A wide range of nano-coatings in a few spray applications

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Easy-to-use nano-coating sprays with optical, electronic, biological properties, etc to cover surfaces. French teams from the Institut Charles Sadron and the Laboratoire de Biomateriaux et Ingenierie Tissulaire, have managed to improve and extend their technique of"layer by layer"deposition. This scientific synergy has led to the development of a very wide range of nano-coatings with new and varied applications that will doubtless be of great interest to industry. Their work was published online on 23 November 2010 on the site of the journal<i>Angewandte Chemie International Edition</i>.

Contact lenses, cars, non-stick saucepans or stickers: numerous objects in our daily lives have coatings with specific functions. Over fifteen years ago, Gero Decher invented a novel method of depositing nano-materials in the form ofthin films. The principle of this technique simply consists in“stacking”, with nanometric precision, layers whose structure and chemical functionalities are controlled by the sequence and nature of the constituents incorporated in the film (polymers, pigments, proteins, particles, etc.). This“layer-by-layer” method makes it possible to produce materials with extremely varied properties. Neither costly nor polluting, this process ranks among the ten most important results in chemistry over the last decade.

Recently, teams of chemists and physical chemistry specialists, headed by Gero Decher and Pierre Schaaf of the Institut Charles Sadron, have succeeded in making this deposition method even more powerful and easy to apply. Initially, the technique required successive dippings in different liquids and long deposition times. Now, using two bottles, the scientists can simultaneously spray two liquids on a surface to be coated. Time saving and logistical advantages are considerable.

Better still, this original method applies to a whole range of nano-coatings, including completely new classes of materials, such as purely inorganic films. The already wide range of applications of these thin films has therefore been further extended. The nano-coatings obtained by these various deposition methods have many applications in materials science: light emitting diodes, fuel cells, photovoltaic cells, anti-corrosion coatings, flexible screens, separation membranes, etc.

Furthermore, the introduction of biologically active molecules (peptides, enzymes, medicines, proteins, DNA, cells, etc.) within these films makes it possible to obtain nano-coatings that have numerous applications in life sciences: biocompatibility of implants, preparation of dressings, tissue engineering, gene transfection, pharmaceutical vectors, bio-sensors, etc. This host of applications is likely to meet industry's objectives to cut production costs, invest in sustainable product development and extend product ranges. In short, this innovative nano-assembly method makes it possible to envisage the elaboration of a large number of (bio)-materials or products that do not yet exist.

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All sprayed at once: Ultrathin coatings made through simultaneous spraying of interacting substances

(PhysOrg.com) -- Coatings functionalize surfaces or protect them from processes such as corrosion, abrasion, and weathering, and may provide an aesthetic appearance—automotive coatings and non-stick frying pans are good examples. Contact lenses, implants, LEDs, or photovoltaic cells require extremely thin coatings.

In the journalAngewandte Chemie, the teams led by Gero Decher at the Institut Charles Sadron in Strasbourg (France) have now introduced a new process for the production of ultrathin coatings that is especially simple, versatile, and suitable for large-scale processes.

A simple yet powerful method for the assembly of nanoscale films is the already well-known layer-by-layer technique. Two mutually interacting species, for example positively and negatively charged polymers, are consecutively adsorbed from solution, forming hybrid thin films through a self-organization process. One major improvement to this method was introduced with the technique of spray-assisted deposition, in which atomized mists of solutions containing each of the two substances are sprayed on asurfacein an alternating fashion. This accelerates the process and facilitates scaling up to industrial levels.

The French–German researchers led by Decher and Pierre Schaaf at the Centre National de la Recherche Scientifique and Jean-Claude Voegel at the Institut National de la Santé et de la Recherche Médicale have now been able to make another substantial improvement to this technique: In“simultaneous spraycoatingof interacting species” (SSCIS), the two complementary components are not applied consecutively, but are simultaneously sprayed against a receiving surface. Depending on the process conditions, the partner substances rapidly form a continuous layer. The thickness of the film is controlled by changing the spraying time and can range from a few nanometers to a few micrometers. This results in highly homogenous coatings that can even possess optical quality.

