Experimental Techniques

Thermal properties

The heat capacity is a measure for the number of microscopic degrees of freedom. It is therefore sensitive to changes of structure or dynamics of polymers due to interactions with other materials. Besides this, calorimetry is a standard tool to study phase transitions in polymers, e.g. by measuring latent heats. The LPM currently exploits four different calorimeters which allow to measure complex specific heat capacities with sinusoidal or stochastic temperature modulation. Two of the calorimeters are modified to extend the available temperature range from -220°C (with He cooling) to +600°C.

 

Rheometer

Mechanical properties

The presence of filler particles in polymers and the formation of interphases in the polymers around the filler particles lead to changed flow behavior in the liquid phase. The same holds true for structure formation in polymers. Linear and non-linear flow behavior as well as viscoelastic properties are currently investigated at the LPM using two different viscosimeters/rheometers. In the solid phase, mechanical properties are studied using a DMA (Dynamic Mechanic Analysis) machine. The available frequency range spans from 1 mHz to 1 kHz.
(Picture: Rheometer/@ Michel Brumat)

 

Electrical properties

Polymers usually exhibit molecular dynamics on a very large scale. Interactions of polymer molecules with other materials take influence on these dynamics. The LPM uses a dielectric spectrometer to study the dielectric properties between 10-3 and 107 Hz. This gives also access to the DC conductivity which may be changed by interphases in the polymers. 
(Picture: Dielectric Spectrometer, Aleksander Ostrowski / @ Michel Brumat)

 

Hypersonic mechanical properties

Brillouin spectroscopy grants access to dynamic mechanical properties at GHz frequencies and thereby allows for the investigation of quasi-static properties of polymers even in the liquid as well as in the solid phase. Besides the advantages of being destructionless and contactless a further highlight is the ongoing development of Brillouin microscopy. Brillouin microscopy makes it possible to record spatial profiles of mechanical properties, e.g. as they occur in polymer interphases, and moreover even their temporal evolution.The achieved spatial resolution is about 1µm and the temporal resolution can be of the order of a few minutes.
(Picture: Brillouin spectroscopy, Ullrich Mueller /@Michel Brumat)

 

Refractometry

The refractive index is linked to mass density and electronic polarizability both being related to the molecular structure and to the molecular interaction. Because of its outstanding resolution of 10-6 state-of-the-art refractometry is therefore able to resolve subtle changes of these properties, e.g. due to changes of temperature, a chemical reaction or a phase transition. The capability to link optical properties to structural ones is fostered by introducting a sinusoidal modulation of temperature. This approach allows for a quasi-isothermal determination of a complex thermal expansion coefficient which bears information about structural relaxtions and the molecular interaction potential.

 

Structural properties

A deep understanding of structure-properties relationships is essential for the improvement of materials or the creation of materials with completely new properties. To investigate  features like the influence of interfaces on the structure of physical or chemical networks, dispersion of particles in multi-component systems or shear induced crystallization, the LPM is exploiting polarization microscopy and Atomic Force Microscopy (AFM).
(Picture: Polymer Microscope, Aleksander Ostrowski / @Michel Brumat)