Research on the measurement of hygroscopic properties and prediction of deformation for flexible polymer substrates

Abstract

The prediction of hygroscopic deformation for flexible polymer substrates is crucial in various fields from smart structures to flexible electronics. In this study, the prediction method of hygroscopic deformation is presented by employing the transient finite element method (FEM) model. In order to consider the strain gradients inside the substrate precisely, the time-dependent characteristic of moisture distribution is quantitatively investigated by coupling the moisture absorption process with mechanical deformation analysis. The essential hygroscopic properties including the saturated moisture content, moisture diffusivity, and coefficient of moisture expansion are precisely measured. Through the application of these hygroscopic properties to the FEM model, the moisture distribution and hygroscopic deformation are quantitatively simulated with time. For the verification of this FEM model, the simulation results of bilayer structure are compared with the experimental results, which are measured by the three-dimensional deformation measurement system. The presented model demonstrates that the global and local hygroscopic deformation are accurately predicted by this approach, showing above 90% averaged accuracy at each time step. Based on the presented prediction model, the hygroscopic deformation for the multilayered and patterned structure is also accurately predicted. Finally, parameter study using FEM approach is performed for the exposed area to the moisture in order to analyze the effect of patterns on the hygroscopic deformation behavior. This study indicates that the magnitude and local deformation profile can be efficiently controlled through the presented FEM approach and the measurement technique for the hygroscopic properties.