The one-step process is cheap, robust, user-friendly, and unbelievably versatile. In principle, all pairs of substances that interact with each other, such as inorganic ions of opposite charge, are suitable for use with the simultaneous spray process. It is thus possible to produce films of calcium fluoride (for optical components) or deposits of calcium phosphate (for use in biomaterials).

Interestingly, the new technique also works with pairs that do not produce intact layers when the conventional layer-by-layer process is used. Thus the presented results open up a wealth of new possibilities to produce surfaces with tailored specific functionalities, for example for catalysis, to make implants more biocompatible or for tissue engineering.

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Revealing the secrets of chemical bath deposition

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X-ray absorption near-edge structure (XANES) spectroscopy is well known as a versatile and powerful technique for examining the microstructure of everything from crystalline solids to amorphous materials, even liquids. Its extreme sensitivity also makes it an ideal tool for probing the kinetics of various chemical reactions<i>in situ</i>.

Experimenters utilizing the U.S. Department of Energy Office of Science’s Advanced Photon Source at Argonne recently demonstrated a new wrinkle for XANES that has opened a window on a poorly-understood technique for deposition of materials. These insights will encourage the development of better-controlled and more precise chemical synthesis techniques for semiconductor and other nanomaterial applications, and are valuable as a demonstration of the extension of XANES spectroscopy into other realms of experimentation.

While chemical bath deposition (CBD) is widely used in the laboratory and industry for the creation of thin films and nanostructures for semiconductors and photovoltaics, its actual molecular workings have remained something of a mystery. This has somewhat limited its utility, because precise tailoring of CBD products is not possible without a clear understanding and thus control of CBD mechanics. Scientists from Drexel University and the University of Notre Dame have obtained the first detailed look at how CBD operates at the molecular level, using XANES spectroscopy to witness in situ the formation of zinc oxide nanowires. The work was published in October 2010 inChemistry of Materials.

CBD begins with a water solution with chemical precursors containing the components from which the desired film structure will be formed. But because the precursor chemical species tend to be very dilute within the solution, identifying and isolating them to monitor their activity during the deposition process has been a daunting challenge.“It’s very difficult to find experimental techniques that will allow you to assess the different things that you need to measure,” said principal investigator Jason Baxter of Drexel University.“This has led to some criticism of CBD for being too recipe-based, where it can be difficult to take one set of conditions and say what might happen elsewhere.” XANES proved to be the ideal window into the CBD process.“It gives you very high sensitivity so you can measure species that are very dilute,” Baxter said.“So we were able to look at CBD with a degree of accuracy that people could not achieve before.”

The researchers subjected a solution of zinc nitrate and HMTA (hexamethylenetetramine) to different temperatures and pressures inside a custom-built microreactor device to induce ZnO nanowire growth, observing the reactions with XANES spectroscopy at the Materials Research Collaborative Access Team (MR-CAT) beamline 10-ID at the Advanced Photon Source. Baxter points out a particular advantage of XANES for the current work:“It also has good enough time resolution that we could actually watch the reaction proceeding in time. Every minute we could take a new set of data and look at thekineticsof the reaction.”

One open question the researchers sought to address was the specific role of HMTA in the ZnO CBD process. Previous work had suggested that HMTA might break down into intermediate forms that provided the raw materials for the ZnO film, perhaps even binding to zinc ions in the solution, or that it might act simply as a pH buffer to facilitate the reactions.

This firstin situview afforded by the XANES technique demonstrated that HMTA decomposes slowly under heating, releasing hydroxide ions that react with zinc ions in the formation of ZnO. This slow release of hydroxides also has the effect of minimizing ZnO saturation and thus controlling the solution pH.

“HMTA releases the hydroxide at the appropriate rate, just at the borderline where you’re primarily growing zinc oxide on the substrate with minimal precipitation,” says Baxter.

