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Phase transitions in polyelectrolyte systems

Jing Hua, University of Massachusetts Amherst

Abstract

We present a theory for polyelectrolyte systems: solutions and gels that allows the effective charge of the polymer backbone to self-regulate. Using a variational approach, we use an expression for the free energy of polyelectrolyte systems that accounts for all physically relevant contributions. This free energy is then minimized to predict the phase behavior of the system as a function of external variables such as temperature and salt concentration. In the first section, we present results for the phase separation of polyelectrolyte solution in salt-free solvents. We show that the daughter phases have different polymer charges from that of the mother phase. The critical point is also altered significantly by the charge self-regularization of the polymer chains. This work extends the progress made so far in the theory of phase separation of strong polyelectrolyte solutions to a higher level of understanding by considering chains which can self-regulate their charge. ^ In the second part, we present results for the volume phase transition of polyelectrolyte gels in salt-free solvents, solvents with monovalent salts, and solvents with divalent salts. The results of our theoretical analysis are in agreement with existing experimental results and also provide predictions for further experimentation. Our analysis highlights the importance of the self-regularization of the effective charge for the phase transition of gels in particular, and for charged polymer systems in general. Our analysis also enables us to identify the dominant free energy contributions for charged polymer networks and provides a framework for further investigation of specific experimental systems. ^ In the third part, we present results for the phase separation of polyelectrolyte solution in monovalent and divalent salty solvents. We tried some results for high volume fraction of the salt, those high salt calculation results will give us some ideas about the low temperature phenomena, however those results are un-physical. More calculations need to be done in order to discover the real physical range effects. It will cost more calculation hours, however it's doable based on the recent updated code.^

Subject Area

Physical chemistry|Polymer chemistry|Theoretical physics

Recommended Citation

Hua, Jing, "Phase transitions in polyelectrolyte systems" (2012). Doctoral Dissertations Available from Proquest. AAI3545940.
http://scholarworks.umass.edu/dissertations/AAI3545940

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