We provide a new approach to describe the component segmental dynamics of miscible polymer blends combining the concept of chain connectivity, expressed in terms of the self-concentration, and the Adam-Gibbs model. The results show an excellent agreement between the prediction of our approach and the experimental data. The self-concentrations obtained yield length scales between 1 and 3.2 nm depending on the temperature, the flexibility of the polymer, expressed in terms of the Kuhn segment, and its concentration in the blends, at temperatures above the glass transition range of the blend.

The dynamic heterogeneity of the segmental dynamics in miscible polymer blends has been alternatively interpreted in terms of either chain connectivity effects or thermal concentration fluctuations. Taking into account that both phenomena seem to be relevant, in this work we propose a minimal model which combines these two effects. This model basically assumes the self-concentration approach recently proposed by Lodge and McLeish [Macromolecules 2000, 33, 5278] and introduces a distribution of the effective concentration around a given segment mainly due to the effect of thermal concentration fluctuations. The proposed model has been checked in two blend systems, PVME/PS and PoCLS/PS700. Each of these systems allows to selectively observe by dielectric spectroscopy either the low-or highglass transition temperature component of the blend, respectively. The model provides a good quantitative description of the dielectric segmental relaxation in both cases with only one free parameter: the variance of the distribution of the effective concentration. This parameter results to be hardly dependent on temperature, at least in the two blends investigated.

No abstract

To explore the ability of the "effective concentration" model to quantitatively predict the individual local dynamics of each component in miscible polymer blends, three model systems [polystyrene/ poly(vinyl methyl ether), polystyrene/poly(o-chlorostyrene), and poly(vinyl methyl ether)/poly(o-chlorostyrene)] are studied using differential scanning calorimetry and thermally stimulated depolarization current, this second technique allowing to measure the effective T g of the dielectrically active component in the blend. Final results show a very good agreement between measured effective glass transition temperatures and those predicted by the model.

The two components of the segmental dynamics of poly(vinylethylene) (PVE) and polyisoprene (PIP) miscible blends, as observed dielectrically, are resolved and analyzed. This analysis is based upon a generalization of the CONTIN algorithm for inverse Laplace transformations presented in a previous publication. By means of this procedure, a distribution of relaxation times, corresponding to Debye-like processes, is directly obtained from the dielectric data in the frequency domain. This method allows a straightforward comparison between our dielectric results and those previously reported from 2D-NMR measurements. The calculated distributions have a bimodal character, i.e., two different dynamical processes contribute to the whole dielectric α-relaxation of the blends. It is found that, although the faster process resembles to the PIP dynamics, the slower contribution involves the dynamics of both the PIP and PVE units. This fact explains the differences between the dielectric and nuclear magnetic resonance results.