Blahoslav Sedláček

Relaxation fluctuations in poly(2-hydroxyethyl methacrylate) gels swollen in butanol

SummaryQuasielastic light scattering measurements on transparent poly (2-hydroxyethyl methacrylate) (PHEMA) gels were performed under temperature equilibrium conditions at several temperatures from 40 to 80°C. All observed correlation functions departed from the single exponential decay with a long-time limit. The asymptotic value relaxation frequency Γa decreased steeply with decreasing temperature. The observed temperature dependence of Γa is interpreted as resulting from polymer fluctuations near the glass transition of weakly swollen PHEMA gels.

In-plane displacement measurements by means of image speckle analysis

Abstract The speckle photography method (single-beam speckle interferometry) was used to study the deformation of a high-density polyethylene film by determining the detail field of displacements in an enlarged image of the sample. The method is based on the analysis of changes in speckle patterns corresponding to two different deformation states, as the changes in the speckle patterns contain information about the change of the object. The displacement vector and Poisson ratio have been determined with an accuracy of 10% in the small deformation range (displacements of several microns). Limitations of the method, such as the range of measurable displacements, effect of image defocusing, and tilt of the sample, are discussed. Among advantages of the method are comparative simplicity (it does not require grating on the object surface) and the possibility of its application to larger deformations while maintaining the small deformation steps between two deformation states.

Behaviour of a turbid swollen gel during continuous heating, equilibration and cooling

SummaryUsing the integral and differential turbidity ratio methods, processes occurring during the continuous heating, equilibration and cooling of the Phema gel have been characterized. Microseparated particles were shown to be responsible for the turbidity changes below 40°C, even if not exclusively. The role of large scatterers called fluctuation microregions in the individual periods has been discussed.