Editorial Feature

Hairy Nanoparticles: What and Why?

A hairy nanoparticle is a hybrid material that contains a polymeric shell and a nanoparticle core. These materials possess many essential characteristics utilized in aircraft, medical, and pharmaceutics. This article discusses the various aspects of hairy nanoparticles and highlights some of the recent advances in this field of research.

Hairy Nanoparticles: What and Why?

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It is crucial to develop novel materials to advance electronics, bioengineering, optics, and many other areas of science. This is why material scientists continuously work on designing new hybrid materials composed of polymers and other components with wide-ranging applications.

Scientists revealed that hairy particles could be dispersed in a polymer matrix to elevate the properties of nanocomposites. Similarly, surface-grafted polymers can also enhance the characteristic feature of composite materials.

Hairy nanoparticles have attracted the attention of scientists owing to their numerous potential applications.

What are Hairy Nanoparticles?

These nanoparticles are also known as polymer brush-drafted particles that consist of a core and a layer of polymer chains. The polymer units are densely bound with each other via covalent bonds, and this layer is present on the surface of the core particle. These hybrid nanostructures exhibit favorable properties of both the polymer as well as the core materials.

A hairy nanoparticle is a class of designer materials. Therefore, these materials have immense flexibility in their design and function. For instance, the core of hairy nanoparticles could be porous, hollow or solid, and are composed of either hard or soft materials.

A hard core comprises metallic or inorganic particles, whereas a soft core consists of synthetic or natural polymers. Generally, the size of these nanoparticles varies greatly, i.e., from a few nanometres to hundreds of nanometres. The core of hairy nanoparticles can be of various shapes, such as cubic, spherical, wire, or rod-like, and sometimes it is designed to take irregular or exotic shapes. 

The polymer brushes can be either random copolymers, homopolymers, mixed homopolymer brushes, molecular bottlebrushes, block copolymers, loop or cyclic polymer brushes, or Janus bicomponent polymer brushes. Furthermore, hairy nanomaterials could be flexible or semiflexible, neutral or charged, and conjugated or nonconjugated.

The main advantage of a hairy nanoparticles is that the grafting density can be controlled, which controls the behavior of hairy nanoparticles present in polymer matrices in turn.

Hairy Nanoparticle Assemblies: The next generation material

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Development of Hairy Nanoparticles

Researchers can develop customized polymer brushes with desirable architectures, controlled molecular weights, and polydispersities. Some of the methods by which hairy nanoparticles are synthesized are discussed below: 

Grafting to

This method involves the grafting of polymers to the surface of the core. The grafting method is carried out by initiating a reaction between a functional group at a specific position on the polymer chain and a complementary group on the core surface. Although this method is straightforward, it yields a weak grafting density.

Grafting from

In this method, the initiator functional group is fixed on the surface of core particles. This step is followed by surface-initiated polymerization in situ, which involves growth in polymer brushes. The main advantage of this method is that it yields a high grafting density. This has been popularly used in controlled polymerization techniques such as ring-opening polymerization, atom transfer radical polymerization, chain-growth condensation polymerization, etc.

In situ synthesis

This method involves in situ synthesis of nanoparticles in polymer micelles, e.g., block copolymer micelles. This approach has been associated with reducing metal salts or crosslinking of the core of the polymer assembly. However, one of the disadvantages of this method is that only very limited types of hairy particles can be produced.

Self-assembling process

Scientists have documented that hairy nanoparticles can self-organize in diverse forms of anisotropic structures. This assembling promotes improvement in the functional properties of materials. Recently, researchers have developed a three-step process for the synthesis of spherical SiO2-hairy nanoparticles, which can control the morphology and chemical properties of a particle. This material comprises the SiO2 core, which is functionalized initially by a short-chain amino-silane acting as an anchor. Following this step, the core is covered by maleaed polybutadiene, a flexible polymer with a lower transient temperature than glass. This method is simple, scalable, and can be utilized to develop different kinds of nanoparticles and polymers.

Application of Hairy Nanoparticles

Hairy nanoparticles have many applications, including photovoltaics, sensors, catalysis, and controlled and triggered drug delivery.

Recently, a new material called preceramic polymer-grafted nanoparticle has been developed by researchers from the Wright-Patterson Air Force Base for use in a new class of aircraft parts.

This new specialized polymeric material has been used to formulate high-performance ceramic fibers and composites. It consists of a chain of polymers on a backbone of silicon and carbon repeats.

The main advantage of this material is that its density is lower than metals, and it could be used in jet engines and hypersonic vehicle components. Additionally, ceramic is resistant to corrosion and wear. Ceramic composites also exhibit high-temperature resistance. Owing to these properties, preceramic polymer-grafted nanoparticles could also be used in propulsion and energy generation systems, medical implants, and chemical processing equipment.

Continue reading: Clinical Applications of Chitosan Nanoparticles.

References and Further Reading

Tripaldi, L. et al. (2021) Silica hairy nanoparticles: a promising material for self-assembling processes. Soft Matter. 41 (17). pp. 9434-9446. Available at: https://doi.org/10.1039/D1SM01085A

Staszewski, T. (2020). Structural Changes in Hairy Nanoparticles—Insights from Molecular Simulations. Journal of Physical Chemistry C.  124 (49). pp. 27118–27129. Available at: https://doi.org/10.1021/acs.jpcc.0c07775

Chen, Y. et al. (2018) Light-enabled reversible self-assembly and tunable optical properties of stable hairy nanoparticles. Proceedings of the National Academy of Sciences. 201714748. Available at: https://dx.doi.org/10.1073/pnas.1714748115

Li, C., Zhao, B. and Zhu, L., (2014) Hairy particles: Theory, synthesis, behavior, and applications. Journal of Polymer Science Part B: Polymer Physics, 52(24), pp.1581-1582. Available at: https://onlinelibrary.wiley.com/doi/pdf/10.1002/polb.23614

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Dr. Priyom Bose

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.

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