Segmental Dynamics in Poly(vinylethylene)/Polyisoprene Miscible Blends Revisited. A Neutron Scattering and Broad-Band Dielectric Spectroscopy Investigation

Abstract

Despite the great experimental effort carried out over the past years by means of different techniques, the segmental dynamics in the model blend system poly(vinylethylene)/polyisoprene (PVE/ PI) is still a topic of strong debate. One of the most controversial questions is the possibility of a bimodal distribution of segmental relaxation times for polyisoprene in the blend. In this work, we have combined a microscopic technique, quasielastic neutron scattering (QENS), with molecular isotopic labeling and broad-band dielectric spectroscopy. The measurements have been carried out on the same samples and at the same temperature (270 K). By means of this combination, we have shown that all the PI in the miscible blend sample PVE/PI (50 wt % PVE-50 wt % PI) dynamically behaves very close to pure PI. In contrast, the R-relaxation of PVE component in the blend is drastically "plasticized". In addition, it has been shown for the first time by QENS that the secondary -like processes seem not to be modified by blending, at least for the blend component displaying the higher T g. These experimental facts contradict many of the results previously published about the dynamics of the PI/PVE system, and as far as our knowledge, they cannot be explained in the frame of the models presently available for polymer blends dynamics.

Dielectric study of dynamical heterogeneity in blends of polyethers

“…However, Alegria et al [2] found that miscible blends of cis-polyisoprene (PI) and poly(vinyl ethylene) (PVE) exhibit bimodal dielectric loss curves for the local segmental relaxation (a relaxation). Similar dielectric behavior was observed for polymer blends in which the difference of glass transition temperatures T g of the components is larger than 70 K [3][4][5][6][7][8][9][10]. Hereafter the term 'bimodal' means that a loss curve clearly exhibits two peaks or a main peak and a shoulder.…”

“…Hereafter the term 'bimodal' means that a loss curve clearly exhibits two peaks or a main peak and a shoulder. Dynamic heterogeneity has been investigated by using various methods such as dielectric spectroscopy, [3][4][5][6][7][8][9][10] rheology, [11] and NMR [12][13][14] in which, distinct segmental dynamics of the components were observed as the fast and slow modes. Such a behavior of distinct dynamics has been also known for polymer/diluent systems [15,16].…”

Cause of the fragile-to-strong transition observed in water confined in C-S-H gel

“…6 Moreover, a comparison between dielectric and QENS relaxation times can be made since it is well-established that the time scale deduced from neutron scattering at a momentum transfer Q of about 0.9 Å −1 is comparable with that obtained by dielectric spectroscopy. 38,39 As seen in Figure 2 Below 210 K, the relaxation times are fitted by the Arrhenius equation,…”

Relationship between the α‐ and β‐relaxation processes in amorphous polymers: Insight from atomistic molecular dynamics simulations of 1,4‐polybutadiene melts and blends

“…Dielectric measurements on such blends reveal significant dielectric loss at high frequency that exhibits weak concentration dependence and is located in a frequency range similar to the response of the neat melt of the lower T g component as illustrated in Figure 13 for a polyisoprene(PI)/poly(vinylethylene) (PVE) blend. 26 For polymer blends such as polystyrene/poly(methyl phenyl siloxane) 27 or polystyrene/poly(vinyl methyl ether), 28,29 where the T g difference between the component polymers is greater than 80 8C, dielectric spectroscopy has clearly showed two distinct relaxations of the fast component where one relaxation was found to have a relaxation time similar to that of the neat melt of the fast component and another closer to that expected based upon blend-average dynamics. Several theoretical models attempt to explain dynamical behavior of blends and their components based on thermally driven concentration fluctuations, 30 chain connectivity, 31 or a combination of both.…”