Static and dynamic studies of phase composition in a polydisperse system

We have conducted a study of the phase compositions of a ternary solution containing dextran/polyethylene glycol (PEG)/water using UV-visible spectrometry to study the equilibrium behaviour and confocal microscopy to study the dynamic behaviour observed when the system undergoes phase separation driven by the loss of water. Such a study of phase compositions using confocal microscopy is a new development of the technique. In the static experiments, we find a cloud curve, which lies above the coexistence curve on the PEG rich side of the phase diagram, this is found to be in qualitative agreement with calculations of the phase behaviour for a model polydisperse system. In the dynamic experiments, we are able to measure the phase composition using confocal microscopy in the late stages of separation. Here, the compositions lie well inside the coexistence curve at lower drying rates but converge with it at higher drying rates. This is linked to a change in phase morphology: at low rates, a droplet morphology is observed throughout the process whilst at high drying rates a gross phase separation into two layers is observed to occur even at the earliest times probed by the experiment.