Role of internal viscosity in polymer viscoelasticity

A microscopic insight into the deformation behavior of semicrystalline polymers: the role of phase transitions

The deformation behavior of semicrystalline polymers associated with polymorphic transformations under tensile deformation is discussed in the case of syndiotactic polypropylene. We report a phase diagram of this polymer where the regions of stability of the different polymorphic forms are defined as a function of the degree of stereoregularity and deformation. The values of critical strain corresponding to the structural transformations depend on the stereoregularity that affects the relative stability of the involved polymorphic forms and the state of the entangled amorphous phase.

Contact mechanics studies with the quartz crystal microbalance: origins of the contrast factor for polymer gels and solutions

A contact mechanics methodology utilizing the quartz crystal microbalance (QCM) has been applied to study the spreading behavior of polymer solutions and gels. Changes in the resonant frequency and in the dissipation are monitored as these materials are brought into contact with the electrode surface of the QCM. The primary application is in studies of elastic polymer gels, where spreading over the surface of the QCM is limited by the elasticity of the gel. Simultaneous measurement of the applied loads and displacements, along with measurement of the QCM/gel contact area, the frequency shift, and the dissipation, enable us to calibrate the QCM as a contact sensor. While changes in the frequency and dissipation both depend linearly on the contact area, measurements of the dissipation provide a more reliable indicator. The relationship between the dissipation and the contact area is determined by the solvent viscosity and by the high-frequency intrinsic viscosity of the system of interest. This result is consistent with previous results on the high-frequency rheological behavior of polymer solutions.

Some Applications of Fluorimetry to Synthetic Polymer Studies

Fluorimetry, a powerful research tool in the study of biological macromolecules, has a number of valuable applications in investigations of synthetic polymers. These techniques reveal the microscopically heterogeneous distribution of species in polymer systems, which is specially pronounced in solutions of polyelectrolytes. They also allow us to study conformational mobility of flexible chains, diffusion-controlled intermolecular reactions of macromolecular reagents, glass transition phenomena, and polymer compatibility.