Impedance Spectroscopy of Reactive Polymers: Correlations with Chemorheology during Network Formation

Abstract

An investigation was carried out of correlations between dielectric, spectroscopic, and rheological properties during reactions in several epoxy/amine formulations of both polymer‐forming and nonpolymer‐forming nature. Dielectric results obtained from impedance spectroscopy were compared with results from near‐infrared spectroscopy, high performance liquid chromatography, and steady shear and dynamic mechanical measurements. Reaction kinetics obtained from dielectric, spectroscopic, and chromatographic results were in excellent agreement. Gelation and vitrification times of multifunctional formulations, determined by dielectric and rheological measurements, agreed surprisingly well, despite the empirical nature of such correlations. Nonetheless, a realization of the full potential of dielectric impedance spectroscopy in monitoring the progress of chemophysical changes in reactive polymers necessitates the development of fundamental scientific correlations between dielectric and chemorheological phenomena during cure.

Epoxy-Diamine Thermoset/Thermoplastic Blends: Dielectric Properties before, during, and after Phase Separation

“…This observation which is reported in the cure of neat TS by many authors over the past decade has led to the wide use of dielectric measurements of conductivity as an in situ means of monitoring the changing viscosity up to the vicinity of gelation. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] The current results strongly suggest that a major molecular mechanism for the conductivity in these pure epoxy-amine systems is a hydrogen bond exchange mechanism. They suggest that the slope of the conductivity-viscosity relation before phase separation and up to gel may be, in part, a function of the number and geometric structure of proton donor acceptor bonds in the monomers and the resulting chains.…”

“…9 Previously dielectric measurements have been used to monitor the changing viscosity and buildup in T g during polymerization of a variety of neat thermoset resins. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] This paper will address the ability of dielectric sensing to monitor these properties both before phase separation in the homogeneous solution and in each phase after the phase separation process. This paper will also discuss the ability of dielectric measurements to detect the onset of phase separation.…”

Morphological, chemical surface and electrical characterizations of lignosulfonate-modified membranes

“…Membrane electrical resistance was determined from impedance spectroscopy (IS) measurements, which were carried out with the membranes in contact with HCl solutions at different concentrations. IS technique is an excellent tool for characterization of membranes in such conditions since it allows the separation of membrane and electrolyte electrical contributions as well as the top layer and porous sublayer [19][20]. The determination of the membrane electrical parameters (resistance and capacitance) is made by analyzing the impedance plots by using equivalent circuits as models [21][22][23].…”

Microdielectric study of epoxy-amine systems: Gelation and relationships between conductivity and kinetics

“…Among these: -The inflexion point which appears in logarithm of conductivity vs. time curves was taken as the gel point [8][9][10][11] ; -The percolation model was applied to conductivity data to find the gel times [11][12][13][14][15][16][17][18] or conversion at the gelation threshold. For the second purpose, great effort was made to find equations relating: -conductivity with viscosity 6,8,9,20) ; -relaxed permittivity with degree of conversion 19,21) ; -relaxation time with viscosity 22) , glass transition temperature 32) or number of covalent bonds 18,23) ; -conductivity with glass transition temperature [24][25][26][27] ; -frequency of maximum loss with degree of conversion 28) ; -loss factor with number of covalent bonds 18,29) .…”