Homopolymer solutions and blends

In this paper, we have reviewed some recent applications of the HPTMC method. We have attempted to demonstrate its versatility and usefulness with examples for Lennard-Jones fluids, asymmetric electrolytes, homopolymer solutions and blends, block copolymer and random copolymer solutions, semiflexible polymer solutions, and mixtures. For these systems, the proposed method can be orders of magnitude more efficient than traditional grand canonical or Gibbs ensemble simulation techniques. More importantly, the new method is remarkably simple and can be incorporated into existing simulation codes with minor modifications. We expect it to find widespread use in the simulation of complex, many-molecule systems. 

PT has also been used successfully to perform ergodic simulations with Lennard-Jones clusters in the canonical and microcanonical ensembles [53,54]. Using simulated tempering as well as PT, Irback and Sandelin studied the phase behavior of single homopolymers in a simple hydro-phobic/hydrophilic off-lattice model [55]. Yan and de Pablo [56] used multidimensional PT in the context of an expanded grand canonical ensemble to simulate polymer solutions and blends on a cubic lattice. They indicated that the new algorithm, which results from the combination of a biased, open ensemble and PT, performs more efficiently than previously available teehniques. In the context of atomistic simulations PT has been employed in a recent study by Bedrov and Smith [57] who report parallel... 

Blends of various compositions of PDMS (Mw, 650,000 M , 253,000) and PS (Mw, 100,000) were prepared by dissolution of the homopolymers in tetrahydrofuran, mixing the solutions and then rapidly removing the solvent using a freeze-drier. Blends were dried in a vacuum oven at 55 °C, sealed in... 

On the basis of these conclusions, some solutions may be proposed to correct the wrong effect of the morphology of the diblock copolymer. We therefore added a pure polyisoprene homopolymer to the blends which departed from the power law of Eq. (20). It can be observed in Fig. 16.5 that the level of the secondary elastic plateau modulus of these new blends [S1 -S1-1] [33, 34] can be corrected, and the power law [Eq. (20)] then obeyed, even at high diblock contents. 

Figure 6.12. G (T) for the homopolymers PS and PEO, the AB block copolymer 61, and a solution blend of the homopolymers having the composition of copolymer 61. Numbers in parentheses indicate the M in the order (PEO/PS). The B indicates method of preparation the C represents preparation by vacuum evaporation from chloroform solution. (Erhardt et aL, 1970.)...

In a dilute solution in a common good solvent for both blocks, the interactions between. different copolymers may be studied using the same direct renormalization procedures as the interactions between two homopolymers A and B equivalent to the two blocks.As for blends, in the asymptotic limit of infinite molecular masses, the chemical difference between the two blocks is irrelevant and the dimensionless virial coefficient gc between block copolymers defined by Eq. (10) is equal to the same value g as for homopolymers. The interactions which may provoke the formation of mesophases are here again due to the corrections to the scaling behavior ... 

In a dilute solution, blends of homopolymers A and B equivalent to the two blocks of the copolymers are compatible in a common good solvent contrary to what happens in a highly selective solvent, we do not expect mesophases to form in a dilute solution but only in semidilute and concentrated solutions. Mesophases formed by block copolymers in nonselective solvents have been studied many experimental groups, perhaps most recently bv Hashimoto et al. and Williams et al. The usual interpretation of experiments is based on the "dilution approximation" in which the phase diagram of a solution can be obtained from the corresponding pure copolymer phase diagram by replacing Xab AB where is the monomer volume fraction. We have seen in section... 

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