Semidilute polymer brush

Wittmer, J., Johner, A., Joarmy J. F. and Binder, K. (1994) Chain desorption from a semidilute polymer brush - a Monte-Carlo simulation./. Chem. Phys., 101, 4379-4390. 

Figure 7 (a) Illustration of concentrated polymer brush (CPB) and semidilute polymer brush (SDPB) with the respective chain conformation in each regime, (b) Theoretically calculated threshold degree of polymerization for /VsDPB= /Ve as a function of particle core size Ro at various grafting density a. The curves are expected to approximately delineate the transition from fragile particle-like to polymer-like fracture. The dotted and dashed line denotes the particle size relevant to the presented experimental results with a grafting density (cr=0.5nm" ). 

The first theories that implemented a proper balance of intramolecular interactions and conformational elasticity of the branches were developed by Daoud and Cotton [21] and by Zhulina and Birshtein [22-24]. These theories use scaling concepts (the blob model), originally developed by de Gennes and Alexander to describe the structure of semidilute polymer solutions [64] and planar polymer brushes [65, 66]. Here, the monomer-monomer interactions were incorporated on the level of binary or ternary contacts (corresponding to good and theta-solvent conditions, respectively), and both dilute and semidilute solutions of star polymers were considered. Depending on the solvent quality and the intrinsic stiffness of the arms, the branches of a star could be locally swollen, or exhibit Gaussian statistics [22-24]. 

Amount of adhered L929 cells on semidilute (SD) and concentrated (CB) polymer brushes of PHEMA, PHEA, and PPEGMA as well as TCPS substrate. Incubation time = 24 h. [L929]q = 5.0 x 10 cells/cm. The vertical axis was normalized with the number of adherent cells on TCPS. 

Concentrated polymer brushes obtainable by SI-LRP prevented proteins and cells compared with the corresponding semidilute brushes, owing to the unique size-exclusion effect (of entropic origin) of the concentrated polymer brushes. This means that the physical structure (possibly including chain dynamics) of graft chains on the surface plays an essential role in bioinertness. 

So far, we have considered homogeneous segment density distributions in the brush structures. However, as in semidilute polymer solutions in good solvents, the screening of the excluded volume interaction is expected to produce blob structures. They are also at the basis of the theoretical imderstanding of polymer brushes due to Alexander and de Gennes [52,53[. 

ITP, TERP, and RTCP have successfully been applied to surface-initiated polymerizations of several monomers for preparing well-defined, dilute, semidilute, and concentrated polymer brushes on flat substrates and particles. These LRP techniques are attractive for their robustness, high monomer versatihty, and inducibility by photo-irradiation, for example, and widen the scope of surface-initiated polymerization. Access to a range of macromolecular surface designs could be beneficial for a variety of applications. 

The dynamical behavior of macromolecules in solution is strongly affected or even dominated by hydrodynamic interactions [6,104,105]. Erom a theoretical point of view, scaling relations predicted by the Zimm model for, e.g., the dependencies of dynamical quantities on the length of the polymer are, in general, accepted and confirmed [106]. Recent advances in experimental single-molecule techniques provide insight into the dynamics of individual polymers, and raise the need for a quantitative theoretical description in order to determine molecular parameters such as diffusion coefficients and relaxation times. Mesoscale hydrodynamic simulations can be used to verify the validity of theoretical models. Even more, such simulations are especially valuable when analytical methods fail, as for more complicated molecules such as polymer brushes, stars, ultrasoft colloids, or semidilute solutions, where hydrodynamic interactions are screened to a certain degree. Here, mesoscale simulations still provide a full characterization of the polymer dynamics. 

In certain cases a higher degree of irreversibility is observed. This is the case for the so-called pseudo-brushes where the monomer adsorption on the surface is supposed to be irreversible and where the loop size distribution remains fixed under swelling. A pseudobrush is obtained by placing the adsorbing surface in contact with a molten polymer (or a concentrated semidilute solution). All the chains within one Gaussian radius of gyration R N I a adsorb on the surface and the adsorbance is The adsorption is... 

Marra A, Peuvrel-Disdier E, Wittemann A, Guo X, Ballauff M Rheology of dilute and semidilute suspensions of spherical polyelectrolyte brushes. Colloid Polym Sci 281 491 96, 2003. 

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