Concentration Fluctuations and Nanosegregation in a Simplified Industrial Blend with Large Dynamic Asymmetry

Abstract

Applying small-angle neutron scattering (SANS) on isotopically labeled samples, we have characterized the thermally driven concentration fluctuations (TCFs), one of the main factors in the phenomenology of blend dynamics, in mixtures of styrene−butadiene rubber (SBR) and oligomers of polystyrene (PS) with different compositions. This system displays a large dynamic asymmetry and is thus a good model to explore the tunability of properties of interest in the rubber industry. The SANS experiments, complemented with neutron diffraction with polarization analysis, have allowed one to determine the UCST behavior of the blend and establish its phase diagram. We find a close vicinity of the spinodal and vitrification lines for intermediate concentrations and samples rich in PS. This induces the freezing of the correlation length for TCF when decreasing the temperature and also has an impact on the reported dielectric response of these mixtures. Furthermore, we have deduced the relevant length scale for segmental relaxation from the comparison of SANS and dielectric results. The values found (≈1.5−2 nm) are close to the Kuhn lengths of the components. The relevance of nanometric length scales in this system could also be tentatively attributed to an underlying nanodomain structure associated with the segregation of phenyl rings and main chains, supported by complementary X-ray diffraction experiments.

Rigidity of plasticizers and their miscibility in silica‐filled polybutadiene rubber by broadband dielectric spectroscopy

“…The broadening effect of the α‐relaxation increases with increasing content of miscible plasticizer. This is a typical phenomenon assumed to be originating from thermally driven concentration fluctuations 37–41 . In contrast to the shift of the α‐relaxation peak, the β‐relaxation appears unaffected in the frequency domain by the variation of the plasticizer.…”

“…The broadening of the α‐relaxation peak is expected to be caused by concentration fluctuations between polybutadiene and the plasticizer as miscible components 37–39 . These concentration fluctuations increase with increasing concentration of the plasticizer in case of miscible blends, while immiscible blends show two separated relaxation peaks with less additional broadening due to less concentration fluctuations 12,37 .…”

“…Thus, less concentration fluctuations are expected to take place in the 80 phr IC compound compared to the 80 phr AMS compound. This reduction in concentration fluctuation might result from a phase separation of IC from polybutadiene, as the fluctuations take place in a small environment next to the polymer chain segments 39 …”

Disentangling the Calorimetric Glass-Transition Trace in Polymer/Oligomer Mixtures from the Modeling of Dielectric Relaxation and the Input of Small-Angle Neutron Scattering

“…The value obtained for the relevant length scale, ∼25 Å, is close to that deduced by us in a recent work on blends of the same PS-oligomers and a lower molecular weight SBR of different microstructure, invoking the same framework. 31 Thus, as the respective self-concentration parameters of the components were taken as concentration independent, the number of free parameters accounting for blending effects involved in the BDS description is, effectively, only three: φ self SBR , φ self PS , and 2 R c . Despite the various assumptions and simplifications involved in our approach, the parameter values we obtained are in the range one could expect on the basis of the fundamental understanding of the polymer segmental dynamics.…”

“…The scattering length density ρ (scattering length of the monomer divided by the monomeric volume) of SBR was calculated to be ρ SBR = 8.50 × 10 9 cm –2 . In the case of PS, which is deuterated but not 100%, the scattering length density was experimentally determined in a previous work 31 (ρ PS = 59.25 × 10 9 cm –2 ). We note that the values of some parameters as the effective monomer volume or the scattering length density are specific for the particular materials here investigated, since they depend on the microstructure, molecular weight, and isotopic labeling considered.…”