For decades, high-density, end-tethered polymers that form polymer brushes have been investigated to determine their characteristics and potential for commercial applications.
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Polymer bristles consist of densely connected polymer chains that can adhere to a wide range of materials and surfaces. This article focuses on the fundamentals of polymer brushes as well as their applications in nanotechnology.
What are Polymer Brushes?
Polymer brushes are made up of continuous monomers that are attached to an interface by one chain link at a sufficiently high density for the polymers to extend outward from the substrate.
These brushes may consist of negatively charged anionic or positively charged cationic polyelectrolytes, macromolecules, or polymer chains containing various types of monomers.
Commercial manufacturing, as well as research and development of bioinspired nanofabricated lubricants, anti-fouling agents, and antibacterial substrates, relies heavily on the utilization of polymeric brushes.
Synthesis Methods of Polymer Brushes
Physio-sorption or covalent adhesion is typically utilized to create polymer brushes. In contrast to covalent attachment, physio-sorption is thermally and solvent-instable.
The popular techniques of covalent attachment for synthesizing polymer brushes include ''grafting to'' and ''grafting from''. The process of ''grafting'' involves the attachment of prefabricated polymer chains to a surface. However, this method frequently results in poor grafting density (substrate penetration) and thin films.
As a result of these constraints, the ''grafting from'' method has become the method of choice for the synthetic production of polymer brushes. This method generates the polymer brush using a surface-immobilized activator coating followed by in situ polymerization.
Self-assembly techniques encompass the spontaneous assembly of polymer chain structures on the surface employing non-covalent bonds such as electrostatic interactions, and van der Waals forces. This technique is straightforward and adaptable, and it can be used to produce a wide variety of polymeric brushes.
Application in Nano-Based Antimicrobial Coatings
Bio-contamination of surgical instruments and prosthetics is a developing problem that contributes to health hazards and higher expenditures. In the fight against bio-contamination, developing fabricated substrates that reduce microbial adhesion while offering biocidal capability or combinatory benefits has emerged as a significant international approach.
A recent article published in Prosthetics discusses the importance as well as the applications of polymer brushes for nanotechnology-based coatings. Anti-fouling properties for implants are preferred to be provided by coatings based on chitosan. The synthesis of implantable sensor devices from chitosan specifically functionalized with polymer brushes derived from methacrylate has been a great success.
Functionalization of the surface reduced protein contamination, hindered leukocyte binding and prevented platelet activation. This method could be used to modify device implants or monitors with anti-fouling characteristics that enhance blood compatibility and cellular implantation.
Applications of Polymer Brushes in Silica Nanostructures
Regulating the chemical reactions between biological substances and substrates is crucial in nanobiotechnology. In recent years, numerous nanostructured silicon-based devices, such as nanopores and nanochannels, have been introduced. The most commonly utilized method for the incorporation of bio-selectivity and anti-fouling attributes is using polymer brushes.
One research article aimed at a simple technique for passivation or targeted biofunctionalization of silica using polymer brushes without polymerization reactions or vapor-phase accumulation. The substrate gets subjected to three distinct chemicals in succession over one hour.
Initially, aminopropylsilatrane is utilized to form a single-molecule layer of amines. A cross-linking agent coating and clicking chemistry are then used to render the exterior reactive toward thiols. The third stage involves preparing extremely dense and thick poly(ethylene glycol) brushes by grafting-to technique.
The altered substrates are preferable to extant silica alteration options, demonstrating ultralow contamination after being subjected to impure serum. The novel material eliminated the adhesion of an adhesive fluorescent protein on the inner surface of silica Nano channels measuring 150 nm by 100 nm. Additionally, it was functional with adjustments of solid-state Nanopores in 20 nm thin silicon nitride films and diminished ion current noise.
Uses of Polymer Brushes in Nano Architectonics
Nano-architected hybrid substances have become increasingly essential for optimizing energy conversion and storage device characteristics. Nanoscale interfacial phenomena are indispensable to the efficacy and durability of energy devices. In this way, interest in interfacial nanoarchitectonics with polymer brushes has increased due to its potential to circumvent multiple limitations. Polymer brushes provide a wide range of tools for manipulating interfacial characteristics and achieving molecular regulation of the synergistic combination of materials.
The recent article in Chemical Society Reviews provides a thorough overview of the applications of polymer brushes in nanoarchitectonics. On conductive materials, the development of redox-active polymer brushes can enhance the electron transfer features of energy conversion devices. In addition, the construction of composites by incorporating halloysite nanotubes (HNTs) amended with poly(sodium styrene sulfate) brushes (SHNTs) into chitosan (CS) frameworks has been advocated as a plausible method for fabricating hybrid films with improved proton conduction characteristics.
A novel concept for the fabrication of solid electrolytes with highly ion-conductive network channels for use in lithium ion batteries has also been proposed. This strategy relied on the three-dimensional formation of silica particles tweaked with polymer brushes composed of ionic liquids. Using graphene sheets with polymer brushes to create composite polymer electrolytes for lithium batteries is an additional intriguing strategy.
Other Significant Applications
Utilizing polymer bristles that function as well-defined and exceedingly uniform thin films have been used in sensors to enhance functionality and effectiveness. The polymer brush can either serve as the sensor's detection component or enhance its performance.
For the stabilization of colloidal particles, polymer brushes can be employed. This has been expanded to regulate and stabilize the development of colloidal crystals. Colloidal crystals are periodic structures formed by the self-assembly of sub-micrometer colloidal particles.
Polymer brushes have been utilized in nanolithography as resist elements for the etching of nanoscale patterning. The capability to accurately regulate the length and breadth of monomer chains renders them optimal for high-resolution pattern fabrication.
As a result of their exceptional physiochemical attributes, polymer brushes are an intriguing category of nanomaterials. The potential applications of polymer brushes in nanotechnology appear promising, and we can anticipate significant advancements in this field in the coming years.
References and Further Reading
Andersson, J. et. al. (2023). Polymer Brushes on Silica Nanostructures Prepared by Aminopropylsilatrane Click Chemistry: Superior Anti-fouling and Biofunctionality. ACS Applied Materials & Interfaces, 15(7). pp. 10228-10239. https://pubs.acs.org/doi/10.1021/acsami.2c21168
Erkoc P, Ulucan-Karnak F. (2021). Nanotechnology-Based Antimicrobial and Antiviral Surface Coating Strategies. Prosthesis. 3(1). pp. 25-52. https://www.mdpi.com/2673-1592/3/1/5
Giussi, J. M. et. al. (2019). Practical use of polymer brushes in sustainable energy applications: interfacial nanoarchitectonics for high-efficiency devices. Chemical Society Reviews, 48(3), pp. 814-849. https://pubs.rsc.org/en/content/articlelanding/2019/CS/C8CS00705E
Ritsema van Eck, G. et. al. (2022). Fundamentals and applications of polymer brushes in air. ACS Applied Polymer Materials, 4(5), pp. 3062-3087. https://pubs.acs.org/doi/10.1021/acsapm.1c01615