NINA KREISIn a world invisible to the naked eye, tiny particles detect substances, minuscule capsules carry medication to specific points in the body, and tubes tens of thousands of times smaller than a hair strand are involved in the recovery of polluted zones. The universe of nanometric scale materials is becoming increasingly broad, revealing a growing diversity of applications, and enabling the construction of increasingly small devices.
The talks at the second meeting of the Cycle of Conferences of the International Year of Chemistry, held in São Paulo on May 12, offered a tour of this landscape that is normally invisible, but also showed that this is not only mysterious for lay people: “The chemical engineers that use the new materials don’t know a thing about chemistry,” joked the conference coordinator, Rosario Bretas, from the Federal University of São Carlos. An engineer, she too tends to regard chemistry as a problem. “We have to know how much to use of each element and what the ideal conditions are for useful nanostructures to form,” she told us, stressing the importance of the presentations that were to follow, by the chemists Fernando Galembeck and Oswaldo Alves, from the State University of Campinas (Unicamp), and Henrique Toma, from the University of São Paulo (USP). The cycle, which goes until November, is an initiative of FAPESP and the Brazilian Society of Chemistry as part of the celebration of the International Year of Chemistry, the theme of which is Chemistry: our life, our future, promoted jointly by the International Union of Pure and Applied Chemistry (IUPAC) and Unesco.
Fernando Galembeck stressed the need to acknowledge that science is now undergoing a number of obstacles. “Some day-to-day topics, such attrition and electrostatics, are not very well understood by the scientists in any area, due to no attention being paid to the chemical phenomena involved,” he said provokingly. According to him, this ignorance is what allows explosions caused by electrostatic discharges to occur, such as that which, in 2003, destroyed the Satellite Launch Vehicle at the Alcantara base in the Maranhão state. “We don’t know what keeps the droplets together to make clouds! As these droplets have a charge, they should be repelling each other.”
Galembeck’s studies have shown that surfaces have unexpected electrical properties caused by their chemical nanostructure. To make use of this knowledge, one must keep an open mind and avoid many established canons. A core phenomenon, he showed, are the patterns of electrical charge distribution on surfaces. “I am yet to find an electrically smooth surface.” Based on this, the researcher has created and successfully applied a new model, in which water ions lend a charge to the surface of materials, changing their properties. According to Galembeck, the water molecules penetrate any material. The first articles took a long time to be accepted, perhaps due to the fact that they are very new, but today experts are welcoming them.
The effect of electricity on water is clearly illustrated by a video of drops that fall from an electrified needle. At first, the drops are rounded and drip slowly. As the voltage becomes more negative, the pace increases fast and the drops become longer, until they form a continuous filament. “The atmosphere is a reservoir of charges and the transfer of charges eliminates the superficial tension that maintains the drop’s structure,” he explained. The important thing is to see how, in order to advance in the development of new materials, one must go back to the roots of knowledge without it becoming hierarchical. “Old chemistry theories are what has allowed us to put together this theoretical progress,” summarizes Galembeck, who is now conducting experiments to capture electric energy from the atmosphere. On a small scale, because, as he joked, he is yet to get the financing required to capture lightning during storms.
Self-organizing
The importance of electron behavior, the basis of electricity and of electronics, was recurrent in the talks by the researchers. However, beyond electricity, it is indispensable to understand all the parameters that affect the properties of the compounds, which sometimes form spontaneously. In search of innovation, Oswaldo Alves puts himself in the position of an observer of natural phenomena to detect the complexities that may appear in nanostructured materials. In ordered porous materials, for example, he has shown that temperature affects the characteristic of the walls supporting the structure. Temperatures equal to or higher than 800 degrees Celsius (°C) cause this structure to collapse.
The construction of nanomaterials is not new: “Building quantum dots in Brazil was already feasible 20 years ago,” Alves states, in reference to nanocrystals, which are semiconductors also known as quantum dots. They have an endless number of uses, in telecommunication and in optical equipment, for example. The terminology used by the experts is hair-raising, but, in practice, it is sufficient to work with specific building blocks and to supply the ideal conditions, such as temperature, for a structure with the desired morphology and size, to form.
