Dynamic dielectric analysis: Nondestructive material evaluation and cure cycle monitoring

Abstract

Dynamic dielectric analysis (DDA) has been used to study curing polymer systems and thermoplastics. Measurements have been made over a frequency range of six decades. This wide range of frequencies increases the amount of information which can be obtained. The data is analyzed in terms of the frequency dependence of the complex permittivity ε*, specific conductivity σ(ohm−1 cm−1), and the relaxation time τ, parameters which are characteristic of the cure state of the material and independent of the size of the sample. Dynamic dielectric measurements have been used to monitor polymer processing in UDEL‐P1700, LARC‐160, polyphenyl quinoxaline (PPQ), and Epon 828 cured with Agent U. Dynamic dielectric measurements have been correlated with viscosity for the polysulfone thermoplastic UDEL‐P1700 and with viscosity and ultrasonic measurements on the DGEBA type epoxy Epon 828 cured with Agent U. The experimental results suggest that when ionic processes dominate the dielectric response, the intensive property σ is a good monitor of the resin's viscosity. The results show that the dielectric relaxation time τ can be used to monitor the state of the system and the extent and rate of the reaction. Solvent evolution can also be easily observed.

Liquid crystalline polymer networks based on a nematic epoxy resin with azoxy group

“…The appli− cation of the DS technique for observation of thermosetting systems was first described by Senturia and Sheppard [16]. The procedure of dielectric monitoring of curing of various systems, including epoxy−amine ones, was developed and is continually improved by other researchers [17,18]. The main subject of those studies was focused on changes in the dynamics of dipolar motions in the course of the reaction.…”

Simultaneous kinetic and microdielectric studies of some epoxy-amine systems

“…11,16 -18 Then, great efforts have been made to establish relationships between conductivity and viscosity, 5,12,13,18 conductivity and glass transition temperature [7][8][9][10]18 in order to obtain models that can be used in intelligent processing. The cure index was also compared with the degree of conversion of epoxy groups.…”

Dielectric analysis of depth dependent curing behavior of dental resin composites

“…Initial ion viscosity, ̅ , (MΩ cm) 161 (10) 162 (4) 171 (4) 184 (10) 198 (19) 185 (7) 196 (9) Slope of the linear range, ̇ , (MΩ cm/s) 460 (33) 295 (46) 218 (9) 164 (10) 131 (13) 66 (6) 58 ( (4) 76 (3) 88 (7) 90 (7) 98 (9) 103 (2) 95 (6) Slope of the linear range, ̅ (MΩ cm/s) 236 (22) 177 (15) 155 (22) 118 (11) 83 (15) 68 (4) 36 (7) Average ion viscosity between 37 and …”

“…Another method to monitor the curing behavior of resins is the dielectric analysis (DEA) which is widely used in composites manufacturing in the aircraft industry [29][30][31][32][33][34], but hardly established in dental science. In some cases it has been applied for the frequency dependent evaluation of dielectric properties in certain states of cure but without tracking the light-curing process itself in a suitable time-resolution [3,35,36].…”