New method of determining miscibility in binary polymer blends through hydrodynamic interaction: The free volume approach

Abstract

A new method has been developed to determine the probability of miscibility in binary polymer blends through hydrodynamic interaction. This is achieved by the measurement of the free volume content in blends of carefully selected systems-styrene acrylonitrile (SAN)/ poly(methyl methacrylate) (PMMA), PMMA/poly(vinyl chloride) (PVC), and PVC/polystyrene (PS)-with positron annihilation lifetime spectroscopy. The free volume content can predict the miscible/immiscible nature of the blends but provides no information on the extent of miscibility for different compositions of the blends. We have generalized a model used to understand the viscometric behavior of polymer/solvent systems to polymer/polymer systems through the free volume approach. This model provides two important parameters: a geometric factor (c) and a hydrodynamic interaction parameter (a). c depends on the molecular architecture, whereas a accounts for the excess friction at the interface between the constituents of the blend, and we propose that a can serve as a precursor to miscibility in a system and indicate which composition produces a high probability of miscibility. The efficacy of this proposition has been checked with measured free volume data for the three blend systems. The SAN/PMMA system produces a maximum a value of À209 at 20% PMMA; PVC/PMMA produces a maximum a value of À57 at 10% PMMA. Interestingly, for the PS/PVC system, a is close to zero throughout the entire concentration range. Therefore, we infer that a is perhaps an appropriate parameter for determining the composition-dependent probability of miscibility in binary blend systems.

A new insight into interface widths in binary polymer blends based on ortho‐positronium lifetime studies

“…Owing to the limitations of both DSC and inadequacy of the interchain interaction parameter, our group at this laboratory has developed a new method to determine the composition dependent miscibility level in binary polymer blends through hydrodynamic interaction approach making use of the same free volume data. 36,37 For polymers, viscosity is considered as an important property in understanding the viscoelastic behavior of polymers under stress and strain. 52 Conversely, the KRZ model is similar in theoretical conceptions of KSR model but brings in the concept of hydrodynamic interaction between the segments of the polymeric chains.…”

“…36,37,44,46 The free volume size is evaluated as V f ¼ (4/3)pR 3 . The fractional free volume or the free volume content (F v ) is calculated as…”

“…The above facts made us interesting to explore the possibility of the method developed recently based on positron lifetime spectroscopy, 36,37 its ability to provide information on the interface widths in dispersed binary polymer blends. As such, in this article, we describe procedure to obtain interface width or its dependence on composition in three dispersed polymer blends; one miscible namely SAN/PMMA and the immiscible blends namely PVC/PS and PVC/EVA with 3D morphology.…”

“…This data is used to derive hydrodynamic interaction parameter (a), a concept used for the first time by our group. 36,37 In brief, the concept of hydrodynamic interaction is as follows: the monomer units of dissimilar type in a binary blend produce friction at the interface which stems from the theory of hydrodynamic interaction. This is quantified to understand the behavior of interface regions due to factors like composition.…”

“…This concept was extended to polymer/polymer mixtures in solid phase. 36,37 In this work, the friction at the interface is quantified in terms of hydrodynamic interaction parameter (a) 36,37,40,41 derived from free volume data obtained from ortho-positronium lifetime measurement. DSC technique is used to supplement positron annihilation lifetime spectroscopy (PALS) results.…”