Polymer Brush Coatings

FIGURE 20.6 Conformational states of polymer chains grafted at a snrface (a) mnshroom and (b) brnsh. 

FIGURE 20.7 Gibbs energy of adhesion of a particle at a brush-coated, charged substratum surface as a function of separation distance (—), made up of four types of contributions (1) short-range particle-substratum attraction (2) dispersive attraction (3) electrostatic repulsion due to overlap of Uke-charged electrical double layers and (4) osmotic repulsion due to compression of the polymer brush. 

FIGURE 20.8 Micrographs of (a) Staphylococcus epidermidis and (b) Candida albicans around the border zone between glass (left-hand side) and PEO brush-coated glass (right-hand side). Bars 10 om (a) and 40 pm (b). (Adapted from Roosjen, A. et al. Microbiology 149 3229, 2003.) 

Diminishing secondary adhesion can only be achieved in a thermodynamic way, that is, by sufficiently reducing the depth of the secondary minimum. This is realized by increasing the thickness L of the brush, which, in turn, is determined by the length of the polymer chains and the grafting density. 

FIGURE 20.9 Adsorption of proteins from human blood plasma on a PEO brush-coated polystyrene (PS) surface as a function of the (reciprocal) PEO grafting density. (Adapted from Norde, W. and Gage, R.A. Langmuir 20, 4162, 2004.) 

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A special case of steric stabilization may be achieved by coating the surface with a polymer brush. Such brushes are obtained by end-grafting highly soluble polymer molecules to a surface. Polymer brushes are applied to surfaces at which deposition of other particles, such as, globular proteins, microorganisms, or other biological cells, has to be prevented. We return to the use of polymer brush coatings in Section 20.4.3. 

The micrographs in Figure 20.8 show that microbial adhesion can be successfully suppressed by a polymer brush coating. 

New topics, including phase separations in polymer systems, electrokinetics of charged permeable surface coatings, and polymer brush coatings to control adsorption and adhesion of particles... 

Auftrageverfahren) polym brush coating Buttersaure/Butansaure (Butyrat)... 

B.B. Prasad, K. Tiwari, M. Singh, PS. Sharma, A.K. Patel and S. Srivastava, Ultratrace analysis of dopamine using a combination of imprinted polymer-brush-coated SPME and imprinted polymer sensor techniques, Chromatographia, 69 (9-10) 949-957, 2009. 

Muszanska, A.K., Rochford, E.T.J., Gruszka, A., Bastian, A.A., Busscher, H. J., Norde, W., et al., 2014. Antiadhesive polymer brush coating functionalized with antimicrobial and RGD peptides to reduce biofilm formation and enhance tissue integration. Biomacromolecules 15, 2019-2026. http //dx.doi.org/10.1021/bm500168s. 

A triblock copolymer, Pluronic F-68, (polyethylene oxide-polypropylene oxide- polyethylene oxide triblock copolymer), a synthetic surfactant [74] was adsorbed to hydrophobic substrata such as PDMS to form low-density polymer brush-coatings [86]. The PEO-PPO-PEO triblock copolymers in many ways exhibit a similar behavior as low molecular weight non-ionic surfactants. The tendency of these amphiphilic polymers to self-assemble in aqueous systems and at interfaces has led to widespread applications for the stabilization of macromolecular colloidal suspensions and for the manipulation of surface properties [92]. Anti-fouling properties of Pluronic copolymers result from the fact that the Pluronic copolymers PPO domain, which... 

FIG. 4 Sterically stabilized colloidal particles are coated with short polymer brushes. A hard sphere-like interaction arises. 

