Dielectric Study on the Heterogeneous Dynamics of Miscible Polyisoprene/Poly(vinyl ethylene) Blends:  Estimation of the Relevant Length Scales for the Segmental Relaxation Dynamics

Abstract

Dielectric study was performed on the polyisoprene (PI)/poly(vinyl ethylene) (PVE) miscible blends. We observed the end-to-end vector fluctuation dynamics (normal mode) of PI as well as the two R-relaxation processes corresponding to the segmental motions of PVE and PI. Among these three relaxation modes, the normal mode relaxation behavior was examined in detail. Since this relaxation reflects the dynamics of the length corresponding to the end-to-end distance of PI chain, comparison of the relaxation times for the normal mode and R-processes gives the information about the length scale of the two R-relaxation modes. We estimated the relevant length scales for the segmental motions in the blend and compared them with a single cooperative volume model and a dual length scale model. As a result, the latter model was found to describe better the features of the segmental dynamics in PI/PVE blends.

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.…”

“…Fig. 8 shows the plots of logðf ms =f 0 ms Þ versus DT g for blends of polyethers examined in this study and those reported so far [5,8,9]. It is noted that the blends reported in Refs.…”

“…It is noted that the blends reported in Refs. [5,8,9] exhibit bimodal loss curves. The values of DT g are larger than 70 K. On the other hand all blends examined here have exhibited unimodal loss curves for the segmental mode.…”

“…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].…”

Dynamics in miscible blends of polyisoprene and poly(p-tert-butyl styrene): thermo–rheological behavior of components

“…Extensive studies have been conducted for such miscible blends to examine the dynamics of monomeric segments being related to the glass transition. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Those studies revealed characteristic features of the miscible blends such as the broad (almost two-step) glass transition noted in thermal measurements, the broad modes of segmental motion detected with NMR, and the broad and thermo-rheologically complex relaxation processes observed with the dielectric/viscoelastic methods. These features are related to the self-concentration effect 16 and the local composition fluctuation.…”