PSMG
 EUSMI
 Instruments
 Detecting molecular motions
The Dielectric Spectroscopy Laboratory

Announcement:


INTRODUCTION
The dielectric spectroscopy laboratory is a general purpose facility which is focused and optimized for the study of dynamical processes in polymers in particular and other soft-matter in general (see below).

External users can get support for free access to this infraestructure in the framework of EUSMI (European infrastructure for spectroscopy, scattering and imaging of soft matter)

The main features of the laboratory are:
- It covers a huge dynamical range, allowing the investigation of dynamical processes over more than 16 orders of magnitude in the time/frequency scale.
- Several non-conventional sample environments are available over limited frequency ranges. For example, the measurement temperatures can be extended down to as low as 10K. Moreover, high-pressure measurements are possible up to 300 MPa.
- Recently, nanometer scale laterally resolved dielectric spectroscopy has become possible by using standard AFM equipments in combination with a dedicated lock-in amplifier.

To access all these capabilities several instruments are combined (see scheme below).




INSTRUMENTS AT THE DIELECTRIC SPECTROSCOPY LABORATORY

Although most of the instruments in the laboratory work on the frequency domain, time domain techniques are used to access the very slow dielectric relaxation processes. In the former case, the frequency dependent impedance of a capacitor formed with the sample is usually determined. Contrary, what is measured in the time domain techniques is the subsequent current associated to the depolarization process of a specimen previously subjected to a pulse shape excitation. Nevertheless, a direct comparison of the results obtained is not difficult. (see below)

Most of the equipments are provided by the same supplier (Novocontrol) facilitating the experiments for occasional users. The Manuals are accessible from onsite computers.

FREQUENCY DOMAIN INSTRUMENTS

-Broad-Band Dielectric Spectrometers (BBDS): ALPHA-A Novocontrol
Frequency range: 1e-5 - 3e7 Hz (sensitivity better than tand ~1e-4)
Temperature range: 100 - 600 K (stability better than 0.01 K)

-High-Frequency Dielectric Spectrometer (HFDS): Agilent E4991A RF-Impedance Analyzer
Frequency range: 1e6 - 3e9 Hz (sensitivity better than tand ~1e-3)
Temperature range: 100 - 600 K (stability better than 0.01 K)

-Micro-Wave Dielectric Spectrometer (MWDS): Agilent E8361A Microwave Network Analyzer
Frequency range: 2e7 - 5e10 Hz (sensitivity better than tand ~1e-1)
Temperature range: 200 - 500 K (stability better than 0.01 K)

-Therahertz Spectrometer (THS): Teraview 3000 spectrometer
Frequency range: 5e10 - 4e12 Hz (sensitivity better than tand ~1e-1)
Temperature range: 250 - 520 K (stability better than 0.1 K)

-High-Pressure Dielectric Spectrometer (HPDS): Concept 100 Novocontrol
Frequency range: 1e-2 - 1e6 Hz (sensitivity better than tand ~1e-4)
Pressure range: 0 - 300 MPa (stability better than 0.1 MPa)
Temperature range: 270 - 520 K (stability better than 0.1 K)

-Low-Temperature Dielectric spectrometer (LTDS): ALPHA-A Novocontrol
Frequency range: 1e-2 - 1e6 Hz (sensitivity better than tand ~1e-4)
Temperature range: 10 - 320 K (stability better than 0.1 K)

TIME DOMAIN INSTRUMENTS

-Time-Domain Dielectric Spectrometer (TDDS): Novocontrol
Time range: 1 - 1e6 s (current sensitivity better than ~1e-16A)
Temperature range: 100 - 600 K (stability better than 0.01 K)

-Thermally Stimulated Depolarization Currents (TSDC): Novocontrol
Heating rate range: 0.1 - 10 K min-1 (current sensitivity better than ~1e-16A)
Temperature range: 100 - 600 K (accuracy better than 0.1 K)

LOCAL AFM-BASED DIELECTRIC RELAXATION

-nano-Dielectric Spectroscopy (nDS): AFM MultiMode V (Brucker) + SRS lock-in amplifier
Lateral resolution ~20 nm
Frequency range: 1 - 1e6 Hz (sensitivity better than tand ~1e-1)
Temperature range: 260 - 450 K (stability better than 1 K)


Schematic view of the dielectric laboratory equipments

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DIELECTRIC SPECTROSCOPY AND MOLECULAR MOTIONS

The dielectric spectroscopy consists in the study of the frequency dependent complex dielectric permittivity of insulator materials. The frequency range more commonly investigated is below a few GHz where the dielectric response of the insulator materials is usually dominated by orientational polarization processes. If the material under investigation contains permanent dipoles with a molecular origin, the dielectric spectroscopy would allow to get insight about the molecular motions.

A schematic diagram of the application of dielectric spectroscopy to the investigation of molecular motions is shown below. In the simplest case, the sample is a part of a parallel plate capacitor. In such a case the frequency dependent complex dielectric permittivity is proportional to the specimen complex capacitance, which can be measured with great accuracy over an extremely wide frequency range. For an alternating voltage of very high frequency the dipoles would not be able to follow the electric field direction and the measured dielectric permittivity will be essentially determined by the induced atomic and electronic material polarization. As the frequency is continuously reduced the molecular dipoles try to orient in the field direction. The level of orientation increases as the frequency is reduced and consequently the dielectric permittivity increases. At sufficiently low frequencies the molecular dipoles would be able to follow the field direction and a plateau value of the dielectric permittivity would result. In the frequency range where the dielectric permittivity increases, dispersion range, there is and associated energy dissipation process which manifests as a peak of the imaginary part of the complex dielectric permittivity. The reciprocal of the angular frequency of the dielectric loss peak provides a direct measure of the characteristic time of the molecular motions responsible of the dipolar orientation.

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Laboratory
Course
Notes

onsite only
 
Fundamentals of electrostatics and dielectric materials 
Polarization and dielectric permittivity 
Dielectric relaxation 
Phenomenological models of dielectric relaxation 
Experimental methods 
Introduction to data analysis 
Sample preparation procedures

Contact |Where we are | Last updated December 2017