The team observed the growth of ZnO nanowires from zinc nitrate and HMTA precursors at 90° C after two hours, with typical hexagonal cross-sections and diameters of 300-500 nm.

They also employed principal component analysis (PCA) techniques to obtain quantitative data on the observed species during the CBD process. This showed that the ZnO nanowire growth occurred through direct crystallization from the precursor materials without any long-lived intermediates. The pH buffering provided by the HMTA helps to avoid overabundant precipitation of ZnO in the solution, allowing the controlled growth of the nanowire structures.

These new insights into the mechanisms of CBD will encourage the development of better-controlled and more precise chemical synthesis techniques for semiconductor and other nanomaterial applications.

The work is also valuable as a demonstration of the extension of XANES spectroscopy into other realms.

“I think the more widely useful part of this paper is actually in the application of XANESspectroscopyto a new type of system,” said Baxter.

He and his team plan to extend their work to study other CBD chemistries and processes.“You can actually see what’s happening as it is growing,” he said.“It gives one a lot of information about the process. I think that’s the exciting part.”

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Berkeley lab scientists generate low-cost, hybrid thermoelectrics

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Although climate-controlled car seats don't spring to mind when you think of energy efficiency, the latest technology underpinning this luxury automobile feature is based on thermoelectrics—materials that convert electricity directly into heating or cooling. Conversely, thermoelectrics can also funnel excess heat from energy inefficient systems, such as car engines or power plants, by recovering this 'waste heat' and turning it into electricity. As a result, these materials offer a potentially clean source of energy to reduce fuel consumption and CO2 emissions.

Currently, this thermal energy is converted with high-efficiency, expensive thermoelectricmaterials. In automotive exhaust systems, for example, solid-state thermoelectrics recover waste heat that can result in fuel savings of up to five percent, but their high cost bars them from being used in smaller-scale settings. Boosting these savings through lower-cost materials could make a significant impact in power generation for batteries or electronic components in computers.

Now, Lawrence Berkeley National Laboratory (Berkeley Lab) scientists are tackling this challenge by“changing the budget for thermal energy management,” said Jeff Urban, Deputy Director of the Inorganic Nanostructures Facility at the Molecular Foundry, a nanoscience user facility.

“Historically, high-efficiency thermoelectrics have required high-cost, materials-intensive processing,” said Urban.“By engineering a hybrid of soft and hard materials using straightforward flask chemistry in water, we’ve developed a route that provides respectable efficiency with a low cost to production.”

In their approach, Urban and colleagues constructed a nanoscale composite material by wrapping a polymer that conducts electricity around a nanorod of tellurium—a metal coupled with cadmium in today’s most cost-effective solar cells. This composite material is easily spin cast or printed into a film from a water-based solution. Along with its ease of manufacture, this hybrid material also has a thermoelectric figure of merit thousands of times greater than either the polymer or nanorod alone—a crucial factor in boosting device performance.

“In recent years, we’ve seen tremendous gains in thermoelectric efficiency, but there is a need for low-cost, moderate efficiency materials that are easy to process and pattern over large areas,” said Rachel Segalman, a faculty scientist at Berkeley Lab and professor of Chemical and Biomolecular Engineering at University of California, Berkeley.“We had a lot of intuition about what would work using polymers and nanocrystals, and will now explore materials space to optimize these systems and switch to more earth-abundant materials.”

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Structure of new form of super-hard carbon identified

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(PhysOrg.com) -- An experiment in 2003 formed what was believed to be a new form of carbon, but the findings were controversial. Now two teams of scientists have used different means to identify a three-dimensional network structure called"bct-carbon,"which they say could have been the structure formed in 2003.

Pure carbon exists in a variety of structures, includinggraphiteand diamond. The newstructure, body-centered tetragonal carbon or bct-carbon, is unexpectedly simple and consists of sheets of squares of four carbon atoms each, joined by“short” bonds perpendicular to the sheets. This form of carbon is created when graphite is exposed to high pressure at normal temperatures.

