A study on water absorption in freestanding polyurethane films filled with nano-TiO2 pigments by capacitance measurements

The electrochemical impedance spectroscopy (EIS) was used to evaluate the water transport and dielectric properties of polyurethane films filled with nano-TiO2 at different pigment/base (P/B) values in 0.5 mol/L NaCl solutions. EIS results were compared with gravimetric measurements on the freestanding films. The amount of water absorption showed great discrepancy between the two methods. The diffusion coefficient in the polyurethane film with P/B=30% was the smallest among those filled with nano-TiO2 pigments. The dielectric constant ɛ of the polyurethane varnish film obtained from the initial capacitance was in the range of typical values of polymers. SEM was used to measure the distribution of nano-TiO2 particles in the polyurethane films.