Whether we call them glasses, polymers or ceramics, they take on many shapes and have properties of their own, but they are all materials and can be found throughout our daily lives: in electronics, construction, in the military, in medicine, etc. The development of innovative materials has to involve chemistry. Indeed, the chemist knows the structure of the material and knows how to model it to obtain very precise properties by using organic or mineral synthesis, numerical modeling, a flair for inventiveness and a solid theoretical knowledge.
The following is a description of how Chimie ParisTech chemists continue to invent the materials of tomorrow.
Developing new inorganic materials: used in lasers and biological markers
Lasers... the stuff of dreams for fans of the well-known galactic saga, but they do tend to give physicochemists a hard time. What is a laser? Théodore Maiman succeeded in producing an amplified and perfectly rectilinear light beam from a ruby crystal for the first time in 1960 (which is in fact made of alumina Al2O3 boosted with Cr3+ cations). How? By applying the concept of optical pumping, first proposed by Alfred Kastler at the ENS and for which he won the Nobel Prize in Physics in 1966. The LASER (“Light Amplification by Stimulated Emission of Radiation”) was thus born. Since then, the challenge has been to improve this technology that could be used in so many applications: in the medical sector, lasers are used in ophthalmic surgery (LASIK); in the nuclear field, fusion is often controlled by Megajoule laser; or in microelectronics, where lasers are used to etch most components.
The “Matériaux pour la Photonique et l’Opto-Électronique” (MPO) team, led by Professor Gérard Aka at Chimie ParisTech is working on this very subject. Indeed, lasers emitting in the UV(1) range are complex technologies to put in place because it is a challenge to find materials whose conversion stages make it possible to go from visible to UV. In addition, current gas lasers are too big and not powerful enough over time. “The challenge is global. We have to come up with something solid and compact”, reports Professor Aka. It seems that the solution lies in non-linear materials, which have structural variations at the microscopic or even nanoscopic level. The team was able to achieve visible-UV conversions of up to 12.2% by using a 2.94 nm thick YAB (yttrium alumino-borate) crystal, which is a major achievement in itself.
Which research often leads to dead ends, it is precisely these kinds of victories that sometimes lead to great discoveries. One of the most striking examples is that of aspartame, discovered by G.D. Searle, who was inspired that day to taste a synthetic intermediate taste that was surprisingly sweet.
Researchers from Professor Aka’s team have, admittedly by chance, observed a persistent luminescence in the nanoparticles of oxides they had just synthesized. They considered the possibility of using them as biological markers right away. In the past, radioactive isotopes had been used as cell markers. For example, in positron emission tomography (or PET), a molecule labeled with a radioactive isotope is used and then absorbed by the patient. When decaying (beta plus decay), the molecule produces the positrons necessary for this technology. However, these heavy elements isotopes, even if injected in very low and controlled doses, remain more dangerous than oxide particles. Consequently, patents have been filed for the compound ZnGa2O4: Cr3+. Compatibility studies in biological systems are being carried out in collaboration with the Paris Descartes University to evaluate all the in vivo steps in which this compound has a hand.
Using materials to protect the environment: the example of biocompatible polymers and the containment of nuclear waste
The MPO team is not alone in tackling the issue of materials at school. Researchers from the Chimie Organométallique et de Catalyse pour la Polymérisation (COCP) team, led by Professor Christophe Thomas, is developing eco-compatible synthesis projects from bio-resources to make biodegradable polymers. This is important societal issue for which the challenges are diverse: thinking both about the design of the polymer and its end of life, but also combining the specifications with those of polymers already produced on the market (in terms of properties and especially cost). We already have processes to produce biodegradable polymers! Among those is the Cargill process for PLA (poly-lactic acid), which is used to produce between 700,000 and 800,000 tons of this polymer per year, but requires the use of relatively toxic tin catalysts (read more on these aspects in the Chemistry and the environment article).
The team is focused on sequence control polymerization. It involves synthesizing aliphatic polymers, which are compounds consisting of linear carbon chains or non-aromatic rings, from the opening of cyclic ester monomers. The challenge lies in being able to control the polymer’s microstructure to achieve the desired properties. To that effect, a particular interest is given to the study of the sequence of the monomers (their order) and the tacticity index of the polymer obtained (character R or S of the stereogenic centers).
This theme is present on a European scale, as shown by the biosourced composite synthesis project for the aeronautics and automobile industries. In order to reduce these vehicles’ fuel consumption by lightening them, we are trying to replace their metal parts with polymers.
These polymers are widely used in the nuclear power industry, such as in the clean-up of the premises and equipment of nuclear power plants(2).
Although a renewable energy source itself, nuclear energy, the leading source of electricity in France due to its 58 reactors, is not popular with everyone. Using enriched uranium for nuclear fission does produce a certain amount of radioactive waste that must be treated. The MIM2 (Materials, Interfaces and Soft Matter) team, managed by Min Hui Li, is working on this issue. The most promising lead is trapping waste in clays and oxides. This would allow the long-term management of radioactive waste and heavy metals from the nuclear industry.