It has been known for nearly 50 years that graphite subjected to cold compression (high pressure at ambient temperatures) undergoes a transformation that is reversible, and in 2003 researchers at Stanford University compressed graphite in a diamond anvil press, while simultaneously obtaining the x-ray diffraction pattern to help them study the bonds within the structure.They found thatwhen the pressure exceeded 17 gigapascals (GPa) (170,000 atmospheres) the carbon atoms in the normally soft graphite formed a material hard enough to crack diamond, but its structure remained unclear.

Now a team of scientists led by Hui-Tian Wang of Nankai University at Tianjin, China, have shown through computer simulations that the super-hard carbon may be at least partly composed of bct-carbon, since this takes the least energy to form. Bct-carbon has a structure part-way between diamond’s cubes of carbon atoms and graphite’s linked sheets ofcarbon atomsin a hexagonal lattice. Bct-carbon consists of sheets of four-atom carbon rings linked together by strong bonds.

The team studied 15 possible structures and found the transparent bct-carbon not only required lower energies to form but that its shear strength is 17 percent greater than diamond’s. If the results are confirmed, this means it may be possible to produce a material stronger than diamond at normal temperatures.

Another group of scientists, including Renata Wentzcovitch of the University of Minnesota and Takashi Miyake from the National Institute of Advanced Industrial Science and Technology in Japan, came to similar conclusions earlier this year, but by a different method. This group analyzed the proposed bct-carbon structure using quantum mechanical simulations. They found bct-carbon was more stable than graphite at 18.6 GPa, and that when mixed with M-carbon it would produce an x-ray diffraction pattern closely matched to that found in 2003. (M-carbon is a structure consisting of layers ofcarbonin rings of five and seven members.)

The paper from Hui-Tian Wang’s team was published in the journalPhysical Review B, while the US/Japan research was reported inPhysical Review Lettersin March this year.

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New high performance insulating plaster developed at Empa

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Empa scientists have developed a high performance plaster which boasts a thermal insulation value three-times better than convention plaster thanks to so-called aerogels. The new material offers an elegant method of renovating historic buildings to save energy without altering their appearances.

Those undertaking the renovation of historical buildings are frequently faced with the challenge of how to improve the thermalinsulationlevels of old structures effectively yet elegantly. To date there has been no method available which offers a technically satisfactory solution to this problem without noticeably changing the appearance of the historic building.

Now, however, researchers from Empa’s Building Technologies Laboratory, working in cooperation with a leading manufacturer of building materials, have developed an aerogel-based high performance insulatingplasterwhich will undergo field trials next year and is expected to be commercially available by 2013. Thanks to its mineral basis, the new plaster is both optically and in application very similar to the original historical building materials, and this makes it ideal for use on old buildings– on internal as well as external surfaces.

The"secret"behind the novel insulating plaster is a so-called aerogel. This substance possesses nanometer-sized pores and consists of 90 to 98 per cent air. These minute pores make aerogels an excellent material for use in the new insulating plaster, lending it a thermal conductivity value of less than 30 mW/m•K which is some two to three times better than that of conventional plaster.

A further advantage of the new plaster is its property of being simultaneously water repellent and permeable to water vapor. The new product is significantly more breathable than conventional plasters, and yet its surface does not become wet. Co-developer Thomas Stahl explains.”The porous structure of the aerogel makes the plaster permeable to water molecules, but for macroscopic water droplets the nano-pores are much to fine.”

The first buildings will be plastered with the new high performance material on a trial basis beginning in mid-2012. The additional cost of this innovative new plaster compared to conventional materials is expected to be between CHF 50 and 100 per square meter, depending on how thickly it is applied.

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Pivoting hooks of graphene's chemical cousin could revolutionize work of electron microscopes

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The single layer material Graphene was the subject of a Nobel prize this year but research led by a team of researchers at the University of Warwick has found molecular hooks on the surface of its close chemical cousin, Graphene Oxide, that will potentially provide massive benefits to researchers using transmission electron microscopes. They could even be used in building molecular scale mechanisms.

