Nanotechnology in the World of Paints and Coatings

By Cynthia A. Gosselin, The ChemQuest Group

In 1959, the father of modern nanotechnology, Richard Feynmann, introduced the concept of manipulating matter at the atomic level during his famous Cal Tech lecture entitled “There’s Plenty of Room at the Bottom.”

In 1974, Norio Taniguchi defined nanotechnology as the processing, separation, consolidation, and deformation of materials by one atom or one molecule. By the 1980s, Eric Drexler of the Massachusetts Institute of Technology built on the ideas of Feynmann and Taniguchi to advance the concept of molecular nanotechnology using the idea of the nanoscale assembler, which was proposed as a device able to guide chemical reactions by positioning reactive molecules with atomic precision.

This positioning concept led Sumio Iijima to discover and develop the atomic structure and helical characteristics of multiwall and single-wall carbon nanotubes in 1991.

Fast forward to the 21st century, where nanotechnology has grown exponentially into an exciting and rapidly growing frontier. Nanotechnology has changed the landscape of industrial energy conservation, computer science, biomedicine, electronics, diagnostic biosensors, drug delivery systems, imaging probes, and paints/coatings/adhesives.

In the coatings field, nanoparticles with dimensions between 1 and 100 nanometers (nm) provide the capacity to modify the physical properties of traditional coatings to allow coatings systems to respond to environmental stimuli in a “smart” manner or function as independent coatings with unique characteristics unavailable to less sophisticated barrier coatings.

Nanomaterials, such as nanoparticles, nanotubes, buckyballs, fullerenes, and nano rods measure less than 100 nm in diameter. At this scale, substances operate differently compared to macro scale behavior. Nanotechnology uses structure to control the shape and size at the nanometer scale and then uses these tiny shapes to take advantage of properties made available because of that size.

Nanomaterials and structures can exhibit their unique material properties because of their relatively large surface area that leads to a very high surface-area-to-weight ratio compared to traditional paint additives.
The accidentally discovered carbon dots (C-dots) that are less than 10 nm in diameter are becoming less expensive and more interesting for use in photovoltaic devices, biosensing (i.e., smart coatings), and drug delivery. Graphene (discovered in 2004) led to a carbon-based foundation for almost every engineering pursuit that uses materials. New chemistries allowing metal atoms to be enclosed are creating new, heretofore unknown, organic compounds.

The most dramatic and sophisticated nanotechnology advances have been made in the medical field. However, intriguing innovations have also been made in coatings, paints, and adhesives. Extremely small nanoparticle raw material additions can give paints, varnishes, and adhesives enhanced properties not found with simple barrier chemistries. New advances in processing even allow nanoparticles to combine as stand-alone coatings deposited as thin films with tougher adhesion and surface characteristics. Research is underway to develop extremely fine in-situ nanostructures within coatings to provide enhanced physical and mechanical properties.

A wide variety of enhancements have been made to traditional paints and coatings using nanoparticles. Sometimes these additions can affect the intrinsic physical and chemical baselines of resins and coatings, requiring careful attention to the concentration of these additions to achieve desired improvements without ruining the existing desired characteristics.

Some companies have developed portfolios of nanomaterial additions for paints, but more importantly, also developed corresponding patented processing technologies for incorporating those materials to improve coating properties such as corrosion resistance and self-cleaning characteristics without damaging existing characteristics.

Some promising nanoparticle additions are still in the laboratory stage. A team from Rensselaer Polytechnic Institute1 developed a powerful nanoglue that uses molecular chains to bond surfaces together and can work at very high temperatures. The nanoadhesive is only 1 nm thick—at least 1,000 times thinner than adhesives in current use.

In addition, the nanoadhesive gets stronger as temperature increases. In this case, the normal nanolayer molecular chain of silicon, sulfur, carbon, and hydrogen is anchored at one end by copper and at the other end by silica. This protects the nanolayer chain from rising heat and strengthens the bond as the temperature change rises to increases.

Further work2 demonstrates that the nanomolecular monolayer at the metal/dielectric interface could obtain a fourfold increase in interfacial thermal conductance with this copper-
silica anchored system. This suggests that the interfacial thermal conductance of other material systems could ostensibly be tuned.

This technology may be ideal for bonding together chips as computers and other electronic devices (think Fitbit watches) get smaller and smaller. Even large machinery used in high temperature environments may also benefit from the ability of a nanoadhesive to strengthen as temperatures rise rather than losing adhesive properties at 400 ºC.

Biofouling is the most serious coating problem that maritime industries face today. The solution has economic, environmental and financial implications. Current ship paint technology uses 26–76% by weight of copper oxide additives. Five percent by weight CuO nanocontainers are sufficient to obtain even better antifouling and corrosion results, leading to a dramatic reduction of copper in the paint, resulting in less copper pollution.

