Nano-structured Soft Materials 1
Exercise XI
To be discussed on 12.01.2016
Problem 1
The Dielectric Relaxation Spectroscopy is a powerful technique to investigate the dynamics of
the polymers. It measures the dielectric permittivity (ε*) of the sample as a function of the
applied frequency. Can you explain why it is possible to observe the glass transition of the
polymer in the dielectric permittivity data? How it is called the dynamic process associated to
the glass transition of the polymer? For which kind of polymers do you expect to observe the
so-called “secondary” relaxation processes (so-called β or γ-process)?
Problem 2
The Vogel-Fulcher-Tammann-Hesse (VFTH) equation is much used to extrapolate the glass
transition value Tg of glass forming substances from viscosity measurements. From Dielectric
Spectroscopy measurements it is also possible to calculate the Tg of the glass former. Indeed,
the relaxation time of the cooperative motion of the glass former follows the VFTH behavior:
𝜏 = 𝜏0 𝑒 𝐵⁄(𝑇−𝑇0 )
From the VFTH fit of the DRS data of a partially amorphous PEO sample, the flowing fitting
parameters were obtained: τ0=7.14 x 10-8 s, B=581 and T0=174.5 K. Calculate the glass transition
of the PEO sample, assuming that τ(Tg)=100 s.
Problem 3
The dielectric relaxation spectroscopy measurements of a partially amorphous PU-PEO diblock
polymer (Tg=-78°C) sample give the following spectra respectively at a) T<-80°C b) T>-80°C. How
would you assign the relaxation processes occurring in the sample? Note that each relaxation
process appears as a maximum in the permittivity data.