The research team, which includes Drs. Jeremy Sloan, Neil Wilson and PhD student Priyanka Pandey from the Department of Physics and Dr. Jon Rourke from the Department of Chemistry together with the groups of Drs. Kazu Suenaga and Zheng Liu from AIST in Japan and Drs. Ian Shannon and Laura Perkins in Birmingham were looking at the possibility of using Graphene as a base to mount single molecules for imaging bytransmission electron microscopy. As Graphene forms an electron transparent sheet just one atom thick it would enable high precision, high contrast imaging of the molecules being studied as well as the study of any interactions they have with the supporting graphene.

While this idea is great in theory, Graphene is actually very difficult to create and manipulate in practice. The researchers therefore turned to Graphene's easier to handle cousin, Graphene Oxide. This choice turned out to be a spectacularly better material as they found extremely useful properties, in the form of ready-made molecular hooks that could make Graphene Oxide the support material of choice for future transmission electron microscopy of any molecule with oxygen on its surface.

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This is a graphic of sample binding to a graphene oxide"hook". Credit: University of Warwick / Nano Letters

Graphene Oxide's name obscures the fact that it is actually a combination of carbon, oxygen and hydrogen. For the most part it still resembles the one atom thin sheet of pure Graphene, but it also has"functional groups"consisting of hydrogen paired with oxygen. These functional groups can bind strongly to molecules with external oxygens making them ideal tethers for researchers wishing to study them by transmission electron microscoscopy.

This feature alone will probably be enough to persuade many researchers to turn to Graphene Oxide as a support for the analysis of a range of molecules by transmission electron microscopy, but the researchers found yet another intriguing property of these handy hooks– the molecules attached to them move and pivot around them.

Dr Jeremy Sloan said:"Under the right conditions thefunctional groupsnot only provide molecular tethers that hold molecules in an exact spot they also allow the molecule to be spun in that position. This opens up a range of new opportunities for the analysis of suchmoleculesbut could also be a useful mechanism for anyone seeking to create molecular sized"machinery"."

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Israel's scientists think big with the very, very small

A material just one atom thick that is stronger than steel but flexes like rubber. A"mini-submarine"that can trick the immune system and deliver a payload of chemotherapy deep inside a tumour.

They sound like the fantasies of science fiction writers, but they are among the discoveries being presented at Nano Israel 2010, a nanotech conference in Tel Aviv that has attracted researchers from across the science world, united by their work with the very, very small.

The 1,500 participants at the two-day meeting which ends on Tuesday include chemists, physicists and medical researchers, all working withtiny structuresaround the thickness of a cell wall.

"We are all working to be able to manipulate molecules at anatomic level,"said Dan Peer, a professor at Tel Aviv University's Cell Research and Immunology Department.

Physicists are developing new materials by removing or adding to existing structures and nano-medical researchers are building new ways to deliver drugs.

Peer is trying to find out how to more effectively target cancer and the inflammation associated with diseases like multiple sclerosis by better directing toxic treatments like chemotherapy.

"Sometimes the drug is there, but it doesn't operate in a targeted manner,"he told AFP.

In such cases, scientists are trying to find ways to build"GPS systems"into the drugs so they travel directly tomalignant cellsor inflammation.

One way of doing that is to attach thecancer treatmentto a vitamin that tumours happily suck up, allowing the medication to penetrate the malignant cells with ease.

"You can potentially create new materials, new vehicles for drugs, like very small bubbles, like mini-submarines, which carry them into the body,"Peer told AFP.

Joseph Kost, a professor at Ben Gurion University of the Negev's chemical engineering department, is working on a technique that delivers chemotherapy drugCisplatininto tumours.

The drug is carried by a tiny vessel through gaps of between 100-1000 nanometres in size, giving scientists a"therapeutic warhead,"he said.

