PEO/CHCl3: Crystallinity of the polymer and vapor pressure of the solvent - Equilibrium and non-equilibrium phenomena -

TL;DR

This study measures vapor pressures of chloroform/polyethylene oxide mixtures at 25°C to analyze crystallinity and solubility, revealing non-equilibrium effects influenced by film preparation methods and providing a thermodynamically consistent model.

Contribution

It introduces a new approach to model composition-dependent interaction parameters using only two adjustable parameters, linking vapor pressure data with crystallinity and solubility.

Findings

Vapor pressures vary with polymer crystallinity and film preparation.

Non-equilibrium phenomena significantly affect vapor pressure and solubility.

A thermodynamically consistent model with two parameters accurately describes the data.

Abstract

Vapor pressures were measured for the system chloroform/polyethylene oxide (peo, weight average molar mass = 1000 kg/mol) at 25 degrees centigrade as a function of the weight fraction w of the polymer by means of a combination of head space sampling and gas chromatography. The establishment of thermodynamic equilibria was assisted by employing thin polymer films. The degrees of crystallinity alpha of the pure peo and of the solid polymer contained in the mixtures were determined via dsc. An analogous degree of polymer insolubility, beta, was calculated from the vapor pressures measured in this composition range. The experiments demonstrate that both quantities and their concentration dependence are markedly affected by the particular mode of film preparation. These non-equilibrium phenomena are discussed in terms of frozen local and temporal equilibria, where differences between alpha and beta are attributed to the occlusion of amorphous material within crystalline domains. Equilibrium information was obtained from two sources, namely from the vapor pressures in the absence of crystalline material (gas/liquid) and from the saturation concentration of peo (liquid/solid). The thermodynamic consistency of these data is demonstrated using a new approach that enables the modeling of composition dependent interaction parameters by means of two adjustable parameters only.