## Abstract

The renormalized one-loop theory is a coarse-grained theory of corrections to the random phase approximation (RPA) theory of composition fluctuations. We present predictions of corrections to the RPA for the structure function S (k) and to the random walk model of single-chain statics in binary homopolymer blends. We consider an apparent interaction parameter χ_{a} that is defined by applying the RPA to the small k limit of S (k). The predicted deviation of χ_{a} from its long chain limit is proportional to N^{-1/2}, where N is the chain length. This deviation is positive (i.e., destabilizing) for weakly nonideal mixtures, with χ_{a} N1, but negative (stabilizing) near the critical point. The positive correction to χ_{a} for low values of χ_{a} N is a result of the fact that monomers in mixtures of shorter chains are slightly less strongly shielded from intermolecular contacts. The predicted depression in χ_{a} near the critical point is a result of long-wavelength composition fluctuations. The one-loop theory predicts a shift in the critical temperature of O (N ^{-1/2}), which is much greater than the predicted O (N^{-1}) width of the Ginzburg region. Chain dimensions are found to deviate slightly from those of a random walk even in a one-component melt and contract slightly as thermodynamic repulsion is increased. Predictions for S (k) and single-chain properties are compared to published lattice Monte Carlo simulations.

Original language | English (US) |
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Article number | 224902 |

Journal | Journal of Chemical Physics |

Volume | 130 |

Issue number | 22 |

DOIs | |

State | Published - Jun 25 2009 |