Polymer brushes have become a significant focus of polymer research with the need for straightforward and versatile surface modification. With the development of controlled radical polymerization from surfaces, new theoretical models, and sophisticated characterization tools, the resulting ability to control brush density and brush thickness gives unparalleled control over surface properties and functionality. By increasing brush density, a stretched brush conformation is formed as a result of constraining the cross-sectional area of that brush strand which thereby influences the interactions of molecules with the brush surface. The associated residual stress also gives polymer brushes properties distinct from an equivalent layer of coated polymer chains. Examples of uncharged and charged “grown from” polymer brushes, the effect of architecture on physical behavior, and the influence of nanoscale patterning will be described. The use of brush surfaces in biology relevant applications will be discussed and include resistance to nonspecific binding, cell bioadhesion, their use as platforms for biosensors, thermoresponsive surfaces, and targeted protein binding.
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Direct covalent functionalization of large‐area single‐layer hexagonal boron nitride (hBN) with various polymer brushes under mild conditions is presented. The photopolymerization of vinyl monomers results in the formation of thick and homogeneous (micropatterned, gradient) polymer brushes covalently bound to hBN. The brush layer mechanically and chemically stabilizes the material and allows facile handling as well as long‐term use in water splitting hydrogen evolution reactions.
Mixed polymer brushes of rod-type polypeptide and coiltype vinyl polymer brushes were synthesized via two sequential steps of vapor deposition surface-initiated ring-opening polymerization (SI-ROP) and surface-initiated atom transfer radical polymerization (SI-ATRP), respectively. The effect on polypeptide brushes by coil-type brushes of their surface morphology, film thickness, and orientation were investigated before and after solvent quenching processes using chloroform and acetone. Before solvent quenching, the as-grown coil-type brushes forced the polypeptide brushes to stand up from the surface, resulting in higher film thickness, but the polypeptide brushes remained randomly oriented. After solvent quenching, polypeptide brushes tended to aggregate into conical bundles with an orientation perpendicular to the substrate, but coil-type brushes restricted the free arrangement of the polypeptide brushes and lessen their upward movement. Changes in film thickness, rod orientation, morphology, and wettability were observed with increased molecular weight of the coil-type polymer in the mixed brushes.
In this study of nanopatterned helical poly(benzyl-l-glutamate) (PBLG) brushes, rod-type brush arrays were fabricated via an integrated process of high-resolution lithography and surface-initiated vapor deposition polymerization (SI-VDP). “Nanospikes” of polymer brushes with spacings of less than 100 nm were produced. The topology and areal behavior of the resulting patterned rod-like brushes were analyzed and compared with patterned coil-type brushes. A geometric study of these self-assembled “nanospikes” was carried out, and their cross sections were investigated via focused ion beam (FIB) and scanning electron microscopy (SEM). Furthermore, the presence of poly(N-isopropylacrylamide) (PNIPAM) brushes in unpatterned regions was shown to inhibit undesired “inter-spike” bridging of the PBLG brushes, resulting in more well-defined nanostructures. It was shown that rod-like polypeptide brushes are capable of self-segregation and become arranged vertically without any external support from their surroundings, to form a rod bundle end-point functional topography that could provide possible pathways for studies of model biological surfaces, directed assembly of nanoparticles, or binary mixed brush surfaces with dual properties.
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