Segment density profile adsorbed polymers

Several experimental parameters have been used to describe the conformation of a polymer adsorbed at the solid-solution interface these include the thickness of the adsorbed layer (photon correlation spectroscopy(J ) (p.c.s.), small angle neutron scattering (2) (s.a.n.s.), ellipsometry (3) and force-distance measurements between adsorbed layers (A), and the surface bound fraction (e.s.r. (5), n.m.r. ( 6), calorimetry (7) and i.r. (8)). However, it is very difficult to describe the adsorbed layer with a single parameter and ideally the segment density profile of the adsorbed chain is required. Recently s.a.n.s. (9) has been used to obtain segment density profiles for polyethylene oxide (PEO) and partially hydrolysed polyvinyl alcohol adsorbed on polystyrene latex. For PEO, two types of system were examined one where the chains were terminally-anchored and the other where the polymer was physically adsorbed from solution. The profiles for these two... 

COSGROVE ET Al.. Adsorbed Polymer Segment Density Profiles... 

Segment density profiles and hydrodynamic thickness measurements have been made for polyethylene oxides adsorbed on polystyrene latex. Comparison with theoretical models shows that the hydro-dynamic thickness is determined by polymer segments (tails) at the extremity of the distribution. It is also concluded that the sensitivity of the s.a.n.s. experiment precludes the measurement of segments in this region and that the experimental segment density profiles are essentially dominated by loops and trains. 

Fig. 4.8 Segment density profiles at a flat wall for non-adsorbing polymers described as ideal chains (filled squares) mean-field chains (open circles) and excluded volume chains (open triangles) compared to the tanh profile (solid curve) of (4.18)...

The development of adsorption theory provides the explanation of the macromolecule behavior in the adsorption layer and provides the basis of arguments on the experimental results. A few theoretical models, describing the adsorbed macromolecule, are widely used now. Self-consistent field theory or mean field approach is used to calculate the respective distribution of trains, loops, and tails of flexible macromolecule in the adsorption layer [22-26]. It allows one to find the segment density distribution in the adsorption layer and to calculate the adsorption isotherms and average thickness of the adsorption layer. Scaling theory [27-29] is used to explain the influence of the macromolecule concentration in the adsorption layer on the segment density profile and its thickness. Renormalization group theory [30-33] is used to describe the excluded volume effects in polymer chains terminally attached to the surface. The Monte Carlo method has been used for the calculation of the density profile in the adsorption layer [33-35]. 

Theoretical and experimental investigations showed that, in the general case, the segment density profile of an adsorbed polymer can be divided on two sections the depletion region near the surface with practically constant concentration of monomer links of polymer and the region in which the segment density slowly decreased (Fig. 13). The relationship between link density and the distance from the surface in the second region can be described by... 

Figure 3 Density profile of a grafted polymer layer composed of chains with 100 segments and surface coverage al = 0.02. The full line corresponds to the polymers in the absence of model lysozyme. The broken line corresponds to the same polymer layer but after proteins are adsorbed on the surface to their equilibrium coverage. The dotted line corresponds to the density profile of the equilibrium amount of model protein adsorbed. The results were obtained using the generalized SCMF theory ...

In order to discuss a number of important quantities we consider the interfacial profile for the case of positive adsorption. Such a profile is sketched in fig. 5.6. It represents the polymer concentration dz) as a function of the distance z from the interface. The quantity c(z) is related to the volume fraction concentration profile of segments belonging to free molecules, having no contact with the surface. The excess adsorbed amount r (the amount of... 

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