Size‐Dependent Interfacial Tension of Polymer Blends with Broad Composition Polydispersity

Abstract

The surface tension as a function of system size of a pure blend with chemically polydisperse compatibilizer is investigated by simulation. The main finding is that such compatibilizers adsorb readily at the interface between the bulk phases giving rise to very broad interfacial zones. This phenomenon leads to a marked size dependence of the interfacial tension. However the adsorption only leads to a decrease of 40% of the interfacial tension of the blend without compatibilizer. The limited effect on interfacial tension is explained by the observation that a considerable fraction of the compatibilizing chains do not contribute to the interfacial tension, instead these chains become part of an inhomogeneous phase with extensive thermodynamic properties.magnified image

Phase Evolution Theory for Polymer Blends with Extreme Chemical Dispersity: Parameterization of DDFT Simulations and Application to Poly(propylene) Impact Copolymers

“…A full analysis is given in a recent publicatation, [34] that contains numerical and theoretical investigation of the interfacial profiles. Here, we will note that in first order approximation the surface tension is roughly same as that between a neat PE and PP phase.…”

“…The Fourier transform of the dynamical equation in the linear regime reads [see Equation (34)] For the spinodal analysis the spectrum of the kinetic factor is irrelevant. The dynamical equations are solved by Crank-Nicolson time-iteration on a grid of mesh size h, using a finitedifferencing method.…”

Morphology formation in polypropylene impact copolymers under static melt conditions: A simulation study

“…Although for interfaces in simple two‐phase systems the interfacial tension is a clearly defined and useful quantity, it is less obvious how to define interfacial tension for multicomponent mixtures that have very broad interfaces. We have designed a procedure that permits the calculation of interfacial tension in systems featuring broad interfaces 33. In short, the procedure involves successive simulation of a system with increasing droplet size keeping the average density of each component exactly the same.…”

“…We have designed a procedure that permits the calculation of interfacial tension in systems featuring broad interfaces. 33 In short, the procedure involves successive simulation of a system with increasing droplet size keeping the average density of each component exactly the same. A plot of the equilibrium free energy per grid point against the inverse system size allows to derive the interfacial tension from the (local) slope.…”

“…The units consist of bead diameter and the box is subject to reflecting boundary conditions. In a recent paper, we argued the validity of using a 1D approach as compared with the computationally more demanding 3D approach, as long as in the simulation of a real system, proper care is taken to adjust for the shell thickness 33…”