PMMA brushes

Figure 4.7 Fluorescence anisotropy decay curves for the PMMA brush swollen in benzene (filled circles) and the free PMMA chain in benzene solution at concentrations of 0.33 (triangles) and 2.9 X 10 g (open circles). The graft density of the brush is 0.46 chains nm . The solid curve indicates the instrument response function. Reproduced with permission from the American Chemical Society.

Figure 4.8 shows the fluorescence anisotropy decay curves for PMMA brushes with various graft densities swollen in benzene and acetonitrile. Benzene and acetonitrile are good and 0 solvents for PMMA. As clearly shown in this figure. 

Figure 4.9 Correlation time of the fluorescence anisotropy decay for the PMMA brush. The open and closed circles indicate the correlation times for the brush in acetonitrile and benzene, respectively.

The chain dimension in the height direction was evaluated as the thickness of the brush layer, I, relative to the chain contour length, io, by atomic force microscopy (AFM). Figure 4.10 shows the solvent dependence of the conformation of the PMMA brush. Whereas the brush chain changes its conformation in response to the solvent quality at the low graft density, the high-density PMMA brush does not show... 

Figure 4.10 Chain dimension of the PMMA brush in the normal direction to the substrate. L and Lq are the thickness ofthe brush layerand the contour length ofthe brush chain. The open and filled circles indicate the chain dimension in acetonitrile and benzene.

Figure4.11 Schematicdrawingofthe PMMA brush chain swollen in solvents, (a) brush with low graft density, (b) brush with high graft density. The left- and right-hand sides ofeach image illustrate the brush chains in poor and good solvents, respectively.

Figure 4.12 Fluorescence image of PMMA brush layer (a) and schematic drawing of the brush chain (b). The dark region (a) corresponds to the substrate surface exposed by scratching off the brush layer. The filled and open circles indicate the points where the fluorescence anisotropy decay was acquired.

Fig. 23 a, b. a An amplitude micrograph of PMMA brushes adsorbed on mica from a dilute solution in chloroform measured by tapping mode SFM. b Three-dimensional SFM micrograph of single brush-molecules indicated by the arrow in (a). The axial modulations have been explained by phase segregation of the side chains into nodules (insert) [82]... 

Fig. 9.31 a) Synthesis of PS-b-polyacrylate brushes by LCSIP and consecutive ATRSIP [282]. AFM images of the tethered PS-fa-PMMA brushes with 23 nm thick PS layer and 14 nm thick PMMA layer b) after treatment with CH2CI2, c) with cyclohexane and d) after solvent exchange from CHjClj to cyclohexane, e) Cartoon proposing a model for the regular nanopattern morphology ( pinned micelles )... 

Surface reconstruction of the PS-PMMA brush in selective solvents gave rise to pattern formation which was investigated by SPM, wetting experiments and XPS. The obtained morphologies depended on the thickness of the brush and its composition [283, 284] (Fig. 9.31). 

Fig. 9.36 a) Procedure of the preparation steps starting with the pCP of an inert SAM, self-assembly of a monolayer of initiator sites, ATRSIP and selective wet etching, b) (A) AFM image of a patterned brush of PMMA formed by this procedure. The bright areas correspond to PMMA brushes, while the dark regions correspond to the patterned areas of SAMs formed from HDT. (B) Cross-sectional profile of the patterned PMMA brush shown in (A). The location of the cross-sectional pro-... 

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. 2 AFM image of the tethered Si/Si02//PS-fc-PMMA brushes with 23 nm thick PS layer and 14 nm thick PMMA layer after a gradual treatment with cyclohexane...

Fig.9 Typical F/R vs. D curve between the PMMA brush (L = 87nm, Mn = 121700, Mw/Mn = 1.39) and the sUica probe (attached on an AFM cantilever). The arrowheads indicate critical distances is the equilibrium thickness at which a repulsive force is detectable, and Do is the offset distance beyond which the brush was no more compressible...

Fig. 10 Plots of Le/f-cw vs. dimensionless graft density a (1) PS brushes prepared by adsorption of PS-polydimethylsiloxane block copolymers (Mw,ps = 60000) and 0 (Mw,ps = 169000) [21,22]. (2) PEO brushes prepared by adsorption of PEO-PS block copolymers A (Mw.peo = 30800) and V (Mw.peo = 19600) [201]. (3) PMMA brushes prepared by surface-initiated ATRP (M = 31 300 267400). Data reprocessed from [116,117]...

Fig. 12 Retracting-mode force profiles of high-density PMMA brushes with and without P4VP terminal segment measured in toluene using a hydrophilic silica probe sphere...

The breakdown of the semi-dilute brush theory was also revealed in the force-distance curve of the high-density PMMA brush. Using the scaling approach [138], de Gennes derived the equation concerning the interaction force between two parallel plates with a semi-dilute polymer brush layer, predicting that the force-distance profiles should be scaled by plotting (F/i )... 

Fig. 14 Size-exclusion chromatograms of standard PSs for monolith columns with and without the high-density PMMA brush (Mn = 15000, M /Mn = 1.2, a = 0.6 chains nm ) on an inner surface. The inset shows a cartoon illustrating the size exclusion mode by the brush...

Tanaka et al. have studied the surface molecular motions of PS films coated on a solid substrate by lateral force microscopy and revealed that the Tg at the surface was much lower than the corresponding bulk one [148]. Possible reasons for this included an excess free volume induced by localized chain ends, a reduced cooperativity for of-relaxation process, a reduced entanglement, and a unique chain conformation at the surface. For comparison, they examined surface relaxation behavior of high-density PMMA brushes. 

Fig. 17 Typical lateral force-temperature curves for the PMMA brush (Mn = 45400, Mw/Mn <1.2, a = 0.8 chains nm ) and an equivalent spin-coated film at the scanning rate of 10" nms . Reproduced with permission from [148] (Copyright 2003 The Society of Polymer Science, Japan)...

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