Trains, and Tails

Of particular interest has been the study of the polymer configurations at the solid-liquid interface. Beginning with lattice theories, early models of polymer adsorption captured most of the features of adsorption such as the loop, train, and tail structures and the influence of the surface interaction parameter (see Refs. 57, 58, 62 for reviews of older theories). These lattice models have been expanded on in recent years using modem computational methods [63,64] and have allowed the calculation of equilibrium partitioning between a poly-... 

FIGURE 5.25 Polymeric chains adsorbed at an interface (a) terminally anchored polymer chain of mean end-to-end distance L (b) a brush of anchored chains (c) adsorbed (but not anchored) polymer coils (d) configuration with a loop, trains, and tails (e) bridging of two surfaces by adsorbed polymer chains. 

FIGURE 14.2. When polymers adsorb at a surface, only a fraction of the monomer units need be involved for strong binding to occur. As a result, the configurations of the adsorbed chains can vary from the least likely end-group attachment (a) to the more random (and more probable) attachments as loops, trains, and tails (b). 

At the microscopic level, it is possible to visualize the adsorbed chain in the fraction of segments in loops, trains, and tails. Figure 11 shows the distribution of three fractions as generated by the MC method. For the adsorbed layers, the surface appears to be dominated by tails.(85) This may be important in terms of adhesion. By tailormaking the kind of tails, we can perhaps achieve a certain type of adhesion to a selected surface. 

FIGURE 11. Fraction of segments in loops (A), trains ( ), and tails ( ) as a function of the adsorbed amount. Xs = ( -5, Xs = chain length 101 segments, generated by the Monte Carlo method. [From T. Cosgrove, Chem. Ind. 45 (January, 1988), reproduced with permission..]... 

Figure 5.4. Schematic view of polymer adsorption at a solid-liquid interface showing loops, trains and tails and the corresponding segment distribution function, p(z).

Adsorbed polymeric molecules may form not only brushes (Fig. 28b) but also coils of macromolecules, like proteins, which can also adsorb at a liquid surface—Fig. 28c. Sometimes, the configurations of the adsorbed polymers are very different from the statistical coil Loops, trains, and tails can be distinguished (Fig. 28d). 

The early theoretical picture given by Simah and co-workers [33] showed that the equilibrium adsorbed polymer chain on a solid surface consists of three types of segment sequences trains (adsorbed segments), loops (sequences of free segments connecting successive trains), and tails (non-adsorbed chain ends). Later... 

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