A novel technique to measure the Poisson’s ratio and submicron lateral dimensional changes of ultrathin polymeric films

A sensitive technique for measurement of lateral dimension of the ultrathin polymeric films is developed. By comparing width profiles at various loads, the lateral and longitudinal strains were obtained, and were used to get the Poisson’s ratio. Lateral dimensional changes at a very light load and a range of temperatures and relative humidities were used to measure coefficients of thermal and hygroscopic expansion. The Poisson’s ratio of standard polyethelene terephthalate (PET), tensilized PET, standard polyethelene terephthalate (PEN), tensilized PEN and supertensilized PEN were measured at 25 °C/15%RH, 25 °C/50%RH, 25 °C/80%RH, and 40 °C/50%RH. The data range from 0.29 to 0.47. It is found that tensilized films have a higher Poisson’s ratio than balanced films. The effects of temperature and humidity on the Poisson’s ratio are related to the materials’ molecular structure. An increase in temperature generally increases the Poisson’s ratio for the polymeric films. When relative humidity increases, the Poisson’s ratio of balanced films increases, while those of tensilized films remains constant or decreases slightly. The Poisson’s ratio is also affected by the stress magnitude that is used in the measurement; high stress usually results in a high Poisson’s ratio. By simultaneous loading and calibration, long term lateral dimensional deformation behavior of these films was studied. The results are consistent with the reported data measured by standard techniques.