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Polymer Materials and Engineering
print
Dlelectric Spectroscopy
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Dr. M. Wübbenhorst | |||||||||
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Research
Dielectric Relaxation Spectroscopy
Dielectric relaxation spectroscopy (DRS) reveals the molecular dynamics of polymeric materials by the characteristic response of polar groups and ions to a time-dependent electrical field. The extremely wide range in relaxation times is related to typical length scales associated to specific motions (local bond rotations, segmental motions, relaxation of the entire chain).Nowadays, highly automated spectrometer allow fast and accurate dielectric measurements in a wide frequency range (10-3 - 109 Hz) and at temperature usually ranging from -160° - 400°C.
In our department, dielectric spectroscopy is mainly used for the characterization of dynamic processes present in polymers and polymer-based materials. Their dynamics involve many (hierarchical) relaxation processes ranging from simple local bond-rotations, larger segmental motions up to relaxations of the entire polymer chain (Rouse or reptation dynamics). Such processes can be studied in the liquid and solid state making DRS a powerful tool also for the study of both kinetic processes and thermodynamic transitions.
Thermal wave techniques
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When a solid is exposed to a periodical, time-dependend heat flow (e.g.
provided by an intensity modulated laser), a time- and position dependent
temperature profile T(x,y,z,t) is generated, which can formally described
as thermal wave. Since the actual temperature distribution T(x,y,z,t) is
the result of both the generation (e.g. by light absorption) and
propagation of heat (by thermal diffusion), the direct measurement
of the temperature profile allows the determination of thermal or optical
properties of the sample. Furthermore, the interaction of the thermal waves with
temperature dependent physical properties like density, dielectric constant or
electrical polarization allows the spatially resolved study of these and
many solid-state properties.
Polymer electrets and other pyroelectric materials
In our group, piezo- and pyroelectric materials have been a topic of interest for many year. Besides "classical" polymer electret materials like poly(vinylidene fluoride) (PVDF) and various charge electrete materials (PP, Teflon-FEP, PTFE), recent research is focused on novel porous polymer electrets, which exhibit outstanding charge storage properties. For the study of the thermal stability and the spatial distribution of the pyroelectric and piezoelectric properties, several experimental techniques are available:- thermally stimulated discharge measurements (TSD),
- thermal wave techniques (LIMM) for the measurement of pyroelectric distributions,
- the piezoelectrically generated pressure step technique (PPS) for high resolution acoustic profiling of charge and polarisation distributions,
- scanning pyroelectric microscopy (SPEM) for 3-dimensional scanning of pyroelectric properties.
In extension to polymer electrets, we are further interested in novel piezo- and pyroelectric host-guest materials, which are based on zeolites (Prof. J.C. Jansen, DCT) and organic inclusion compounds (Prof. J. Hulliger, Univ. of Berne).
Projects
Dielectric Relaxation Spectroscopy
- Dynamics of ultra-thin polymer films
- Dynamics of liquid crystals (LC) and LC polymers (LCPs)
- Eectrical properties of (Li+) ion-conducting polymers (polymer electrolytes)
- Glass transition dynamics in confined geometries
- Real-time monitoring of chemical (curing) and physical (crystallisation) structure evolution by DRS
- Hierarchic dynamics in supramolecular polymers
- Porous thin polymer films as ultra-low-k dielectrics
Thermal wave techniques
- Pyroelectric calorimetry for the measurement of thermal conductivity, specific heat and thermal effusivity in solids
- Space charge and polarisation distributions studied by the Laser intensity modulation method (LIMM)
- Imaging of pyroelectric properties by scanning pyroelectric microscopy (SPEM)
- Imaging of thermal properties by scanning pyroelectric microscopy (SPEM)
Polymer electrets and other pyroelectric materials
- Poling behaviour, pyro- en piezoelectric behaviour of (porous) polymer electrets (Prof. J. van Turnhout)
- Polarity formation and dynamics in zeolite based nanoporous host-guest materials
- Polar domain order in organic inclusion compounds containing NLO-active dipolar guest molecules (Prof. J. Hulliger, University Berne)
Links
| Polymer Materials | Prof. dr. S.J. Picken |
| Polymer Engineering | Prof. dr. S.J. Picken |
| Polymer Physics | Prof. dr. ir. J. van Turnhout |
| Polymer Synthesis | Dr. W.F. Jager |
| Towards New "Soft" Polymer Systems | Dr. Eduardo Mendes |
| PME home |
Contact
Faculty of Applied Sciences
Julianalaan 136
2628 BL Delft
The Netherlands
Tel. : +31(0)15 278 18 28
Secretariat-PME@tnw.tudelft.nl
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