Nanotubes are an emblematic case. Generally made from carbon, as is the case of graphene sheets, they consist of a rolled-up layer of carbon atoms. “However, graphene is a semiconductor,” recalled the researcher, stressing that the different uses call for materials with specific properties. In his laboratory, he has managed to build totally inorganic (carbon-free) nanotubes made of vanadate or titanate, and nanosticks of molybdenum trioxide, which, when examined under an ultrapowerful microscope, look like popsicle sticks.
EDUARDO CESAROswaldo Alves, Henrique Toma and Fernando Galembeck EDUARDO CESAR
When he made spheres of molybdenum sulfide, he noticed that they looked odd. The solution was using a FIB (focused ion beam) microscope, which enables manipulating the particles. “The beam spread the spheres as if they were a game of billiards,” he compared. With this tool, it was possible to cut one of the spheres and to find out that it was hollow. “After design and construction comes the application, which is a different story.” The hollow nanospheres can be used as nanocarriers, for instance, to carry medication to specific sites in the body. Another unexpected apparition occurred when silver vanadate nanofilaments were being made. These can have antibacterial property due to their silver nanoparticles. Under the microscope, these minuscule particles seemed familiar: they looked like Mickey Mouse. Before doubting the seriousness of the research group, it must be made clear that the researchers wasted no time trying to build characters from comic books invisible to the naked eye. “This self-organization phenomenon was not intentional, but the eye had to be ready to see it,” he told us.
For him, developing new materials may involve putting new clothing on old, well-known compounds, and then to make intelligent use of the self-organization phenomenon, especially when it comes to applications. “If the nanomaterial is highly exotic, it lacks an epidemiological history or nanotoxicological data. Therefore, it becomes harder to get approval for clinical use, for instance.”
Piece by piece
Also in search of useful novelties, Henrique Toma, from USP, uses an approach that is closer to that of a model builder. “We try to make the components work in synch,” he described. This is a specialty known as supramolecular chemistry. What he regards as a dream is to transform day-to-day chemistry into chemistry that is better ordered, controlling the characteristics and making molecules really intelligent.
He is aware that he lives in a new world, in which the molecule per se has turned into a material and invisible structures move the economy. One example of this are gold films one billionth of a meter thick, so fine that the light that passes through them can interact with the surface electrons of the two surfaces. The angle at which the light starts resonating with the electrons and is totally absorbed allows one to detect material on the surface with dimensions that are far smaller than those of a grain of sand. This tool is being used in the laboratory to monitor DNA and to study how it interacts with drugs and other chemical agents. With this kind of technique, Toma is working toward developing devices for medicine and for energy conversion, as well as sensors that are efficient and that cost almost nothing for food, beverages and pharmaceutical products, for example. The most important client for innovations produced in his laboratory is Petrobras, which requires a range of nanomaterials, such as catalysts and detectors of pollutants to use in the field.
The transfer of electrons, which is essential for all the compound-forming processes, can even give rise to artistic manifestations, as Toma has shown. His research group has developed pigments with special organic molecules and metal ions that, when sprinkled with or dunked in a solution with nanoferrates, reveal an image by means of electron transfers between the substances. “It used to be the opening of chemistry shows; students would dunk the filter paper in liquid and suddenly the Brazilian flag would appear,” he told us. The process gave rise to the image that Toma made in honor of the 1983 Nobel Prize, awarded to an American, Henry Taube, the first person to propose an electron transfer model. “It’s a summary of the entire theory that led him to win the prize.” He does not know how Taube interpreted the painting when he got it, but the USP researcher says that it represents all the important elements in the model developed by the American scientist. It is a good example of basic principles of chemistry giving rise to unexpected phenomena, the playful element being something of a bonus.
The three speakers made it clear that this playful side permeates the study of chemistry. The investigation of chemical phenomena, of the formation of compounds and the observation of their behavior is, for them, an ongoing source of fascination. Galembeck extended to students and those who are curious about chemistry the invitation of Jean-Marie Lehn, a Frenchman and the Nobel laureate for Chemistry in 1987, at the opening of the International Year of Chemistry: “The book of chemistry is yet to be written, the music of chemistry is yet to be composed. I invite you to take part in its creation.”
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