Buoy segment

Numerous examples of these systems have been studied experimentally. Tirrell et ah measured the adsorption of AB copolymers of polystyrene and polyvinylpyridine on mica. A wide range of molecular weights was tested, and it was found that, for most samples, about 200 ng/cm of polymer adsorbed to the surface, and that the buoy segments easily formed polymer combs , unless the size of the anchoring segment was too large. The maximum surface density was found with small... 

The adsorption of block and graft copolymers is more complex, as the intimate structure of the chain will determine the extent of adsorption [37]. Random copolymers adsorb in an intermediate fashion compared to that of the corresponding homopolymers. Block copolymers retain the adsorption preference of the individual blocks. The hydrophilic block (e.g., PEO the buoy) extends away from the particle surface into the bulk solution, while the hydrophobic anchor block (e.g., PS or PPO) provides a firm attachment to the surface. Figure 6.14 shows the theoretical prediction of diblock copolymer adsorption according to SF theory. In this case, the surface density cr was plotted versus the fraction of anchor segments v, and adsorption was shown to depend on the anchor/buoy composition. 

Figure 6.18 shows the hydrodynamic thickness versus fraction of anchor segment for an ABA block copolymer of PEO-PPO-PEO [37]. The theoretical (SF) predictions of adsorbed amount and layer thickness versus fraction of anchor segment are shown in the inserts of Figure 6.18. In the presence of two buoy blocks and a central anchor block (as in the above example), the A-B-A block showed a similar...

Figures 7 and 8 show the theoretical adsorption and hydrodynamic layer thickness behavior of an AB block copolymer, but as can be seen from these figures, fhey depend on the anchor/buoy composition. In general, the adsorbed amounts are higher than is the case for homopolymers and the adsorbed layer more extended and more dense. Maximum levels of adsorption are achieved when around 10% of the segments are anchors. In principle, then, these materials are better steric stabilizers than homopolymers.

The segment density distribution of block copolymers gives a different pattern, since the hydrophilic block (the buoy) extends away from the surface into bulk solution, whereas the lyophobic anchor block provides firm attachment to the surface. This is illustrated in Fig. 6, which shows the theoretical adsorption and hydrodynamic layer thickness behavior of an AB block copolymer according to Schuetjens and Fleer s theory [17]. 

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