Page 41 - Handbook of Thermal Analysis of Construction Materials

Section 3.0 - Modern Techniques 25

Dielectric analysis (DEA) may be used for characterizing high
performance thermoplastics such as poly(ether ether ketone) (PEEK), [63]
which is used as a matrix in advance composites. It may also be used for
monitoring the plasticizing effects of moisture on polymer transi-
tions, [60] electronics, pharmaceutical, [64] petrochemical, and food prod-
ucts. [65] Despite the wide range of applications, no work has been
reported in the literature on the use of DEA in the characterization of
construction materials. The technique may have potential in the new field
of conductive concrete recently developed by Xie, et al. [66] DEA could
also be used to monitor the curing of construction adhesives and
sealants.
One of the advantages of DEA application over conventional
thermoanalytical techniques is that it has the ability to handle highly brittle
and very soft samples. For example, DMA measurements require mechani-
cal deformation of the sample when measuring the viscoelastic properties
of the material. If the material is too brittle, it will crack during deformation.
On the other hand, characterization of very soft materials requires support,
and, in some cases, cannot be characterized with some DMA instruments.
However, DEA can overcome these difficulties since it requires neither
clamping nor mechanical deformation. Hence, DEA can yield excellent
material data on both brittle and soft samples, including tar and waxes. It is
quite difficult to analyze these materials by DMA because they become
very brittle below their glass transition temperature and very soft when
heated above the melting point. The difficulty in using DEA though is that
good contact with the sample is needed, which is not always easy with hard
samples.
In addition, DEA is effective for rheological studies because by
monitoring the movement of ions in a single test, it can identify key events

affecting rheological changessuch as time or temperature corresponding to
the minimum viscosity, the onset of the flow, the onset of cure and its
completion, the maximum rate of reaction and transition to a glassy
phase. [67] The technique has a higher sensitivity than DSC for analyzing the
stages of cure as well as good stability for liquid evaluation.
As can be seen, DEA has much potential. It helps scientists and
technology in achieving a new understanding of the structure and behavior
of materials. [64] It is anticipated that this technique will be widely used in
construction within the next ten years.