Copolymer coverage

Fig. 39. Schematic of the conformation of block copolymers inside lamellae a diblocks and b triblocks. The bridging effect of triblock copolymers is responsible for their better mechanical reinforcement at high copolymer coverage...

Fig. 47. Fracture toughness gc (A) at high copolymer coverage (saturation values), and fraction of deuterium on the PS side of the interface after fracture ( ) at low copolymer coverage, as a function of copolymer composition/, a Poly(styrene-d8-co-4-hydroxystyrene) b poly(styrene-d8-co-4-vinyl-AT-ethylbenzamide) and c poly(styrene-d8-co-4-vinylbenza-mide). Data from [77]...

Figure 6.4 Schematic description of the three regimes of the copolymer coverage at an interface as a fimction of time (a) S(t) ki ,opot, (b) S(t) = 1.13/Oo(DcoMt , (c) S(t) oc In t (after Fredrickson and Milner [16])...

In the late stage of the reaction corresponding to t > t< the copolymer coverage has reached the point, S, that saturation of the interface by the copolymer layer presents a significant chemical potential barrier to the reactive chains. T e reaction rate is then reduced drastically in an exponential manner, i.e.,... 

It should be noted that when the copolymer coverage has approached S, the concentrations of the reactive chains just outside the copolymer layer, Pa and Pb, are still very close to po- Thus reactive chain depletion effects are negligible in this regime but copolymer saturation effects are critical. In other words, these reactive chains will have much difficulty... 

As stated above, once the copolymer coverage has reached S, reactive chains located just outside the copolymer layer can hardly reach the interface to react with then-counterparts unless further mixing will bring them together. This implies that under the conditions of diffiision-controiied reaction with 1 and tp,ocess > tcopolymer formed at the interface is approximately proportional to the area of the interfaces available for the reaction. This conclusion can be used to evaluate the capacities of different types of mixers to generate interfaces. 

Finally, we briefly mention interactions due to adsorbing polymers. Block copolymers, witli one block strongly adsorbing to tire particles, have already been mentioned above. Flere, we focus on homopolymers tliat adsorb moderately strongly to tire particles. If tliis can be done such tliat a high surface coverage is achieved, tire adsorbed polymer layer may again produce a steric stabilization between tire particles. 

The book consists of four articles reviewing the literature based on the authors own experiences over the last decade in this field. It does not claim to be exhaustive nor to provide complete coverage of the very extensive literature in this field. Instead, it focuses on the currently intense areas of research namely living polymerization, block copolymer synthesis, synthesis of dendrimers and finally macroporous thermosets. Hopefully, this volume will not only serve as a book on the design of macromolecular architectures but also as a source of inspiration to produce polymers combining several functional properties. 

Parkinson, E.L., Ettelaie, R., Dickinson, E. (2005). Using self-consistent-field theory to understand enhanced steric stabilization by casein-like copolymers at low surface coverage in mixed protein layers. Biomacromolecules, 6, 3018-3029. 

Balazs and Lewandowski (1990) have performed simulations of the adsorption of triblock copolymers onto a planar surface, and examined the conformations of the adsorbed chains. Monte Carlo simulations were performed of the motion of hydrophilic-hydrophobic chains on a cubic lattice. These simulations revealed a complex structure in the interfacial region due to the self-assembly of chains, driven by the solvent-incompatible block, reducing adsorption onto the surface. The influence on the surface coverage of length of the hydrophilic segement, polymer concentration, interaction energy between hydrophilic block and the... 

However, the surface coverage is the same for both copolymers when weakly adsorbed to the surface. Surface density profiles were also compared. Finally, scaling relationships for triblock copolymer adsorption under weak adsorption conditions were derived (Haliloglu et al. 1997). In a related paper (Nguyen-Misra et al. 1996), adsorption and bridging of triblock copolymers in an athermal solvent and confined between two parallel flat surfaces were studied, and the dynamic response of the system to sinusoidal and step shear was examined. 

This model was used in dispersion polymerization to predict the size of polymer particles stabilized through grafting on hydrophilic polymers such as PVPo. It provides a reasonable description of, for example, PVPo-stabilized polymerization of styrene in polar solvents. The present model does not apply to other types of dispersion polymerization where grafted comb or block copolymer stabilizers are active. The key controlling parameters in this model are the availability of graft and the minimum and maximum coverage, Qmin and Qmax. 

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