Cylindrical cell model for the electrostatic free energy of polyelectrolyte complexes

P.M. Biesheuvel, M.A. Cohen Stuart

    Research output: Contribution to journalArticleAcademicpeer-review

    50 Citations (Scopus)

    Abstract

    Associative phase separation (complex coacervation) in a mixture of oppositely charged polyelectrolytes can lead to different types of (inter-)polyelectrolyte complexes (soluble micelles, macroscopic precipitation). In a previous report [Langmuir 2004, 20, 2785-2791], we presented a model for the electrostatic free energy change when (weakly charged) polyelectrolyte forms a homogeneous complex phase. The influence of ionization of the polymer on the electrostatic free energy of the complex was incorporated but the influence of complex density neglected. In the present effort, cylindrical cells are assumed around each polyelectrolyte chain in the complex, and on the basis of the Poisson-Boltzmann equation, the electrostatic free energy is calculated as a function of the complex density. After combination with Flory-Huggins mixing free energy terms and minimization of the total free energy, the equilibrium complex density is obtained, for a given ratio of polycations to polyanions in the complex. The analysis is used in an example calculation of polyelectrolyte film formation by alternatingly applying a polycation and a polyanion solution. The calculation suggests that the often observed exponential growth of a polyelectrolyte film when the polymer is weakly charged has a thermodynamic origin: the polyelectrolyte complex shifts repeatedly between two equilibrium states of different densities and compositions. However, when the polyelectrolytes are strongly charged the difference in the compositions between the two equilibrium states is very small, and exponential growth by an absorption mechanism is no longer possible.
    Original languageEnglish
    Pages (from-to)4764-4770
    JournalLangmuir
    Volume20
    Issue number1
    DOIs
    Publication statusPublished - 2004

    Keywords

    • electrical double-layer
    • exponential-growth
    • multilayers
    • equilibria
    • binding
    • charge
    • force
    • films
    • salt

    Fingerprint Dive into the research topics of 'Cylindrical cell model for the electrostatic free energy of polyelectrolyte complexes'. Together they form a unique fingerprint.

    Cite this