A new brush-type CSP, the Whelk-0 1, was used by Blum et al. for the analytical and preparative-scale separations of racemic pharmaceutical compounds, including verapamil and ketoprofen. A comparison of LC and SFC revealed the superiority of SFC in terms of efficiency and speed of method development [50]. The Whelk-0 1 selector and its homologues have also been incorporated into polysiloxanes. The resulting polymers were coated on silica and thermally immobilized. Higher efficiencies were observed when these CSPs were used with sub- and supercritical fluids as eluents, and a greater number of compounds were resolved in SFC compared to LC. Compounds such as flurbiprofen, warfarin, and benzoin were enantioresolved with a modified CO, eluent [37]. 

It is beyond the scope of this Chapter to discuss all kinds of various coating techniques, properties of the supports, properties of the coatings and the various fields of application of the composites in catalysis, separation techniques, materials science, colloid science, sensor technology, biocompatible materials, biomi-metic materials, optics etc. The scope had to be restricted to the fundamental properties of ultrathin organic layers on solid supports followed by some examples, outlining the benefit of the tailored functional surfaces such as SAM and polymer brushes for catalysis. 

In the second part of this Chapter the thickness of the organic layer under discussion is slightly increased and a closer look at recent developments of more complex surface-bonded systems involving polymers is outlined. Despite the introduction of flexible polymer chains, the surface coating should still be defined and uncontrolled heterogeneities minimized. Here, especially, polymer brush-type layers where self-assembled monolayers (SAMs) are used as two-dimensional template systems for the preparation of well-defined surface coatings will be subject of a more detailed discussion. 

The use of polymeric coatings in catalysis is mainly restricted to the physical and sometimes chemical immobilization of molecular catalysts into the bulk polymer [166, 167]. The catalytic efficiency is often impaired by the local reorganization of polymer attached catalytic sites or the swelling/shrinking of the entire polymer matrix. This results in problems of restricted mass transport and consequently low efficiency of the polymer-supported catalysts. An alternative could be a defined polymer coating on a solid substrate with equally accessible catalytic sites attached to the polymer (side chain) and uniform behavior of the polymer layer upon changes in the environment, such as polymer brushes. 

The interest in polymer brushes and defined polymer coatings prepared via SIP is not at all restricted to the polymer community or the surface science community. The demand for tailored, fimctionahzed and adaptive surfaces comes from a multitude of scientific branches and also from industry. Possible applications are already discussed in many of the contributions compiled here. Besides polymer science, surface chemistry and physics, they include catalysis, biomedical applications, microfluidics and nanotechnology. This creates a highly interdisciplinary, Hvely and fruitful environment. 

Fig. 5. Microbubbles coated with a shell of lipid/surfactant below the critical temperature, especially armored with an additional steric protection polymer brush layer, do not fuse. Longterm storage of pre-formed microbubbles in the aqueous phase is feasible...

Fine Particles Coated with High-Density Polymer Brushes... 

This section reviews studies on the synthesis of fine particles coated with polymer brushes by surface-initiated ATRP. SiP are among the most extensively studied particles for the application of surface-initiated ATRP [85-93]. Patten et al. first succeeded in the surface-initiated ATRP of ST and MMA on two SiPs with average diameters of 75 and 300 nm [85,86]. Several groups investigated the synthesis of hybrid SiP with different monomers. Maty-jaszewski et al. synthesized an initiator-functionalized SiP with a diameter of... 

Owing to the simphcity and versatility of surface-initiated ATRP, the above-mentioned AuNP work may be extended to other particles for their two- or three-dimensionally ordered assemblies with a wide controllabiUty of lattice parameters. In fact, a dispersion of monodisperse SiPs coated with high-density PMMA brushes showed an iridescent color, in organic solvents (e.g., toluene), suggesting the formation of a colloidal crystal [108]. To clarify this phenomenon, the direct observation of the concentrated dispersion of a rhodamine-labeled SiP coated with a high-density polymer brush was carried out by confocal laser scanning microscopy. As shown in Fig. 23, the experiment revealed that the hybrid particles formed a wide range of three-dimensional array with a periodic structure. This will open up a new route to the fabrication of colloidal crystals. 

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