The use of Bromosphaerol is also extremely important because it is a natural product compatible with oceanic environments. The self-healing nature of these systems results in a more durable coating. The increase in surface contact angle at the coating surface due to nanomodifications reduces drag resistance of the ship, increasing speed and reducing fuel consumption and air pollution.3
In recent years, many commercial successes have also been realized through a wide variety of nanoparticle technologies. Large, multinational corporations and small, niche coating producers alike are investing in nanotechnology research and enhancing their existing products with clever additions of nanomaterials.

Some examples of successful commercial applications include tungsten oxide nanoparticles in automotive paints to provide electrochromic and photochromic properties. Shading and targeted coloring can be achieved by adding carbon black, zinc, or ferric oxide and silicon or titanium dioxide nanoparticles. Some oxide nanoparticle raw material additions also improve scratch resistance.

Antimicrobial properties where pathogens are killed on contact include nanoparticles of silver, titanium dioxide, and zinc oxide in many coating chemistries used in a wide variety of public buildings and hospitals. Fire-retardant properties can be added to wood coatings through the addition of nanoclays or titanium dioxide nanoparticles.

Enhanced electrostatic spray-painting performance can be achieved through the incorporation of fullerenes or carbon nanotubes, allowing for better deposition and more homogenous flow characteristics.

Smart coatings take significant advantage of nanoparticles. While coatings using nanoadditives are not necessarily smart coatings, many smart coatings have very specific characteristics imparted by nanomaterials. Smart coatings are an improvement over traditional functional coatings in that they exhibit characteristics as a response to external stimuli as opposed to continuously reacting regardless of the environment. Some examples of smart coatings include coatings that respond to the presence of chemicals, volatile organic compounds (VOCs), or carbon emissions and scavenge or otherwise neutralize them.

While many traditional coatings provide inherent corrosion resistance, smart coatings contain nanoadditives that release a corrosion inhibitor only when a corrosive influence is detected. Self-healing coatings contain microcapsules filled with polymeric material that is released only when cracking or other physical damage is detected.

True nanocoatings (as opposed to nanoadditives in “regular” systems) are characterized by very high-volume ratios combined with specific chemical properties tailored for end-use applications. UV-curable coatings exhibiting a high-density homogeneous distribution of micron-sized inorganic fillers filled with 40–60 nm nanoparticles such as zirconium dioxide, boehmite, and silicon dioxide can provide superior scratch resistance, better surface appearance, and superior chemical resistance coveted in many markets. More importantly, these can be applied as thin films.

Another area where nanocoatings are making significant inroads is in managing energy costs in the food manufacturing industry using nanotechnology-based insulation coatings. These patented coatings are based on safe, microsize particles with a nanosize internal architectures mixed into a low-VOC water-based acrylic latex coating.

The nanocomposite is hydrophobic with extremely low thermal conductivity. Manufacturers can easily and efficiently insulate heat processing and cooling equipment and simultaneously protect the equipment from corrosion and mold growth.4

There is worldwide interest in developing new ways to use electricity. Nanotechnology is playing a significant role in enabling solar panels to convert more sunlight into electricity.5 Using nanowires or carbon nanotubes to create three-dimensional nanotextured surfaces that form significantly greater surface area provides more space for reactions for energy generation or storage to make these devices more efficient. Further modification of clear topcoats for solar panels can inhibit dirt and dust pickup, providing a larger clean surface area to be continuously available for reaction regardless of the external environment.

Nanomaterials are used extensively today for improving coating characteristics and service performance, whether as simple additives or as sophisticated stand-alone thin film coatings. Some of these nanocoatings enhance thermal resistance and improve efficient energy generation, while nanoadditives enhance adhesion, corrosion resistance, opacity, durability, cleanabilty, antifogging, antifingerprinting, and UV resistance.

Nanomaterials are no longer only the purview of expensive medical, satellite, or stealth bomber coatings. Rather, these tiny structures, thinner and more complex than the width of a single hair, have infiltrated applications where seemingly ordinary coatings are made stronger, more durable and more resilient with a wide variety of cleverly tailored characteristics for our ever-changing world.

About the Author

Cynthia A. Gosselin, Ph.D, is director at The ChemQuest Group/ChemQuest Technology Institute/ChemQuest Powder Coating Research; cgosselin@chemquest.com; www.chemquest.com.

References

1. Kogutowska, Magdalena. New NanoGlue Likes It Hot. New Scientist. May 17, 2007.
2. O’Brien, P., Shenogin, S., Liu, J. et al. Bonding-induced thermal conductance enhancement at inorganic heterointerfaces using nanomolecular monolayers.
Nature Material 12, 118–122 (2013).
3. G. Kordas, George. Nanotechnology to improve the biofouling and corrosion performance of marine paints: from lab experiments to real tests at sea. International Journal of Physics Research and Applications. July 12, 2019.
4. Nanotechnology Coatings Help Manage Energy Costs from Energy Trends in selected Manufacturing Sectors: Opportunities and challenges for environmental Preferable Energy Outcomes. March 2007. U.S. Environmental Protection Agency.
5. Ahuja, Payal. Nanotechnology Advances for Functional Coatings—R&D Overview. SpecialChem.com. February 20, 2020. (accessed Dec 10, 2021).

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