Dielectric Thermal Analysis Duncan Price IPTME, Loughborough University © Copyright: (2006)

contents  Equipment  Thermally stimulated current analysis  Theory  Example – multi-frequency temperature sweep  Time-temperature superposition  Applications

equipment

dielectric relaxation

thermally stimulated current analysis

voltage-current relationship in a capacitor

theory The admittance of the sample (Y) given by: Y = / Y is a vector quantity and is characterised by its magnitude |Y| and direction . Capacitance (C) is the ability to store electrical charge and is given by: C = |Y| sin(  )/  Conductance (G) is the ability to transfer electric charge and is given by: G = |Y| cos(  )

theory (contd.) Data are presented in terms of the relative permittivity (ε’) and dielectric loss factor (ε”) – these are related to capacitance and conductance by: ε’ = C/(ε 0.A/D) & ε” = G/( .ε 0.A/D) where ε 0 is the permittivity of free space (8.86× F m -1 ) and A/D (in m), is the ratio of electrode area (A) to plate separation or sample thickness, D for a parallel plate capacitor. ε’ & ε” are dimensionless quantities. The ratio ε”/ε’ is the amount of energy dissipated per cycle divided by the amount of energy stored per cycle and known as the dielectric loss tangent or dissipation factor (tan  ).

poly(ethylene terephthalate)

 ’ vs. frequency

master 130°C

Arrhenius plot

self adhesive film

base film

in-situ photodegradation monitoring Dielectric loss factor,  ” (0.1 Hz) for adhesive with different stabiliser packages during accelerated weathering Sample“standard”“poor”“good” initial after 600 hr after 1200 hr

online cure monitoring

dielectric thermal analysis of water in pores

summary  Similar to TMA/DMTA  Very sensitive for polar/ionic components  Ideal for thin films  Suitable for remote monitoring

recommended reading A. Blythe and D. Bloor; “Electrical Properties of Polymers”, Cambridge University Press, Cambridge (2005) D. Q. M. Craig; “Dielectric Analysis of Pharmaceutical Systems”, Taylor and Francis, London (1995) P. Hedvig; “Dielectric spectroscopy of polymers” Wiley, New York (1977) N. G. McCrum, B. E. Read and G. Williams; “Anelastic and Dielectric Effects in Polymeric Solids”, Dover, New York (1991) D. M. Price, “Thermomechanical and Thermoelectrical Methods”, in P.J. Haines (ed.) “Principles of Thermal Analysis & Calorimetry”, Royal Society of Chemistry, Cambridge (2002) J. P. Runt and J. J. Fitzgerald, ed., “Dielectric Spectroscopy of Polymeric Materials: Fundamentals and Applications”, American Chemical Society, Washington DC (1997)