Rheological And Dielectric Characterization of Thermosetting Polymers. Jeffrey Gotro, Ph.D.

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1 Rheological And Dielectric Characterization of Thermosetting Polymers

2 Outline Introduction Oscillatory parallel plate rheometry Dynamic dielectric measurements Simultaneous dynamic mechanical/dielectric measurements In-situ cure monitoring Summary

3 Everything flows Rheology The observed properties depend on the timescale of the deformation Glass Newtonian Liquid Polymer melts are called memory fluids Properties depend on the deformation history Memory fluids exhibit both liquid-like and solid-like properties Hence the term Viscoelasticity

4 Viscoelasticity of Polymer Melts Short deformation times lead to elastic solid behavior Deformation at a constant rate for a time which is long compare to the memory time (relaxation time) leads to viscous behavior Think about Silly Putty How does it deform at short times? Does it flow?

5 Thermoplastics versus Thermosets Thermoplastics -polymer chains not linked together -reprocessible by melting Thermosets -polymer chains are crosslinked -cannot be reprocessed Rheology of thermosetting polymers is determined by the curing conditions

6 Parallel Plate Geometry For small strain amplitude, timeindependent polymers (linear viscoelastic regime): σ = γo[g' sin ( ω t) + G" cos ( ω t)] Plates enclosed in temperature-controlled oven for curing studies

7 Oscillatory Rheometry γ = γο sin ( ωt) σ = σosin ( ω t + δ ) δ Time Measure both elastic and viscous components

8 Evolution of Viscosity during Cure

9 Dynamic Moduli During Curing Elastic Viscous Loss is viscous component, Storage is elastic component of the complex modulus

10 Viscosity at Several Heating Rates Epoxy-based resin Minimum viscosity and width of the flow window depend on heating rate

11 Viscosity and Conversion During initial softening, the conversion remains constant

12 Black Box View

13 Analogous to Dynamic Mechanical but Excite With Time-Dependent Voltage

14 Dynamic Dielectric Measurements

15 Definitions Dielectric Permittivity: Represents the polarization of the medium Typically called the dielectric constant, but for curing systems, the dielectric constant changes as a function of temperature and cure state Dielectric Loss Factor: Arises from two sources Energy loss associated with time-dependent dipolar relaxations Bulk (ionic) conduction

16 Dielectric Loss Factor σ ε" = + ε π εο 2 f " d σ = i qi N i µ i q = charge magnitude N = number of species per unit volume µ is the ion mobility

17 Dielectric Sensor Geometry

18 Dielectric Sensor Embedded in Plates Simultaneous measurement of dielectric and dynamic mechanical response

19 Simultaneous Measurements Input Overload Loss Factor Complex Viscosity

20 Dielectric Loss Factor

21 Dipolar Relaxations at Tg

22 Dipolar Relaxations During Vitrification

23 Full Loss Factor Spectrum During Curing Frequency dependent dipolar relaxations Tg is higher than the cure temperature, vitrification occurs during heating

24 Similar Profile for Epoxy Resin Magnitude of the ionic conductivity governed by the frequency

25 In-situ in Lamination Stack Embed dielectric sensor in lamination stack to measure cure profile

26 Dielectric Profile During Lamination Heating rate influences rheology, cure-path independent

27 Loss Factor Correlated to Viscosity

28 Summary Chemorheology of thermosetting polymers can be investigated using: Dynamic Oscillatory parallel plate rheometry Dynamic Dielectric measurements Simultaneous dynamic dielectric and dynamic mechanical measurements provide detailed insight into the physical changes during curing In-situ dielectric measurements can be used as cure monitors during the processing of thermosetting polymers

29 Contact Us InnoCentrix, LLC Antonio Parkway, Suite B Rancho Santa Margarita, CA Bus: (949) Bus: (877) 88-POLYMER ( )

Lecture 7: Rheology and milli microfluidic

Lecture 7: Rheology and milli microfluidic 1 and milli microfluidic Introduction In this chapter, we come back to the notion of viscosity, introduced in its simplest form in the chapter 2. We saw that the deformation of a Newtonian fluid under