Once inside, researchers irradiate the drug vehicles with ultrasound, causing them to"explode"and disperse the treatment inside the tumour.

Others are looking at ways to trick the body's immune system to prevent it from identifying drug treatments as invading viruses and attacking them.

Elsewhere, physicists like Andre Geim, winner of this year's Nobel Prize for Physics, are usingnanotechnologyto develop new materials with a surprising range of applications.

Geim, a Russian scientist working in Britain, presented his work on graphene, a one-atom-thick slice of graphite that is stiffer than diamond.

"You can imagine you can make a thousand devices out of this graphene,"he told an audience of researchers from 35 countries, whose work could one day produce more efficient conductors and roll-up touchscreens for computers.

Graphene's structure could even allow it to be used for faster DNA sequencing, Geim said.

For Israel, hosting the gathering of nano-researchers is a way of showcasing a sector that the government is trying to foster.

"We see this as a major economic initiative for the future of Israel,"said Barry Breen, a spokesman for Israel's National Nanotechnology Initiative, a government advisory body."It should be a dominant economic engine."

INNI works to match Israel's nanotech researchers with private industry.

A recent project saw Jerusalem-based company 3G Solar work with scientists at Bar Ilan University to develop a solar cell that processes energy in a similar way to photosynthesis in plants.

Aharon Gedanken, a professor of chemistry at Bar Ilan University, is using nanotechnology to develop sterile hospital sheets and robes using a technique called sonochemistry.

The process uses a chemical reaction that produces"microjets,"which throw out nanoparticles of anti-bacterial metals like zinc oxide at"such a high speed that they are embedded in the surface."

The resulting fabric can be washed, even at the hospital standard of 92 degrees Celsius (197.6 degrees Fahrenheit), without losing its anti-bacterial properties.

"The vision of this project is that in the future all the fabrics in a hospital will be anti-bacterial,"he said.

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Radically simple technique developed to grow conducting polymer thin films

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(PhysOrg.com) -- Oil and water don't mix, but add in some nanofibers and all bets are off.

A team of UCLA chemists and engineers has developed a new method for coating large surfaces with nanofiber thin films that are both transparent and electrically conductive. Their method involves the vigorous agitation of water, dense oil and polymer nanofibers. After this solution is sufficiently agitated it spreads over virtually any surface, creating a film.

"The beauty of this method lies in its simplicity and versatility,"said CaliforniaNanoSystemsInstitute (CNSI) researcher Richard B. Kaner, a professor of chemistry and biochemistry and a professor of materials science and engineering at the UCLA Henry Samueli School of Engineering and Applied Science."The materials used are inexpensive and recyclable, the process works on virtually any substrate, it produces a uniform thin film which grows in seconds and the entire thing can be done at room temperature."

Conducting polymers combine the flexibility and toughness of plastics withelectrical properties. They have been proposed for applications ranging from printedelectronic circuitsto supercapacitors but have failed to gain widespread use because of difficulties processing them into films.

"Conducting polymers have enormous potential in electronics, and because this technique works with so many substrates, it can be used in a broad spectrum of applications, includingorganic solar cells, light-emitting diodes, smart glass and sensors,"said Yang Yang, a professor of materials science and engineering at the Samueli School of Engineering and Applied Science and faculty director of the Nano Renewable Energy Center at the CNSI.

One of the potential applications is smart, or switchable, glass that can change between states when an electric current is applied— for example, switching between see-through and opaque states to let light in or block it. The UCLA research group is applying the technique to other nanomaterials in addition to polymer nanofibers in the hopes of expanding the number of available applications.

The team's solution-based technique, published in the peer-reviewed journalProceedings of National Academy of Sciences, was discovered serendipitously when a transparent film of polymer spread up the walls of a container while nanofibers in water were being purified with chloroform.

"What drew me in immediately was the eerie phenomenon of what appeared to be self-propelled fluid flow,"said Julio M. D'Arcy, lead author on thePNASpaper and a senior graduate student in the Kaner's UCLA lab.

