Swollen 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.

Benmouna, F. Peng, B. Gapinski, J. Patkowski. A. Ruhe. J. Johannsmann, D. Dynamic light scattering from liquid crystal polymer brushes swollen in a nematic solvent. Liq. Cry St. 2001, 2S, 1353- 1360. 

Figure 17 Schematic depiction of a LC brush swollen in a low molecular weight nematic. Competing orienting actions from the brush and the bare surface may result in a tilted alignment. The chemical structure of the sidechain mesogen used in this study is indicated in the inset.

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. 

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.

A 17-year-old woman with cystic fibrosis is evaluated for knee pain. On review of systems, she also notes persistent bleeding from cuts in her skin and bleeding of her gums after brushing her teeth. Physical examination is remarkable for an obviously swollen right knee that is tender with limited range of motion. Fluid drained from the knee is bloody (hemarthrosis). Her complete blood count is normal, but prothrombin time is elevated. 

The present model is based on several assumptions (i) the possible configurations of the grafted chain are described by a random walk (ii) their free energy densities are expressed as functions of the local monomer volume fraction alone (iii) the configurations of minimum energy dominate the partition function of the system (iv) only the configurations with monomers distributed between the surface and the position of the last monomer of the chain, assumed to be the farthest one, are taken into account. The latter assumption basically implies that the probability that the most distant monomer from the surface reaches the distance z is equal to the probability that the last monomer of the chain reaches this distance this approximation clearly fails when z is in the vicinity of the surface. However, in swollen brushes the behavior of the monomers in the vicinity of the surface is less important than the behavior of the distant monomers, which are primarily responsible for the brush thickness and for the interactions between brushes. 

Butadiene styrene Toluene 1. Abrasion followed by brushing. Grit or vapor blast or 280-grit emery cloth followed by solvent wipe. 2. Prime with butadiene styrene adhesive in an aliphatic solvent. 3. Etch surface for 1-5 min at RT following method 2 for natural rubber. Excess toluene results in swollen rubber. A 20-min drying time will restore the part to its original dimensions... 

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