Another option being explored is the use of glass as a matrix to confine this waste. Indeed, as early as 1960, France has been using glass as a material for confining the products of fission, because of its flexible structure and its amorphous character. Several research topics started from this. On the one hand, the action of water on glass is simulated by using leaching (solvent extraction) to observe the resistance to corrosion. Indeed, the water flowing in the soil can eventually corrode it and cause leaks of radioactive waste. Additionally, the resistance of the glass to self-irradiation (the radiations it itself emits) is studied.
These two examples illustrate the fact that materials are at the heart of current issues and are strongly related to the environmental and energy issues of the 21st century.
Theoretical chemistry and modeling as fundamental vectors of innovation, but also as privileged support for applied research
With the improvement of software quality and the democratization of computer tools, theoretical chemistry and modeling are emerging as areas of the future. Predictive models, development of methods (using equations) and numerical coding are all projects that contribute to the progress of chemistry and physics. The “Chimie Théorique et Modélisation” (CTM) team is dealing with these issues.
“I’m a chemist first and foremost, which allows me to easily discuss with the experimenter”, says Professor Carlo Adamo. Theoretical chemistry can not only explain the experiment, but also predict its results! We can determine the reaction mechanisms that lead to a given property, or find with certainty the different products of a synthesis before even making it.
One of the team’s research orientation is the modeling of the interaction between light and molecules to explain and predict optical properties based on the excitation phenomenon of molecules. Indeed, many tools have been developed to study the fundamental state, but they are difficult to apply to the molecular excitation process, if at all. It does have many applications, especially in organic dyes. We have a partnership with L’Oréal, who is looking for a reliable tool to predict its products’ color variation. Several studies have been carried out by the team in the subject: the study of the kinetics of the peroxidation of organic molecules, as well as their photo-reactivity and the transfer of charge and protons in photo-induced reactions. This allowed a reliable modeling in the UV-visible spectrum of the organic dyes used by the cosmetics giant.
Under Gilles Gasser’s leadership, the Inorganic Chemical Biology Team (ICB) has developed dynamic phototherapy, yet another application of the excitation of molecules. This therapeutic technique uses non-ionizing radiation, light in this case (for more on this research, read “Chemistry and Health”). To anticipate the performance of photosensitizers, we need to make predictive models of their absorption by biological systems. With this in mind, the team is working in collaboration with the CTM team, which offers TDDFT (“Time-dependent density functional theory”) calculations, which, as the name suggests, is a quantum theory used to study the impact of time-dependent functions (such as magnetic or electric fields) within complex systems. This is a great example of synergy within Chimie ParisTech!
Optical properties are also used in photovoltaics, where the modeling of the interaction between light and molecules can be very interesting. The ultimate goal? “Finding models that are both robust and reliable”.
Metallic materials : focus on innovation
The Structural Metallurgy (MS) team, led by Professor F. Prima, specializes in the design and development of new metallic materials. In collaboration with various industrial partners in the aeronautics (TIMET, SAFRAN, Aubert et Duval) and biomedical (Biotech Dental, LVD Biotech) fields, it is working on the development of new materials with combinations of new properties (resistance/tenacity, high temperature resistance, low elastic module alloys, gradient alloys of properties, etc.), thus opening the way for new fields of application. The team also specializes in the study of the origins of microstructures and in the multi-scale study of microstructure/property relationships in metallic materials. To achieve this, it relies on an experimental park to measure the mechanical properties of materials on site (in deformation) at different scales (MET, MEB) and over a wide range of temperatures. These innovations have resulted in several patents in partnership with various industrial stakeholders and are currently the subject of intense developments aimed at bringing the development of these new materials to industrial applications.
Multiple benefits and perspectives
After this review of Chimie ParisTech’s research on materials, several facts are standing out: on the one hand, this subject is directly related to the other three present in the school. Health, first, through the design of new biomarkers. Energy, by opening new perspectives to the confinement of nuclear waste. And finally, the environment, by reducing fuel consumption by developing biosourced polymers to replace metal auto parts. On the other hand, the synergies within the school, like the one between the teams of Professor Gasser and Professor Adamo, suggest new horizons for research.
Author: Thomas Moragues
Engineering student at Chimie ParisTech - Class of 2020
Glossary
(1) UV laser
A laser emission is performed by exciting atoms using an energy source. That way, electrons pass on electronic levels that are higher in energy. During de-excitation, the electrons fall back to a lower energy level and the laser’s emission wavelength is based on the energy difference between the molecular excitation process and the level of the fall conditions. In the case of a UV laser, this wavelength is between 400 and 800 nm.
(2) N. I. Voronik, V. V. Toropova
Polymer Formulations for “Dry” Decontamination of Equipment and Premises of Nuclear Power Plants, Radiochem. 59,:188-192, 2017.