"Now I can tell people that I make films in L.A.,"he joked.

When water and oil are mixed, a blend of droplets is formed, creating a water–oil interface that serves as an entry point for trapping polymer nanofibers at liquid–liquid interfaces. As droplets unite, a change in the concentration of blended solids at the water–oil interface leads to a difference in surface tension. Spreading up a glass wall occurs as result of an attempt to reduce the surface-tension difference. Directional fluid flow leads to a continuously conductive thin film comprised of a single monolayer of polymer nanofibers. The uniformity of the film surface is due to the particles being drawn out of the water–oil interface, sandwiched between two fluids of opposing surface tensions.

Development of the technology is occurring in collaboration with Fibron Technologies Inc., with support from the National Science Foundation through a Small Business Technology Transfer grant. Fibron is a small company that has licensed the technology from UCLA. It was founded by Kaner, who serves as chief scientific adviser, and two of his former Ph.D. students— Christina Baker and Henry Tran, who have gone on to take leadership roles in the company.

Fibron's CEO, Christian Behrenbruch, said"working with UCLA to develop this technology has been a win-win. It enables us to access incredibly innovative people, but also, the NSF has helped enable the establishment of a formal and transparent IP releationship with the university. The good news is that this technology is moving rapidly into commercial development."

Other techniques exist for creating thin films of conducting polymers, but each technique tends to work only a limited number of applications, or they are not feasible for scaling up. A method has long been sought which would overcome the limitations of each of the previous methods. The water and oil technique, with a bit of nanotechnology thrown in, might provide just that— a scalable universal method for creating largethin filmsof conducting polymers.

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Researchers create iridescent glass that can reflect UV or infrared light

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(PhysOrg.com) -- Using nanocrystals of cellulose, the main component of pulp and paper, chemistry researchers at the University of British Columbia have created glass films that have applications for energy conservation in building design because of their ability to reflect specific wavelengths of light, such as ultra violet, visible or infrared.

These nanoporous films, described in a paper published in today’s issue ofNature, may also be used in optical filters, sensors, or for molecule separation in the pharmaceutical industry.

“This is the first time that the unique, helical structure of cellulose has been replicated in a mineral,” says Mark MacLachlan, associate professor in the chemistry department at UBC and co-authour of the paper.“The films have many applications and we created them from an exciting new product derived from our wood processing industry right here in British Columbia.”

At the molecular level, the films have the helical structure of nanocrystalline cellulose, a building block of wood pulp, explains MacLachlan.

MacLachlan and PhD student Kevin Shopsowitz, post-doctoral fellow Hao Qi and Wadood Hamad of FPInnovations, stumbled upon this discovery while trying to create a hydrogen storage material.

The UBC researchers mixed the cellulose from the wood pulp with a silica, or glass, precursor and then burned away the cellulose. The resulting glass films are composed of pores, or holes, arranged in a helical structure that resembles a spiral staircase. Each hole is less than 1/10,000th of the diameter of a human hair.

“When Kevin showed me the films and they were red, blue, yellow and green, I knew we’d been able to maintain the helical structure found in thecellulose.”

“The helical organization we produced synthetically mimics the structure of the exoskeletons of some iridescent beetles,” says Shopsowitz.

The pores in the helix give the films a wide range of applications. When certain liquids are added to the film, the liquid gets trapped in the pores and changes the optical properties of the films.

“By functionalizing the pores to make them more selective to particular chemicals, we may be able to develop new sensors that are very sensitive for detecting substances in the environment,” says Shopsowitz.

To reduce the energy needed to cool buildings, windows could be treated with the transparent films that reflect infrared light– the light that heats up a building. Right now, metal particles are often used to do this but they tint the windows brown.

This research was done in partnership with FPInnovations, an organization dedicated to developing new products from the forest sector, and with funding from the Natural Sciences and Engineering Research Council of Canada.

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