Homopolymer brushes

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

The brash layer thickness (dry collapsed state) obtained after seven days of polymerization time and successive soxhlet extraction was found to be approx. 10 nm and very uniform ( 0.3 nm). The uniform thickness values are provided by the homogeneous initiation, polymerization and termination reaction. Meanwhile poly(2-oxazoline) homopolymers brushes with layer thicknesses of 20 to 30 nm can be obtained [275]. 

Another strategy to control surface morphologies and properties by using self-assembling properties of polymer chains is to randomly graft different kinds of homopolymers on a surface. In recent years, such a mixed homopolymer brush has been extensively investigated both theoretically and... 

Fig. 21 Topographic AFM images of PMMA/PS-mixed homopolymer brushes with different ratios of (Tpmma and aps but nearly equal opmma + <7ps 0-5 chains nm ) after treatment with acetone, where

In this type of mixed brush one may expect also quite large diversity of combinations. Here we present one example of the mixed brush fabricated from oppositely charged weak PEs—the PAA-P2VP mixed brush. The IEP point of the brush (pH 5.6) is in between those of the corresponding homopolymer brushes (PAA pH 3.2 P2VP pH 6.7) indicating the area when the brush is neutral and opposite charges compensate each other in the brush. 

Figure 10.6 Procedure for polymer nanowire fabrication. An aqueous PEDOTtPSS solution was spin-coated on a substrate patterned with a 1.3 ym period grating, then coated with a thin Si02 layer and a PDMS homopolymer brush. A PS-PDMS block-copolymer thin film was then spin-coated and solvent-annealed. The self-assembled block-copolymer patterns were transferred into the underlying PEDOT-.PSS film through a series of reactive ion etching steps employing CF4 and O2 plasmas. (Reprinted with permission from Nano Letters, Nanowire Conductive Polymer Gas Sensor Patterned Using Self-Assembled Block Copolymer Lithography by Y. S. Jung et al., 8, 11. Copyright (2008) American Chemical Society)...

Figure 10.1 Various structures of CPBs. (a) Homopolymer brush (b) Core-shell brush (c) Core-shell-corona brush ...

B. Zhao,Synthesis of binary mixed homopolymer brushes by combining atom transfer polymerization and nitroxide-mediated radical polymerization. Polymer 2003, 44, 4079-4083. 

Li, D., X. Sheng, and B. Zhao. 2005. Environmentally responsive Hairy nanoparticles Mixed homopolymer brushes on sUica nanoparticles synthesized by hving radical polymerization techniques. Journal of the American Chemical Society 127, no. 17 6248-6256. doi 10.1021/ja0422561. 

A nice example is given by Lei et al. (2013), in which they studied adsorption of lysozyme on poly(2-(dimethylamino ethyl) methacrylate)-block-poly(methaaylic acid) (PDMAEMA-b-PMAA) diblock-copolymer brushes (Figure 5.14). Lysozyme has a relatively high isoelectric point (/p=ll.l) thus controlling its adsorption (on Si) by pH is too difficult. It has been shown that lysozyme adsorption decreases on weak base polyelectrolyte, PDMAEMA, and increases on weak acid polyelectrolyte, PMAA brushes. Authors show that the thickness of the PMAA block in PDMAEMA-b-PMAA is critical when the outer PMAA block is less than 10 nm, adsorption of the lysozyme increases with pH. Lysozyme adsorption reached to 16.4-fold more at pH 10 compared with its value at pH 4. At thicker regimes (>10nm), diblock-copolymer brush exhibited similar behavior to that of PMAA homopolymer brush. 

Motomov, M., Sheparovych, R., Katz, E., and Minko, S. 2008. Chemical gating with nanostructured responsive jxrlymer brushes mixed brush versus homopolymer brush. ACS Nano 2 41-52. 

The simplest case is the preparation of homopolymer brushes. For example, PNIPAM brushes have been developed for cantilever actuation and the detection of changes in solvent type, temperature and pH, promising great potential for sensing applications in nucrofluidic devices (Abu-Lail et al., 2006 Qing and Sun, 2011). Tokareva et al (2004) prepared a novel sensor for pH detection based on poly(2-vinylpyridine) polymer brushes which detected a change in pH from 5 to 2. 

Block copolymer brushes obey the same power-law dependence of hydrodynamic transfer on molecular weight as do homopolymer brushes under solvent conditions. The poly(N-isopropylacrylamide)-containing block copolymer brushes were sensitive to changes in the environment, as shown by a decrease in hydrodynamic transfer with increasing temperature of the medium. 

Zhang P, Li B, Wang Q. Quantitative study of fluctuation effects by fast lattice Monte Carlo simulations. 2. Homopolymer brushes in an implicit, good solvent. Macromolecules 2011 44 7837. 

Homopolymer brush constituted of end-tethered chains stretched in good solvent (a), and collapsed in poor solvent (b). 

Although homopolymer brushes demonstrate very pronounced responsiveness in terms of switching their properties between good and poor interactions with their environment, the composition of the interface is not changed qualitatively. In other words, independent of the environment, the polymer exposed to the interface remains unchanged in its chemical nature. Thus, the switching of the thin film properties is limited by the constitution of the given polymer. 

Li DJ, Sheng X, Zhao B (2005) Environmentally responsive Hairy nanoparticles mixed homopolymer brushes on silica nanoparticles synthesized by living radical polymerization techniques. J Am Chem Soc 127 6248-6256... 

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