Analysis of the Glass Transition Behavior of Polymer−Salt Complexes:  An Extended Configurational Entropy Model

Abstract

A new molecular thermodynamic model is developed of the glass transition temperatures (T g) of binary polymer−salt complexes by combining configurational entropy theory with Guggenheim's form of the Debye−Hückel theory. The interactions between the polymer chains and the salt as well as those between cations and anions are accounted for by this model. The predictions of this extended configurational entropy theory are compared with the T g values of poly(2-ethyl-2-oxazoline) (POZ) complexed with AgBF4, AgClO4, AgCF3SO3, and AgNO3 at various compositions, as obtained by differential scanning calorimetry (DSC). The model accurately predicts the experimental T g values even at high concentrations of silver salt (i.e., up to a mole ratio of [Ag]/[CO] = 1/1), where the deviation of the simple configurational entropy theory from experimental data is large. Moreover, the maximum in the glass transition temperature, i.e., the increase in T g with salt concentration at low salt concentrations but its decrease at high salt concentrations, is explicable with this model.

Effect of salt concentration on the glass transition temperature and ionic conductivity of poly(ethylene glycol)-polyurethane/LiClO4 complexes

“…Accordingly, the interaction between polymer chains and salt may be weakened, thereby yielding the decrease in T g (or increases in chain mobility) of polymer-salt complexes at high salt concentrations. 16,17 On the other hand, as a preliminary step for the ensuing rheological study on polymer/salt complex electrolytes, dynamic T g 's were measured on pure PEG-PU and PEG-PU/LiClO 4 complex samples under the condition of small oscillatory strain amplitudes by using DMTA. Figure 3 shows the temperature dispersions of loss tangent, tan δ = E"/E' (where E' and E" are storage and loss tensile moduli, respectively), for PEG-PU/LiClO 4 complexes of different salt contents at a frequency of 1 Hz.…”

“…However, at high salt concentrations the decrease in T g (or increase in chain mobility) of complexes may arise from the increased d spacing due to the electrostatic repulsion between anions, and from the decreased interaction between polymer chains and salts owing to the formation of ion pairs and/or higher order ion aggregates. 16,17 In this work, we studied the effects of salt content on the ionic conductivity and T g for poly(ethylene glycol)-polyurethane (PEG-PU)/LiClO 4 complex electrolytes prepared by the solvent casting method using a.c. impedance spectroscopy, differential scanning calorimetry (DSC) and dynamic mechanical thermal analyzer (DMTA). Comparison between thermal T g (by DSC) and dynamic T g (by DMTA) at different salt contents was also made for reference.…”

Silver polymer electrolyte membranes for facilitated olefint transport: carrier properties, transport mechanism and separation performance

“…This trend is in a good agreement with an extended configurational entropy theory as follows. 40,41 (…”

“…A diss is the Debye-Hückel coefficient, representing the strength of the interaction between cation and anion. 41 The increase in T g upon addition of metal salts is primarily attributed to both the transient cross-links of polymer segments and the dangling of metal salts on the chain. The solid lines in Figure 4 were obtained from eq.…”

Supramolecular Functionalities Influence the Thermal Properties, Interactions and Conductivity Behavior of Poly(ethylene glycol)/LiAsF6 Blends

“…good correlation exists between the experimental data and the model's predictions for both the U-PEG and U-PEG-U systems at relatively low lithium salt contents. Larger deviations appeared at higher lithium salt contents; in this case, however, the value of A DH should be constant in the U-PEG and U-PEG-U systems, because they feature the same lithium salt [31]. Nevertheless, if we take into account only the strength of the interaction parameter, that for the lithium salt/U-PEG-U blend (r 12 = 2.7; A DH = 0.02) would be greater than that for the lithium salt/U-PEG blend (r 12 = 2.6; A DH = 0.02), indicating that the stronger interactions are those between the lithium salt and U-PEG-U.…”