WLF (Williams-Landel-Ferry) Dependence of the Dielectric Properties of DGEBA (Diglycidyl Ether of Bisphenol-A) Epoxy Resins
Abstract
The frequency and temperature dependence of the complex dielectric constant (Epsilon) of seven diglycidyl ether of bisphenol-A (DGEBA) epoxy resins having epoxide equivalent weights (EEW) in the range 175 to 1880 have been measured from T subscript -30 C to T subscript + 70 C at frequencies between 0.1 and 10,000 Hz. In the vicinity of T subscript g, Epsilon is dominated by dipole relaxation, while at higher temperatures ionic conductivity dominates. For all resins, the temperature dependences of the frequency of maximum dipole loss, fmax, and of the conductivity, sigma, obey the Williams-Landel-Ferry (WLF) equation. The WLF constants C subscript 1 and C subscript 2 were determined for both the fmax and sigma data for each of the resins. In a given material, the WLF constants for sigma and fmax differed, indicating that the temperature dependences of the mobilities of ionic impurities and permanent dipole moments differ quantitatively. As the EEW of the material increased, the C subscript 1 values determined for the conductivity at high EEW's, while the corresponding C subscript 2 constants decreased slightly. Free volume and entropic theories of the glass transition are used to interpret these results in terms of the underlying conduction and dipole relaxation processes.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 23, 1985
- Accession Number
- ADA159224
Entities
People
- N. F. Sheppard Jr.
- S. D. Senturia
Organizations
- Massachusetts Institute of Technology