Lambient University

While dielectric analysis (DEA) has long been used in the composites industry, many companies could benefit from a more complete understanding of its potential uses and benefits. Lambient Technologies, the pioneers in dielectric analysis, are proud to present Lambient University - a course of free guidance to spread awareness of, and improve understanding about, DEA and its applications.

Lambient University is a guided course through the fundamentals of dielectric cure monitoring. The documents are brief and rigorous yet accessible, free of jargon and proceeding from basic concepts of DEA through practical guidance for making good measurements. They include clear figures, actual data, and real-world advice about how to use DEA - all written by the foremost experts in DEA, who have led the field for 40 years.

Through this series, we hope to foster connections with researchers and companies interested in testing and implementing DEA in labs and manufacturing environments.

Class 1A: Applications of DEA Dielectric cure monitoring, or dielectric analysis (DEA) takes its place among more conventional thermal analysis techniques like differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), and bridges the gap between laboratory and manufacturing environments.

Class 1B: Basics of Thermoset Cure The resins used in composites are thermosets, which polymerize then crosslink with the application of heat. These materials progress from a freshly mixed state (“A” Stage) to partially cured (“B” Stage) to fully cured (“C” Stage). The measurement of their changing electrical properties is the basis of dielectric cure monitoring.

Class 2A: Basics of Dielectric Measurements Dielectric cure monitoring uses electrical measurements of thermosets and composites to probe cure state. Data are interpreted with an model using capacitors and resistors derived from raw measurements of a sensor’s response voltage and/or current.

Class 2B: Loss Factor, Viscosity and Ion Viscosity The molecular structure of a material influences its capacitance, conductance and resistance, as well as the material properties of permittivity, loss factor and ion viscosity. The ability to probe viscosity before gelation and modulus after gelation gives dielectric cure monitoring the unique ability to monitor cure state from beginning to end.

Class 3A: Critical Points and Thermoset Cure The ion viscosity curve of a curing thermoset or composite can be characterized with Critical Points, which identify unique features of the data and allow comparison of the cure from test to test.

Class 3B: Linear vs. Logarithmic Scales From the beginning to end of cure the resistance or ion viscosity of a resin may increase by a factor of 100 or more from its minimum value. Plotting resistance on a logarithmic scale is the optimum method for seeing all the information available from dielectric measurements. 

Class 4A: Sensors, A/D Ratio and Base Capacitance As the scaling factor between resistance and ion viscosity, or capacitance and permittivity, the A/D ratio is important for determining dielectric properties from raw sensor measurements.

Class 4B: Comparison of Sensor Cure State Measurements With the correct A/D ratio, measurements with different sensors will have the same result, allowing flexibility in the choice and features of a sensor for cure monitoring.

Class 5A: Ion Viscosity and Temperature For the measurement of mechanical viscosity and cure state, ion viscosity provides valuable information from a simple electrical measurement. But ion viscosity also varies with temperature. So correct interpretation of ion viscosity requires knowledge of temperature at the time of measurement and an understanding of how temperature influences the data.

Class 5B: Electrode Polarization and Ion Viscosity Electrochemical effects in a thermoset or composite can distort data from low frequencies during early cure. Understanding electrode polarization and the boundary layer effect is important for avoiding confusion when the material is in the low viscosity state.

Class 6A: Choosing an Optimum Frequency for Cure Monitoring The correct choice of excitation frequency is necessary for good measurements of a material’s cure state, especially for determining the end of cure.

Class 6B: Equipment for Dielectric Cure Monitoring A dielectric cure monitoring system consists of a sensor, an instrument with AC excitation in the frequency of interest, a means of temperature measurement, as well as software to control repeated measurements during the cure.

Class 7A: Guidelines for Making Good Dielectric Measurements Some recommendations for successful dielectric cure monitoring.

Class 7B: Cure Monitoring of Sheet Molding Compound Bringing all the important concepts together in studying the cure of sheet molding compound (SMC).