Directional water transport in laminated polymer

Directional transport of chemical species through compositionally graded dense membranes is of fundamental interest and relevant for applications such as separation processes and smart packaging. While theoretical models have elucidated the mechanism underlying directional mass transport in such materials, experimental studies are limited. Here, we explore the potential of dense bilayer membranes consisting of hydrophilic polyvinyl alcohol (PVA) and hydrophobic poly(styrene)- block -poly(butadiene)- block -poly(styrene) (SBS) to achieve directional water transport. In these laminates, which are mechanically stable and only delaminate under extreme conditions, the PVA layer swells and becomes plasticized upon exposure to moisture, leading to increased permeability when the membrane's PVA side faces a humid environment; this effect is absent when the SBS side is exposed to moisture. Optimized membrane architectures exhibit an asymmetry factor of up to 6. Complemented by modeling results, our systematic investigation provides valuable insights into directionality in mass transport through asymmetric membranes. • Dense bilayer membranes with directional transport properties remain underexplored. • Hydrophobic/hydrophilic laminates show direction-dependent water permeability. • Strong directionality arises from structural asymmetry and water plasticization. • Transport switches from symmetric to asymmetric behavior at high relative humidity. • Resistance-in-series model proves transport trends but lacks quantitative accuracy.