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Tuesday, June 15, 2021

Scientists grew micellar polymer brushes on silicon and graphene

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Amit Kumar
Amit Kumar is editor-in-chief and founder of Revyuh Media. He has been ensuring journalistic quality and shaping the future of Revyuh.com - in terms of content, text, personnel and strategy. He also develops herself further, likes to learn new things and, as a trained mediator, considers communication and freedom to be essential in editorial cooperation. After studying and training at the Indian Institute of Journalism & Mass Communication He accompanied an ambitious Internet portal into the Afterlife and was editor of the Scroll Lib Foundation. After that He did public relations for the MNC's in India. Email: amit.kumar (at) revyuh (dot) com ICE : 00 91 (0) 99580 61723

A team of scientists grew polymer brushes on a silicon wafer and graphene oxide sheet, placing crystals on the surface that caused the growth of filaments. As a result, it was possible to control the density, length and chemical properties of micellar brushes, and using nanoparticles, scientists have shown the applicability of nanostructures for catalysis and the creation of antibacterial coatings.

In many areas (for example, lithography, the study of superhydrophobicity and cell adhesion), it is necessary to create nanostructures with precisely specified chemical and physical properties on the surface of materials. Hard surfaces can be modified by growing elongated polymer crystals on them, which are attached to them and together form polymer brushes. Synthesizing similar structures with precise characteristics on a larger scale, however, can be quite difficult.

Jiandong Cai and colleagues from ShanghaiTech University synthesized a nanostructure from copolymer filaments on a solid silicon surface. Polymer filaments were grown on a silicon wafer with silanol groups, which formed hydrogen bonds with molecules of cylindrical crystallites capable of growing “hairs” from block copolymers in solution on both sides.

Using an atomic force microscope, the authors of the work were convinced that the crystallites were distributed uniformly over the surface. Then the silicon wafer was placed in a solution of polydimethylsiloxane, which began to crystallize, forming a layer of nanoscopic brushes. From the images of the atomic force microscope, the authors determined that the length of the polymer columns is about a millimetre, and in diameter, they were about 20 nanometers. Control experiments confirmed that the brushes were formed due to the presence of crystallites on the silicon wafer: without them, the polymer formed cylindrical micelles in solution and hardly attached to the wafer.

By adjusting the density of the brushes depending on the concentration of crystallites on the plate, the authors were able to synthesize surfaces with different hydrophobicity – with a contact angle of 81 to 109 degrees. By adding trifluoroacetic acid, the researchers achieved protonation and the formation of a positive charge on the brush, because of which it became hydrophilic (a wetting angle of 26 degrees). The new material was also able to be modified with gold or silver nanoparticles, due to which it began to possess catalytic and antibacterial properties, respectively.

Modification of polymer brushes using strong acid, gold and silver nanoparticles
Modification of polymer brushes using strong acid, gold and silver nanoparticles

The height of the filaments was proportionally changed depending on the concentration of the polymer in the solution
The height of the filaments was proportionally changed depending on the concentration of the polymer in the solution

Scientists also managed to grow brushes on the surface of the graphene oxide sheet: they remained stable for several months, and the crystallites formed hydrogen bonds with carboxyl and hydroxyl groups on the sheet.

Thus, the authors were able to demonstrate the applicability of the obtained structure as an antibacterial membrane and catalyst. According to scientists, the presented method of surface modification also allows you to finely control some of its chemical and physical properties, which can be useful in many areas.

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