Force/displacement-temperature experiments

Force/Displacement-Temperature Experiments. Force as a function of temperature was obtained by placing a sample in a vertical glass oven and gripping both ends, with one end attached to a load cell and the other to an adjustable mount. A slow nitrogen flow was introduced through the bottom and an RTD probe was placed near the middle of the sample. Output from the probe and load cell was recorded on a Bascom-Turner Instrument model 4000. With a sample in place several heating and cooling cycles were performed at various loads. 

The linear dependence on ks is a strong advantage compared to the force-modulation SFM. Due to the inertia of the cantilever mass at high frequencies, the tip cannot follow completely the displacement of the sample. This results in smaller elastic deformations and low forces in the pN range, which are measured by accelerated mass md2zldt2. Recently, the SLAM technique has been advanced toward variable temperature experiments [138]. Before this development, temperature ramps have been used to perform local calorimetry [139]. 

Relevant and complementary information about the damage process of polymers can be obtained among others by the analysis of the force-displacement curves, by the observation of the fracture surfaces (cf. Sects. 3.2.5 and 5.4) and, as will be shown in Sect. 6.2.2, by the determination of the amount of voids in a sample during and/or after deformation. However, a complete elucidation of the deformation mechanisms is only possible by their direct observation at the sub-micron level. Transmission electron microscopy is often used for this purpose. For convenience, the tests (which require experience and touch) are generally carried out at room temperature and at a low strain rate. 

The target temperatures were the same as in the shear and tensile experiments. Three specimens were tested at each temperature (designated Cxx, with xx being the temperature). After the target temperature was reached, the axial compressive force was applied with a displacement rate of 1 mm min until specimen failure. 

Electronic polarization a can be observed in all dielectrics irrespective of whether other types of polarization are displayed in the dielectric. Electronic polarization is the displacement of electrons with respects to the atomic nuclens, to be more precise—the displacement of the orbits imder the action of an external electric field. When the system is subjected to an external field of intensity E, the nucleus and the electron experience Lorentz forces in opposite directions. When atoms form molecules, electronic polarization is still possible, but there may be additional polarization due to a relative displacement of the atomic components of the molecule in the presence of an electric field. When a field is applied to the molecule, the atoms in the molecule are displaced in opposite directions imtil ionic binding force stops the process and ionic polarization a arises, thus increasing the dipole moment. It is found that electronic and ionic polarizations are functions of molecular stracture and are largely independent of temperature. 

---