Dynamics and rheology of the morphology of immiscible polymer blends - on modeling and simulation (original) (raw)

Dynamic rheological analysis of a miscible blend showing strong interactions

Polymer, 2003

The rheological behavior of miscible blends was studied through oscillatory shear measurements. Two miscible blends were selected to compare with athermal blending cases, i.e. the hydrogen bonding poly(4-vinyl phenol)/poly(ethylene oxide) (PVPh/PEO) blend and the weakly interacting polystyrene/poly(2,6-dimethyl-1,4-phenylene oxide) (PS/PPO) blend. The homopolymers and the blends were characterized over a wide experimental window using the time-temperature superposition principle. The horizontal shift factor, a T , does not vary appreciably with composition for PS/PPO, whereas a strong compositional dependence is observed for the PVPh/PEO blends. Additions of up to 30 wt% of PEO to PVPh produce only minor changes in the value of rubber plateau modulus ðG 0 N Þ; while G 0 N increases steadily after this concentration. The G 0 N values follow athermal blending models [

Investigating the morphology/rheology interrelationships in immiscible polymer blends

Journal of Rheology, 2000

Morphological changes in immiscible polymer blends have been studied in shear flow using an original method based on quenching following deformation of molten samples Relaxation effects wete expected to be negligible during cooling and, hence, the real shear-induced blend microstructure could be analyzed The method has been successfully applied to follow morphological changes of immiscible blends composed of polystyrene and relatively high amounts of high-density polyethylene during creep experiments. The final steady-state morphology appeared to be intimately related to the applied shear stress and total deformation. Coalescence as well as large deformation and orientation of the dispersed phase panicles have been observed depending on the flow conditions The variations with time of the blend rheological properties and morphological observations are in qualitative agreement.

Theory of morphology evolution in mixtures of viscoelastic immiscible components

Journal of Rheology, 2005

An ellipsoidal model was constructed to describe the morphological evolution and rheological properties of a mixture of two immiscible viscoelastic components. The phenomenological parameters in the model were determined by comparing the interfacial velocity gradient with the viscoelastic theory for small deformation. The model was then applied to various model blend systems to predict the steady deformation, transient deformation, and relaxation after cessation of step shear flow. The model predictions were also compared with some available numerical simulations. The predictions on droplet deformation both in steady and transient regimes as well as the relaxation process were found to be in good agreement with the experimental results in literatures. The rheological properties predicted by the present model were also found to agree with the experimental results.

Dynamics of complex interfaces. I. Rheology, morphology, and diffusion

Chemical Physics, 2003

In this paper, we investigate, on two levels of description, the isothermal coupling: (i) between rheology and morphology in immiscible blends (A/B) and (ii) among rheology, morphology, and diffusion in mixtures consisting of an immiscible blend (A/B) and one simple fluid, s. The interface separating the phases A and B is described, on the kinetic level by an area density distribution function and on the mesoscopic level by a scalar and a traceless symmetric second order tensor. The nonlinear formulations are derived using the general equation for nonequilibrium reversible and irreversible coupling formalism which ensures the consistency of dynamics with thermodynamics. In addition to the non-Fickian character of mass transport, the coupled three-dimensional governing equations explicitly show the effects of the external flow and diffusion on the size and shape of the interface. New expressions for the stress tensor emerge naturally in the models including the contributions of the diffusion fluxes and the isotropic (Laplace) and anisotropic deformations of the interface. Asymptotic solutions of the governing equations also show that the transport coefficients (diffusivity, etc.) are explicitly dependent on the interfacial tension and on the velocity gradient of the applied flow. The latter dependence renders the process of mass transfer highly anisotropic even in the absence of internal stresses created by the deformation of the interface. The diffusion-free models of Doi-Ohta and Lee-Park are recovered as particular cases.

Rheology and morphology of concentrated immiscible polymer blends

Korea-australia Rheology Journal, 2001

The phase morphology is an important factor in the rheology of immiscible polymer blends. Through its size and shape, the interface between the two phases determines how the components and the interface itself will contribute to the global stresses. Rheological measurements have been used successfully in the past to probe the morphological changes in model blends, particularly for dilute systems. For more concentrated blends only a limited amount of systematic rheological data is available. Here, viscosities and first normal stress differences are presented for a system with nearly Newtonian components, the whole concentration range is covered. The constituent polymers are PDMS and PIB, their viscosity ratio can be changed by varying the temperature. The data reported here have been obtained at 287 K where the viscosities of the two components are identical. By means of relaxation experiments the measured stresses are decomposed into component and interfacial contributions. The conc...

The influence of matrix viscoelasticity on the rheology of polymer blends

Rheologica Acta, 2004

We examine the effects of matrix phase viscoelasticity on the rheological modeling of polymer blends with a droplet morphology. Two contravariant, second-rank tensor variables are adopted along with the translational momentum density of the fluid to account for viscoelasticity of the matrix phase and the ellipsoidal droplet shapes. The first microstructural variable is a conformation tensor describing the average extension and orientation of the molecules in the matrix phase. The other microstructural variable is a configuration tensor to account for the average shape and orientation of constant-volume droplets. A Hamiltonian framework of non-equilibrium thermodynamics is then adopted to derive a set of continuum equations for the system variables. This set of equations accounts for local conformational changes of the matrix molecules due to droplet deformation and vice versa. The model is intended for dilute blends of both oblate and prolate droplets, and droplet breakup and coalescence are not taken into account. Only the matrix phase is considered as viscoelastic; i.e., the droplets are assumed to be Newtonian. The model equations are solved for various types of homogeneous deformations, and microstructure/rheology relationships are discussed for transient and steady-state conditions. A comparison with other constrained-volume rheological models and experimental data is made as well.

Rheology of Miscible Blends: SAN and PMMA

Macromolecules, 1998

The linear viscoelasticity of miscible blends of a random copolymer of 80% styrene and 20% acrylonitrile and poly(methyl methacrylate) has been investigated using oscillatory shear. The Flory-Huggins interaction parameter of this blend is weakly negative. The glass transitions of the pure components are very close (∆T g) 20 K). The blends are thermorheologically simple, in that the oscillatory shear response at different temperatures can be superimposed with the empirical time-temperature superposition principle with a precision similar to that for the pure component polymers. These results are anticipated by a theory of concentration-fluctuation-induced dynamic heterogeneities in miscible polymer blends. While sizable concentration fluctuations are present in this blend system, they do not complicate the dynamics, because all compositions have similar local dynamics. We suggest a simple phase diagram based on this model, that should be useful for deciding whether time-temperature superposition will be valid for a given blend with weak energetic interactions. Regions of thermorheological complexity are separated from regions of thermorheological simplicity on a plot of the range of blend free volume studied against the glass transition contrast of the components (∆T g).