(748d) Novel Apparatus for Creep Measurements of Solvent Loaded Polymer Films

In the field of physical properties of polymeric films, creep measurements are essential to estimate the time-dependent increase in deformation under constant stress, thus providing information about the viscoelastic behavior of polymers (e.g. viscosity and elasticity modulus) [1]. During the last decades a lot of work has been conducted on creep measurements in solvent free systems, characterizing these mechanical parameters as a function of temperature [1-3]. However, it is well known that also dissolved substances (solvents) alter the mechanical properties of polymers [4]. Apart from tensile strength, these parameters remarkably influence diffusion processes within the polymer, especially, if the sorption or diffusion takes place below the glass transition of the polymer. However, to our knowledge there are no data available that allow studying the influence of solvent concentration on the mechanical properties of polymer films. Although several commercially apparatuses for creep-measurements are available, none of these is capable to measure the mechanical properties of the polymeric film under different solvent loadings and temperatures.

For that reason we developed and built a novel experimental setup combining the simplicity of a creep experiment with the complexity of the sorption process, especially for measurements at low pressures and in glassy polymers. This enabled us for the first time, to measure the increasing strain under constant stress at constant temperature and constant solvent loading. By comparing creep experiments of different solvent loaded polymer films with creep experiments of unloaded polymer films at different temperatures, we were able to directly analyze the effect of the solvent on the creep behavior as well as on the glass transition of the system.

[1] J. D. Ferry, Viscoelastic Properties of Polymers. New York: John Wiley & Sons Inc., 1980. [2] M. L. Williams, "Structural Analysis of Viscoelastic Materials," Aiaa Journal, vol. 2, pp. 785-808, 1964. [3] F. R. Schwarzl and L. C. E. Struik, "Analysis of Relaxation Measurements," Advances in Molecular Relaxation Processes, vol. 1, pp. 201-255, 1968. [4] M. L. Williams, R. F. Landel, and J. D. Ferry, "Temperature Dependence of Relaxation Mechanisms in Amorphous Polymers and Other Glass-Forming Liquids," Physical Review, vol. 98, pp. 1549-1549, 1955.