title: Self-consistent field theory of polymer-ionic molecule complexation.
abstract: A self-consistent field theory is developed for polymers that are capable of binding small ionic molecules (adsorbates). The polymer-ionic molecule association is described by Ising-like binding variables, C(i) ((a))(kDelta)(=0 or 1), whose average determines the number of adsorbed molecules, n(BI). Polymer gelation can occur through polymer-ionic molecule complexation in our model. For polymer-polymer cross-links through the ionic molecules, three types of solutions for n(BI) are obtained, depending on the equilibrium constant of single-ion binding. Spinodal lines calculated from the mean-field free energy exhibit closed-loop regions where the homogeneous phase becomes unstable. This phase instability is driven by the excluded-volume interaction due to the single occupancy of ion-binding sites on the polymers. Moreover, sol-gel transitions are examined using a critical degree of conversion. A gel phase is induced when the concentration of adsorbates is increased. At a higher concentration of the adsorbates, however, a re-entrance from a gel phase into a sol phase arises from the correlation between unoccupied and occupied ion-binding sites. The theory is applied to a model system, poly(vinyl alcohol) and borate ion in aqueous solution with sodium chloride. Good agreement between theory and experiment is obtained.
authors.affiliation: Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L8, Canada. nakamur@caltech.edu
authors.forename: Issei
authors.initials: I
authors.lastname: Nakamura
authors.forename: An-Chang
authors.initials: AC
authors.lastname: Shi
mesh_terms: D000327:Adsorption; D001881:Borates / Q000737:chemistry*; D003198:Computer Simulation; D005782:Gels / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D044367:Phase Transition; D011142:Polyvinyl Alcohol / Q000737:chemistry*; D012965:Sodium Chloride / Q000737:chemistry; D012996:Solutions; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D001881:Borates; D005782:Gels; D007477:Ions; D012996:Solutions; D014867:Water; D012965:Sodium Chloride; D011142:Polyvinyl Alcohol