Predicting phase behavior of multi-component and polydisperse aqueous mixtures using a virial approach

Luka Sturtewagen

Research output: Thesisinternal PhD, WU


In this thesis we aimed to get a better understanding of the phase behavior of polydisperse and multi-component mixtures in solution. We approached this in a systematic way, starting with model systems of hard spheres and ending with a system of polydisperse macromolecules.

In Chapter 1 we presented a short overview of the available literature on polydisperse en multi-component mixtures that show segregative phase separation.

In Chapter 2 we reviewed the theory of interactions in systems of a solute component in a solvent based on the second virial coefficient. The theory was expanded to allow for multiple distinguishable types of solute components. This chapter describes the general equations used in the thesis that define the phase boundary, stability of the mixture, and critical point. Next to the theory, the chapter also dealt with the effect of polydispersity on the phase behavior of a binary mixture of additive hard spheres. This chapter showed that the largest species in the polydisperse component had the largest influence on the changes in the phase diagram.

In Chapter 3 we deal with the effect of non-additivity on the phase behavior of a binary mixture of hard spheres with slight polydispersity or impurities. Non-additivity between the two polydisperse and monodisperse component shifts the phase boundary to higher (negative non-additivity) or lower (positive non-additivity) concentrations. Negative non-additivity within a polydisperse component decreased overall compatibility and lowered the phase boundary. Positive non-additivity within a polydisperse component pushed the two-phase boundary to slightly higher concentrations and made three-phase demixing possible.

In Chapter 4 we discussed the influence of a third component added to a binary mixture that is incompatible. When the third component is compatible with both binary components, the phase boundary is not altered and upon demixing, the third component is present in both phase in similar amounts as in the parent mixture. When the third component is incompatible with one of the other two components, the phase boundary bends towards the axis-plane. Upon demixing, the third component preferentially goes to the phase enriched in the component with highest relative compatibility. When the third component is incompatible with both, three-phase demixing becomes possible.

In Chapter 5 we applied the gained knowledge from the model systems to a binary mixture of the polydisperse polymers polyethylene glycol and dextran. The phase behavior of the macromolecules was theoretically predicted, taking their experimental osmometric second virial coefficients and size polydispersity into account, and compared to the previously published experimental phase diagram. Taking polydispersity into account allowed for a better prediction of the experimental phase boundary compared to assuming monodispersity.

In Chapter 6 we discussed our results from the different chapters and placed the current work in a wider context of the available scientific literature, and discuss future research on multi-component and polydisperse mixtures in solution.

In conclusion, the virial approach we used has yielded results in line with previous theoretical and experimental work on polydisperse mixtures and mixtures of more than two components, and at the same time allows for direct experimental testing of the theoretical approach using virial coefficients directly obtained from membrane osmometry.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • van der Linden, Erik, Promotor
  • van Mil, H.G.J., Co-promotor, External person
Award date11 Nov 2020
Place of PublicationWageningen
Print ISBNs9789463953771
Publication statusPublished - 11 Nov 2020


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