Shear-induced demixing in a polystyrene/poly(vinyl methyl ether) blend: in-situ fluorescence and rheometry

Abstract

In miscible blends of polystyrene with poly(viny1 methyl ether), a shear-induced demixing occurs at temperatures as much as 40 K below the lower critical solution temperature. Demixing occurs at relatively low shear rates ranging from 1.5 to 4 s-l depending on the temperature and composition; the corresponding shear stresses and first normal stress differences range from 20 to 35 kPa and 30 to 120 kPa, respectively. There appears to be no threshold value of the shear rate or the shear stress for the onset, but a certain value of rate of work done on the sample roughly describes the steady-state demixing at a fixed temperature. When shear does induce demixing, some of the concentration differences are stable under shear for as long as 24 h. However, in other cases, a demixing appears for a shorter time, along with relatively high stresses, shortly after the inception of shear but disappears as the stresses drop at longer times. The time scale for the development of demixing ranges from hundreds to thousands of seconds and remixing after cessation of the flow typically occurs in thousands of seconds. Particularly at temperatures near the lower critical solution temperature, a substantial time is required for the stress development, even when there is no measurable demixing as indicated by fluorescence. Transmission electron microscopy on sheared samples confirms the presence of a shear-induced structure.

Investigation of the Dynamic Rheological Properties of a Polycarbonate Melt Presenting Solid-Like Characteristics and a Departure from Pure Liquid Newtonian Behavior at Long Relaxation Times

“…Mani et al [51] carried out step rate measurements on originally homogeneous polystyrene/polyvinyl methyl ether blends(PS/PVME) and observed, by simultaneous fluorescence measurements, that shear-induced demixing, producing segregation, can be triggered by a relatively low shear rate. Experimental evidence supports that both shearinduced mixing and shear-induced demixing, observed as suppression or enhancement of concentration fluctuations, respectively, can occur under a stress field depending on the amount of shearing and the molecular characteristics of the polymers: chemical affinity between the bonds being mixed, respective molecular weights and glass transition temperatures of the groups mixed.…”

Miscibility characterization of SMA/SAN and SMA/PMMA blends by differential scanning calorimetry and fluorescence techniques

“…Fluorescence quenching technique was also successfully used to study the effect of shearing on phase separation of PS/PVME blends. 17,18 For approximately identical weight contents of styrene, it was reported that SMA and SAN are miscible. [19][20][21][22][23] SMA/ SAN systems show the LCST behavior, which is determined by the characteristic single glass transition temperature (T g ) on the DSC curve.…”

Surface Micro‐Scale Semi‐Heterogeneous Structures in Compatible Polystyrene and Poly(vinyl methyl ether) Blend Thin Films Investigated by Lateral‐Force Microscopy

“…The compatible blends exhibit a lower critical solution temperature (LCST) phase diagram. Later, various aspects about this blend have been studied extensively, such as the polymer dynamics in blends, [3] phase-separation kinetics, [4] rheological properties, [5] shear-induced demixing, [6] the orientation and relaxation behaviors, [7] gas-transport properties, [8] thermal-or photo-oxidation, [9,10] and the influence of nano-fillers on the phase behaviors. [11] The real miscibility on the molecular or micro-scale level between these two components in macroscopic single-phase PS/PVME blends is, however, still under dispute.…”