Have you ever tried to peel a fresh tomato? Then you probably know that frustrating feeling when you end up with lots of little, mostly triangular pieces of skin. Of course you will also have remembered your grandma's trick to pour hot water over a tomato before skinning it; surprisingly, the skin then comes off easily in just a few large pieces. There are lots of other examples from our daily lives with similarly aggravating experiences: Frustrated by scotch tape that won't peel off the roll in a straight line? Angry at wallpaper that refuses to tear neatly off the wall? Cursing at the price sticker that doesn't come off in one piece? Or you dutifully follow the 'tear along the dotted line' instruction on a re-sealable bag only to be confronted with a tear that is anywhere but on the dotted line. Physicists, mathematicians and materials engineers love these things because it gives them a chance to explain everyday phenomena with impressive looking formulas and diagrams. Wrinkling, folding and crumpling of thin films have been characterized by experiments, theory and numerical simulations. A new study now adds a new element: fracture. The results suggest that the coupling between elasticity, adhesion and fracture, imprinted in a tear shape, can be used to evaluate mechanical properties of thin films and could even be applied at the nanoscale.
Diamonds have been known in India for at least 3000 years and are thought to have been first recognized and mined there. The most familiar usage of diamonds today is as gemstones in jewelry but, apart from being a girl's best friend, it seems that diamonds, especially nanodiamonds, are quickly becoming a scientist's best friend as well. Diamonds are the hardest natural material - the word diamond comes from the Greek term adamas, which means 'invincible' - has the lowest coefficient of thermal conductivity, is electrically insulating, chemically inert, and optically transparent. In nanoparticulate form, diamonds possess an additional property that makes them so interesting for researchers: since they are carbon-based and non-toxic they are a suitable material for drug delivery, drug diagnostics and medical imaging applications. One of the challenges in fabricating nanodiamond coatings and composite materials is the difficulty of controlling the size, texture, and crystalline quality of the diamond particles. Now, researchers in Portugal have demonstrated for the first time the facile fabrication and the conformal coating of nanocrystalline diamond onto silica nanofibers by a two-step method: synthesis of templates on silicon wafer; and coating of the silica fibers with nanocrystalline diamond.
Lithium-ion batteries seem to be everywhere these days. They power most of the electronic devices we carry around with us - cell phones, laptops, MP3 players, digital cameras and so on. They get their name from the lithium ion that moves from the anode to the cathode during discharge and from the cathode to the anode during recharging. Due to their good energy-to-weight ratios, lithium batteries are some of the most energetic rechargeable batteries available today. In terms of weight and size, batteries have become one of the limiting factors in the continuous process of developing smaller and higher performance electronic devices. To meet the demand for batteries having higher energy density and improved cycle characteristics, researchers have been making tremendous efforts to develop new electrode materials or design new structures of electrode materials. Demonstrating the benefits of directed nanostructure-design of electrode materials, Chinese scientists have prepared tin nanoparticles encapsulated in elastic hollow carbon spheres. This tin-based nanocomposite exhibits a very high specific capacity, excellent cycling performance, and therefore shows great potential as anode materials in lithium-ion batteries.
You probably have seen quite a number of research reports on the amazing climbing abilities of geckos. Here at Nanowerk, we ran several Spotlights on this topic, for instance on mimicking gecko toe structures to fabricate super-strong dry adhesives. One demonstration of so-called 'gecko tape' has already been used in building Stickybot, a quadruped robot capable of climbing smooth vertical surfaces, such as glass, acrylic and whiteboard. In addition to the animal kingdom, scientists have started looking at plants to identify biological climbing mechanisms that could be exploited for engineering applications. One obvious candidate is ivy, a climbing woody plant. Researchers now have found that ivy secretes nanoparticles which allow the plant to affix to a surface and play an important role in the plant's climbing capability. This ivy secretion mechanism may inspire new, 'green' methods for synthesizing nanoparticles biologically or new approaches to adhesion mechanisms for mechanical devices.
