Poly brushes density

Surface force profiles between these polyelectrolyte brush layers have consisted of a long-range electrostatic repulsion and a short-range steric repulsion, as described earlier. Short-range steric repulsion has been analyzed quantitatively to provide the compressibility modulus per unit area (T) of the poly electrolyte brushes as a function of chain density (F) (Fig. 12a). The modulus F decreases linearly with a decrease in the chain density F, and suddenly increases beyond the critical density. The maximum value lies at F = 0.13 chain/nm. When we have decreased the chain density further, the modulus again linearly decreased relative to the chain density, which is natural for chains in the same state. The linear dependence of Y on F in both the low- and the high-density regions indicates that the jump in the compressibility modulus should be correlated with a kind of transition between the two different states. 

The density-dependent jump in the properties of poly electrolyte brushes has also been fonnd in the transfer ratio and the snrface potential of the brnshes [38], establishing the existence of the density (interchain distancej-dependent transition of polyelectrolytes in solntions. 

Yamamoto, S Tsujii, Y. and Fukuda, T. (2002) Glass transition temperatures of high-density poly(methyl methacrylate) brushes. Macromolecules, 35, 6077-6079. 

Non-spherical micelles of poly(ethylene)(PE)-poly(ethylene-propylene)(PEP) in decane are self-assembhng in the form of extended platelets that have a crystalline PE-core and a planar PEP brush on both sides. Due to the large size of the platelets the centre of mass diffusion is extremely slow and allows a clear separation of the density fluctuation in the brush. NSE experiments [301] have been analysed in terms of the model of de Gennes [300]. The friction coefficient and modulus of the brush were found to be similar to those of a typical gel. 

Poly(methyl methacrylate) with a variable degree of polymerization anchored to silica surfaces was synthesized following the room temperature ATRP polymerization scheme described earlier [45,46]. In the main part of Fig. 25 we plot the variation of the PMMA brush thickness after drying (measured by SE) as a function of the position on the substrate. Thickness increases continuously from one end of the substrate to the other. Since the density of polymerization initiators is (estimated to be 0.5 chains/nm ) uniform on the substrate, we ascribe the observed change in thickness to different lengths of polymer chains grown at various positions. 

Fig. 38 (Upper panel) Scanning force microscopy images of gold nanoparticles (diameter 17 nm) adsorbed along a surface-anchored poly(acryl amide) brush with a molecular weight gradient (Edge of each image = 1 p.m). (Lower panel) Dry thickness of poly(acryl amide) on the substrate before particle attachment (right, ) and particle number density profile (left, ). (Reproduced with permission from [140])...

Fig.44 (left) Dry thickness (in nm) of a poly(2-hydroxyethyl methacrylate) (PHEMA) brush in an orthogonal gradient as a function of the PHEMA grafting density and molecular weight The scale represents the thickness of dry polymer (in nm). (right) Adsorbed amount of lysozyme as a fimction of the position on the orthogonal PHEMA gradient. The scale represents the fluorescence intensity (in a.u.). (Reproduced with permission from [164])... 

Zhao B (2004) A combinatorial approach to study solvent-induced self-assembly of mixed poly (methyl methacrylate)/polystyrene brushes on planar silica substrates effect of relative grafting density. Langmuir 20 11748-11755... 

Surface-initiated ATRP was applied not only on planer substrates but also on various kinds of flne particles. The latter systems will be reviewed separately in Sect. 5.1. Porous materials are also fascinating targets for chromatographic application making use of the unique structure and properties of high-density polymer brushes. Wirth et al. were the first to report the grafting of poly(acrylamide) (PAAm) on a porous silica gel [109,110]. 

An alternative photo-SIP approach was described by Kang and coworkers, where they used an argon plasma to oxidize alkylthiolate SAMs on planar gold [55]. The plasma treatment oxidized carboxy-terminated SAMs to peroxide moieties. UV irradiation in the presence of acryhc acid and allylpentafluorobenzene yielded ultra-thin graft layers of 6-7nm. The poly(acrylic acid) layers were found to adsorb Fe " ions from solution. This particular photoinitiation method yields low-density polymer brush films. 

In a first example, for a densely grafted PEL brush system positively charged quaternized poly-4-vinylpyridine brushes have been prepared by following a two step approach [2, 63, 64, 66]. In the first step a neutral poly-4-vinylpyridine monolayer is prepared and, subsequently, charges are introduced by a second, polymer-analogous quaternization step. The grafting density of the parental neutral brush is adjusted by varying the polymerization time (Fig. 12) [63, 64]. The substrates were planar silicon substrates in... 

The extension of brush molecules is caused by excluded volume repulsion of the 2D-adsorbed side chains. Therefore, the length of adsorbed brushes should also depend on the grafting density. Copolymer brushes with a random sequence of methyl methacrylate and poly(n-butyl acrylate)-substituted methacrylate units were prepared with different compositions, i.e., grafting densities. Table 3 com-... 

Wu, T. Gong, P. Szleifer, I. Vlcek, P. Subr V. Grenzer, J., Behavior of surface-anchored poly(acrylic acid) brushes with grafting density gradients on solid substrates 1. experiment, Macromolecules 2007, 40, 8756-8764... 

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