparticles assemblies/crystals. This research takes a further step in making nanoscale discoveries relevant to our everyday - macroscopic - world.
Self assembled structures from colloidal particles have many applications in biology, as chemical sensors and as photonic crystals. The control of shape and valency of the colloidal particle is very important since it will determine the 3D lattices of the assembled structure. There have been several prior effort to fabricating particles with complex shapes. Most particles with anisotropic shape are from the simple assembly of spheres or the modification of spherical particles. Interference lithography is one of the few techniques which can provide direct and systematic control over symmetry and volume fraction of the 3D structure. It involves the simple creation of interference patterns in a photoresist systems and subsequent pinch off of the parent structure through a drying process. Researchers at MIT have now presented a new facile and high-yield route for the fabrication of highly nonspherical complex multivalent nanoparticles. This technique exploits the ability of holographic interference lithography to control network topology. These research results could lay the groundwork for establishing and demonstrating control over particle shape in colloidal nanoparticles.