The past few years have seen tremendous progress in developing and fine-tuning fabrication methods for nanoparticles. An important research direction in nanoparticle synthesis is the expansion from single-component nanoparticles to hybrid nanostructures that possess two or more functional properties thanks to the integration of different materials. Multifunctional nanocarriers are a particularly hot topic in nanomedicine where it is hoped that such particles can significantly enhance the efficacy of many therapeutic and diagnostic protocols. What makes hybrid multicomponent nanostructures so alluring is not only the combination of different functionalities, but also the possibility to independently optimize the dimension and material parameters of the individual components. Apart from their multifunctionality, another advantage of these structures is that they can provide novel functions not available in single-component materials. A recent feature article provides an overview of the synthetic efforts of multicomponent hybrid nanoparticles via high-temperature solution-phase synthesis. The topics include chemical synthesis of multicomponent nanoparticles; characterization of the structural and physical properties, especially the ones arising from the interactions between different components; and potential applications of these multicomponent hybrid nanoparticles.
Understanding and manipulating cellular function at the level of individual molecules is within reach. One of the requirements of single molecule techniques is the ability to follow an individual molecule for sufficiently long times in solution. However, it is a challenge to cope with the effects of Brownian motion (the random motion of small particles suspended in a gas or liquid) on this time scale. To meet this challenge, more recently, biomolecules have been encapsulated inside lipid vesicles, which are themselves tethered to a surface. Now, a novel nanocontainer offers controlled permeability functionality which not only is desirable for single molecule imaging but also is a very important property for micro- and nanodevices and for delivery of drugs or imaging agents in vitro and in vivo.
You have seen the effect: if you splash water on your car it leaves wet areas; if you do this with your freshly polished car the drops just pearl off. Materials scientists are very interested in designing surfaces that allow them to control this effect - called wetting - because it enables them to fabricate things like more comfortable contact lenses, better prosthetics, and self-cleaning materials. The primary measurement to determine wettability is the angle between the solid surface and the surface of a liquid droplet on the solid's surface. For example, a droplet of water on a hydrophobic surface would have a high contact angle, but a liquid spread out on a hydrophilic surface would have a small one. Maintaining the position of a drop of water on a hydrophobic surface (e.g. your newly waxed car) appears to be impossible - it will just move across the surface. Scientists in Israel have managed to fabricate a nanostructured, highly hydrophobic surface that allows them to pin a nearly spherical drop of water in place. A droplet sitting on one class of these substrates did not fall even after the substrate was turned upside-down! An important application for this novel fabrication technique could be as a tool in single-molecule spectroscopy: a water drop, containing molecules to be probed, could be pinned down for an extended time, allowing to spectroscopically probe it for long periods without affecting the properties of molecules, or even just one molecule, dissolved in the water drop.
'Field evaporation' is the phenomenon by which surface atoms are ionized (evaporated) under an applied, extremely high electric field of the order of several volts per nanometer. Electric fields of this magnitude can only be achieved by applying a high field to an extremely sharp needle such as the specimen tip in a Field Ion Microscope. Field evaporation was first reported over 50 years ago and has since developed into the powerful Atom Probe Field Ion Microscopy which is able to reproduce the atomic structure of a piece of material in three dimensions. Today, field evaporation is mainly used for material characterization, and the behavior of nanomaterials at extremely strong electric fields is of great scientific and technological interest. In principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision because of its unique atom-by-atom removal capability. However, detailed structural evolution of nanomaterials during field evaporation has never been directly observed and this limitation has greatly restricted the potential applications of field evaporation as a materials-processing tool. Now, researchers in Beijing have reported the first direct observation of field evaporation phenomena using a transmission electron microscopy (TEM) technique. By conducting in situ TEM field evaporation experiments on individual carbon nanotubes (CNTs), the researchers were able to reveal details about the structural evolution of the nanomaterials via direct observation. Using this technique, they have been able to perform controlled engineering of the CNTs with atomic precision, for example, grinding and shortening of CNTs, shaping of the open ends of CNTs, and opening of CNT caps.