The domain of the infinitely small

The domain of the infinitely small

By AVICENN Team – Last Modified February 2023

What infinitely small are we talking about?

Nanotechnology: making and manipulating nano-objects

Nanotechnology refers to processes for manufacturing and/or manipulating structures at the nanometric (nm) scale, that of the infinitely small:

We are located at molecular and atomic scales. For information :

• some viruses are a hundred nm in diameter
• human DNA is 2 nm wide,
• and a carbon or hydrogen atom measures 0,1 nm

This is 1974 when the term “nanotechnology” appeared, which began to develop in the 1980s, with the creation of the scanning tunneling microscope then from atomic force microscope.

What is a nano-object?

Nano-objects or nanoparticles are like nano-grains but which can have very different shapes (threads, plates, particles or nanoporous substances) and which are generally grouped together, in particular in powder form.

From a chemical point of view, to simplify they can be considered as different substances from “classic” substances, different from two points of view:

• Firstly at waist level, because these particles are of very small size, since we are at the nanometric scale
• on the other hand, nanoparticles and nanomaterials have different properties those of conventional materials: they can change color or become more conductive, more solid, more photocatalytic, for example.

Manufactured nanomaterials

The engineered nanomaterials refer to man-made nanoscale materials; they have “extraordinary” properties (in the proper sense of the term) with respect to structured materials at the micro- or macroscopic scale.

Ils are different :

• … natural nanoparticles found in dust from erosion or volcanic eruption, or even in sea spray, for example. Many viruses are also nano-sized.
• … as well as nanoparticles say "incidental" which are produced "involuntarily" and are present:
  • in Mayan paintings, Roman glassware (Lycurgus cup) or in XNUMXth century Damascus swords, in wood combustion smoke, etc. well before the industrial period
  • and more widely in industrial fumes or those emanating from diesel engines and other so-called “ultra-fine” particles¹See for example the participatory project NanoEnvi, funded by the CNRS, led by the Geosciences Environment Toulouse laboratory (GET-CNRS/Toulouse III University – Paul Sabatier/IRD/CNES) of the Midi-Pyrénées Observatory (OMP), bringing together researchers in magnetism from the environment, sociology and physics from the Aerology Laboratory (LA – CNRS/ Toulouse III University – Paul Sabatier) and the Physics and Chemistry of Nano-objects Laboratory (LPCNO – CNRS/ Toulouse III University – Paul Sabatier/INSA). Mélina Macouin, CNRS researcher at the Toulouse Environmental Geosciences Laboratory (GET-OMP, CNES/CNRS/IRD/UT3 – Paul Sabatier), toasters or ovens for example, or by the wear of tires and brake pads²See for example:
    In French :
    - Measures should be taken to reduce particulate emissions from wear of automotive parts and road surfaces, OECD, December 2020
    - Air pollution: new knowledge on ambient air particles and the impact of road traffic, ANSES, July 16, 2019
    - Nano-safety: Brake pad emissions under scrutiny, CEA Liten, June 11, 2019
    - Particle emissions from the brakes: a future health scandal?, Science & Future, September 21, 2018
    
    In English :
    - Brake dust exposure exacerbates inflammation and transiently compromises phagocytosis in macrophages, Selley M et al., Metallomics 2020
    - Pollution warning over car tire and brake dust, BBC, 11 July 2019, etc..

Despite their differences, engineered nanomaterials and ultrafine particles (UFPs) have many things in common, especially in terms of the challenges they face. tools to detect, measure and characterize them or to assess their risks³See Nanomaterials Versus Ambient Ultrafine Particles: An Opportunity to Exchange Toxicology Knowledge, Stone V et al., Environmental Health Perspectives, 125 (10), 2017.

If it already exists several hundred different substances marketed at the nanoscale (more than 300 are registered in the French register r-nano and also listed on the European Nanomaterials Observatory), the vast majority of nanomaterials used by industry belong to the following four categories :

• the nano-silver
• the carbon nanotubes
• the titanium dioxide nanoparticles
• the nanosilica.

They most commonly come in the form of ultra-fine powders (in creams, lotions, sprays, dressings…), to which humans or the environment can be directly exposed.

They can be embedded in solid materials (such as carbon nanotubes in bicycle frames), in which case they do not come into direct contact with humans or the environment during their use, but potentially during their production or during the degradation of the products at the end of their life cycle.

Specific properties

Indeed, the interest and the growing development of nanomaterials are explained by the specific properties that it is possible to create by modifying the material at the nanometric scale, in particular the size or other physico-chemical characteristics materials.

At the nanoscale, matter deploys new or more marked properties, in particular due to the small size of nanomaterials which gives them a larger reaction surface than the same non-nanometric material. Why ? Because the proportion of atoms on the surface (compared to the volume) is greater than for larger materials, allowing greater exchanges and interactions with their environment⁴See for example:
- Nanoparticles: Is Toxicity a Concern? DR, Rao P. EJIFCC, December 2011
- Reactivity of inorganic nanoparticles in biological environments: insights into nanotoxicity mechanisms. Casals E, Gonzalez E, Puntes VF, Journal of Physics D: Applied Physics, 2012.

Two images to understand this “ size effect "

• visualize the surface covered by the contents of a spoonful of cocoa powder spilled on the table: it is equivalent to the surface of an entire bar of chocolate
• cocoa powder melts faster in milk than large squares of chocolate

Similarly, nanomaterials are more “reactive” than non-nano materials.

At the industrial level, these new properties of nanomaterials are perceived as opportunities in many fields of application, hence the growing number of patents each year.⁵See for example:
- Nanotechnology Published Patent Applications in USPTO: Number and Annual Growth Rate during the Past 20 Years, StatNano, December 30, 2020
- Nanomaterials with the Highest Number of Granted Patents in USPTO, StatNano, November 25, 2020
- Nanotechnology patents in USPTO (Patent), StatNano (accessed November 2020).

A sunscreen containing titanium dioxide nanoparticles (TiO₂) is more transparent than a "classic" cream whose TiO₂ is not nano, thus avoiding white deposits on the skin, which brands use as selling points.

New properties, new markets

Most nanoproducts on the market today offer advantages due to the addition of nanoparticle powders which give them new properties, with various advantages:

• elimination of bacteria (and bad smells) for the nanosilver, used in textiles, dressings, disinfectant sprays, coatings for fridges, keyboards, food packaging, etc.
• resistance and lightness for carbon nanotubes, which constitute a major asset in particular for the transport industry
• Sun screen ou photo-catalytic effect (anti pollution) for the titanium dioxide nanoparticles which, depending on their effect, can be used in sunscreens or cements
• anti-caking and therefore thinning effect for nanosilica for food use, used in powdered sugars, table salts, etc.
• catalytic effect (triggering of chemical reactions) for metallic nanoparticles, with applications in the field of health
• swerve " antifog " obtained by a lamination of gold nanoparticles and titanium dioxide
• ...