A Bettachy | PubMed Health

PubMed2005

Kinetics of microphase separation in interpenetrated polymer networks in solution.

We present here a theoretical study of the early kinetics of the microphase separation in crosslinked polymer blends, made of two incompatible polymers A and B, dissolved in a common good solvent. Use is made of an extended blob model used previously for the investigation of the static properties of such a transition. We are interested in the variation of the relaxation rate, tau(q), versus the wave number q, in the vicinity of the spinodal temperature. We first show that kinetics is entirely dominated by local motions, which are of Rouse type. Slow motions are absent, because of the permanent presence of crosslinks. Second, we find that the characteristic frequency, omega (q) = tau(q)(-1), increases with increasing wave number q according to a sixth power law, that is omega (q) approximately q6 phi(-9/4), where phi is the overall monomer volume fraction. Therefore, the swelling of strands due to the excluded-volume forces leads to a renormalization of the characteristic frequency by a multiplicative factor scaling as phi(-9/4). The main conclusion is that the presence of a good solvent necessitates relaxation rates less important than those relative to crosslinked mixtures in the molten state.

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PubMed2004

Exact effective force between star-polymers in a Theta-solvent.

We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f(1) and f(2), immersed in a common Theta-solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones. We first show that, in dimension d = 3, the force, F(r), decreases with the center-to-center distance r as F(r)/kappa BT congruent with Af1f2 x [r ln (R2/r2]-1 (r<R), with the exact universal amplitude Af1f2 = f1f2(f1 + f2 - 2)/22. Second, in dimension d = 2, we find that the force decays more slowly as F(r)/kappa BT congruent with Bf1f2 x r-1 (r<R), with the exact universal amplitude Bf1f2. For high distances compared to the gyration radius, R approximately a square root of N, of a single polymer chain at the Theta-point, an exponential decay of the force is expected.

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