Rheology Of Immiscible Polymer Blends Research Articles

Predicting phase inversion based on the rheological behavior in Polyamide 6/Polyethylene blends

Models have been proposed to describe the rheology of immiscible polymer blends in relation to their morphologies, either for dilute droplet emulsions or for concentrated blends with complex interfaces. The morphologies obtained in reactively compatibilized blends are the result of a complex interplay between instabilities due to chemical reaction at interfaces and drop breakup and coalescence processes. We have studied reactively compatibilized Polyamide6/High Density Polyethylene (PA6/HDPE) blends with widely different viscosity ratios, obtained by changing the length of PA chains. The composition at phase inversion is shifted to high concentration of the most viscous component, as may be expected from simple rheological considerations. The relationships between the morphologies and the rheological behavior are discussed. The objective of this work is to relate the rheological behavior to the morphologies. Specifically, we show that phase inversion can be reasonably predicted, based on the rheological behavior of blends in the linear regime. This result could be of significant benefit for applications, since rheological studies are often easier to perform in the applicative context than electron microscopy observations, which are needed to characterize the morphologies at sub-micrometric scales.

Effect of fumed silica nanoparticles on the morphology and rheology of immiscible polymer blends

We examined the effect of interfacially active particles on the morphology and rheology of droplet/matrix blends of two immiscible homopolymers. Experiments were conducted on polybutadiene/polydimethylsiloxane (10/90) blend and the inverse system. The effects of fumed silica nanoparticles, at low particle loadings (0.1–2.0 wt%), were examined by direct flow visualization and by rheology. Fumed silica nanoparticles were found to significantly affect the morphology of polymer blends, inducing droplet cluster structure and decreasing the droplet size, regardless of which phase wets the particles preferentially. This is surprising in light of much past research that shows that particles are capable of bridging and thus induce droplet cluster structure in droplet/matrix systems only when they are preferentially wetted by the continuous phase. Therefore, there should exist other possible mechanisms responsible for these droplet cluster structures except for the bridging mechanism. We proposed a particle-flocculating mechanism based on the fact that fumed silica particles readily flocculate due to their high aspect ratio, fractal-like shape, or interparticle attractions. Optical microscopy also reveals that the clustering structure becomes more extensive, and the droplet sizes in the clusters become smaller when the particle loading is increased. Rheologically, the chief effect of particles is to change the flow behavior from a liquid-like rheology to gel-like behavior. This gel-like behavior can be attributed to droplet clustering. Moreover, it should be emphasized that such gel-like behavior can be seen in the blends regardless of which phase wets the particles preferentially, suggesting that, once again, bridging is not the only cause of droplet clustering.

Morphology and rheology of immiscible polymer blends filled with silica nanoparticles

The effect of silica nanoparticles on the morphology and the rheological properties of an immiscible polymer blend (polypropylene/polystyrene, PP/PS 70/30) was investigated. Two types of pyrogenic nanosilica were used: a hydrophilic silica with a specific surface area of 200m2/g and a hydrophobic silica having a specific surface area of 150m2/g. First, a significant reduction in the PS droplet volume radius, from 3.25 to nearly 1μm for filled blends with 3wt% silica, was observed. More interestingly, image analysis of the micrographs proved that the hydrophilic silica tends to confine in the PS phase whereas hydrophobic one was located in the PP phase and at the PP/PS interface (interphase thickness≈100–200nm). Furthermore, a migration of hydrophilic silica from PP phase toward PS domains was observed.An analysis of the rheological experimental data was based on the framework of the Palierne model, extended to filled immiscible blends. Due to the partition of silica particles in the two phases and its influence on the viscosity ratio, limited cases have been investigated. The rheological data obtained with the hydrophobic silica were more difficult to model since the existence of a thick interphase cannot be taken into account by the model. Finally, the hypothesis that hydrophilic silica is homogeneously dispersed in PS droplets and that hydrophobic silica is dispersed in PP matrix was much closer to the actual situation. It can be then concluded that stabilization mechanism of PP/PS blend by hydrophilic silica is the reduction in the interfacial tension whereas hydrophobic silica acts as a rigid layer preventing the coalescence of PS droplets.

Diffuse interface modeling of the morphology and rheology of immiscible polymer blends

A diffuse interface model is used to simulate a step-shear experiment of a binary immiscible polymer blend. The gradient theory used in diffuse interface modeling makes it possible to incorporate interfacial tension and governs the process of coalescence and breakup without any additional decision criteria. The interface tensor q, a direct outcome of the model, is used to relate microstructural information to the first-normal stress difference N1. The results obtained are in qualitative agreement with experiments reported in the literature.

Nonlinear rheology of immiscible polymer blends: Step strain experiments

Relaxation experiments after simple shear flow were performed on (50/50) PB/PDMS poly(1-butene)/polydimethylsiloxane immiscible model blends and the results were compared to the predictions of the Doi–Ohta and Lee–Park models. Three situations of flow were examined: (i) first the variation of stress relaxation was followed in time at various step strain amplitudes, (ii) variation of stress relaxation as a function of the amplitude of preshear rate at a fixed strain, and (iii) at a fixed strain and preshear rate, the relaxation of the stress was studied as a function of the time elapsed between the end of the preshear and the step strain. After application of step strains of various magnitudes, the stress relaxation modulus G(t,γ) at short times was found to obey the Wagner time-strain separability [Wagner (1976)]. It was possible to separate linear effects from the nonlinear ones via a damping function h(γ) of sigmoidal form. After cessation of steady shear flow of different magnitudes, the linear stress ...

Flow Induced Structure and Rheology of Immiscible Polymer Blends

Flow Induced Structure and Rheology of Immiscible Polymer Blends

Analysis of the morphology of polymer blends using ultrasound

Over recent years there has been great efforts towards the understanding of the rheology of immiscible polymer blends. It is now well accepted that their morphology, especially the concentration of the inclusions, their size, and their radii distribution, is a very important factor which controls their mechanical properties. The type of blend considered in this study is a polyamide/polypropylene system, in which the matrix is the polyamide (PA6) with inclusions of polypropylene (PP). Different concentrations have been used, as well as different surfactants. These blends give then rise to different acoustic properties, which have been characterized by measuring velocities of propagation and attenuation of ultrasonic waves during flow through a capillary rheometer. A wave propagation theory for viscoelastic emulsions was used to predict the values of the ultrasonic parameters as functions of the concentration, the radii distribution and the frequency when the thermophysical properties of the blend are known. We can therefore deduce the concentration and average size of inclusions, and then return to the morphology of the blends. Comparison with microscopic photographs seems to correlate well with our predictions. This method appears promising and could be used to differentiate between different blends during flow.