Measuring the low frequency linear viscoelastic properties of polymer melts: Trials with PDMS using sphere-plane squeeze flow and interferometry

The problem of measuring the linear viscoelastic (LVE) properties of polymers at low frequencies is a longstanding one, especially for polyolefins with broad relaxation times and small time-temperature shift factors. A squeeze flow apparatus utilizing Newton's interference rings has been devised to measure minute strains at very low stresses with a minimum resolution of (1)/(4) wavelength of light. Its simplicity allows several samples to be run simultaneously under vacuum. This arrangment minimizes degradation, manhours and cost, all critical considerations for long experiments. The design and preliminary results for PDMS as measured by a prototype of the instrument will be discussed.