Effect of Free-Volume Hole Fraction on Dynamic Mechanical Properties of Epoxy Resins Investigated by Pressure–Volume–Temperature Technique

Abstract

Dynamic mechanical analysis experiments were carried out to investigate the mechanical properties of four types of chemically different epoxy resins. Pressure−volume−temperature (PVT) experiments were performed to determine the free-volume hole fraction (h PVT ) of each epoxy resin using the Simha−Somcynsky lattice−hole theory. Using the Williams− Landel−Ferry equation, the correlations between the relative hole fraction (1 − h PVT T r /h PVT , where h PVT T r is the hole fraction at a reference temperature T r ) and four typical parameters reflecting dynamic mechanical properties [storage modulus (E′), loss modulus (E″), damping factor (tanδ), and complex viscosity (|η*|)] were studied in the temperature range from T g(PVT) (the glass transition temperature determined by PVT data) to T g(PVT) + 100 °C. In the temperature range from T g(E onset ′ ) (temperature corresponding to the intersection of the two tangent fitting lines in the E′(T) curve indicating the glassy-state and glass-transition stages) to T g(PVT) + 100 °C, the variations in the four dynamic mechanical parameters with a relative hole fraction could be separated into two distinct categories: (i) log[E′(T)] and log[|η*|(T)] decreased linearly to their minimum values and then remained nearly unchanged with increasing relative hole fraction, and (ii) log[E″(T)] and log[tanδ(T)] first increased monotonically to their maximum values and then decreased linearly with the increasing relative hole fraction. This study demonstrates that the PVT technique is a feasible and reliable experimental method to determine the hole fractions of thermoset polymers.

Gas permeation and microstructure of reduced graphene oxide/polyethyleneimine multilayer films createdviarecast and layer-by-layer deposition processes

“…The free volume theory posits that gas molecules in polymers can migrate only when surrounded by large enough free volume holes. [68][69][70][71][72][73][74][75][76][77][78][79] Thus, it is of primary importance to analyze the gas permeation within the free volume in PEI/RGO composite lms. Aer all other measurements had been completed, the PEI/RGO composite lms were carefully scraped off the substrate, and the resulting powder-like PEI/RGO composites were mechanically pressed to discs for PALS measurement.…”

“…84 As the free volume theory makes clear, the permeability of gas molecules in polymers is sensitive to the size, density, and distribution of free volumes, as well as the fraction free volume. [71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] Moreover, the size, solubility, and weight of the gas molecules also have a signicant inuence on their permeation. [44][45][46] Thus, gas permeation in polymer is a very complex phenomenon, and there is rarely a simple linear relation between the gas permeability and a given parameter.…”