Most of the aerial organs of vascular plants are covered by a protective layer known as cuticle. The main purpose of this nanocomposite membrane is to limit the plant’s transpirational water loss. Cuticles display a compositionally graded structure consisting of three main components: a matrix made from the cross-linked polyester cutin, hydrophilic polysaccharides that extend from the underlying cell walls and become less prominent towards the outside, and hydrophobic waxes that dominate the surface. Expecting that membranes with such a polarity gradient would display asymmetric water transport, we prepared nanocomposite membranes consisting of hydrophilic cellulose nanocrystals (CNCs) and a hydrophobic SBS copolymer matrix. We exploited the colloidal instability of CNCs and their propensity to sediment during a solvent casting process to create compositionally graded membranes, in which the CNC content varies along the transversal direction. The structure and composition of these membranes could be easily varied and this enabled a systematic investigation. The water permeation is indeed directional, with asymmetry factors of up to 2.5. We also investigated the water transport through olive and ivy leaf cuticles. The water transport through these biomembranes is also directional, but the direction of preferred transport is against the polarity gradient. We show that this behavior roots in the fact that the permeability of these membranes is regulated by the hydration of the cutin-rich layer.

Asymmetric water transport in dense leaf cuticles and cuticle-inspired compositionally graded membranes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.