Determining the contribution of epidermal cell shape to petal wettability using isogenic Antirrhinum lines.

The petal epidermis acts not only as a barrier to the outside world but also as a point of interaction between the flower and potential pollinators. The presence of conical petal epidermal cells has previously been shown to influence the attractiveness of the flower to pollinating insects. Using Antirrhinum isogenic lines differing only in the presence of a single epidermal structure, conical cells, we were able to investigate how the structure of the epidermis influences petal wettability by measuring the surface contact angle of water drops. Conical cells have a significant impact on how water is retained on the flower surface, which may have indirect consequences for pollinator behaviour. We discuss how the petal epidermis is a highly multifunctional one and how a battery of methods, including the use of isogenic lines, is required to untangle the impacts of specific epidermal properties in an ecological context.

Metastable underwater superhydrophobicity.

Superhydrophobicity is generally considered to be a thermodynamically stable wetting state. The stability of the plastron (the thin air film separating the substrate from the water in the superhydrophobic state) was studied in underwater experiments. The plastron exhibited a rapid decay after a well defined onset time, which was found to be dependent on the immersion depth. The plastron decay is explained in terms of a model, which is based on confocal microscopy measurements. The limited underwater plastron stability explains the rarity of permanently submerged superhydrophobic surfaces in nature and limits their scope for commercial applications.

Polyelectrolyte brush amplified electroactuation of microcantilevers.

This paper describes the electroactuation of microcantilevers coated on one side with cationic polyelectrolyte brushes. We observed very strong cantilever deflection by alternating the potential on the cantilever between +0.5 and -0.5 V at frequencies up to 0.25 Hz. The actuation resulted from significant increases in the expansive stresses in the polymer brush layer at both negative and positive potentials. However, the deflection at negative bias was significantly larger. We have developed a theoretical framework that correlates conformational changes of the polymer chains in the brush layer with the reorganization of ions due to the potential bias. The model predicts a strong increase in the polymer volume fraction, close to the interface, which results in large expansive stresses that bend the cantilever at negative potentials. The model also predicts that the actuation responds much stronger to negative potentials than positive potentials, as observed in the experiments.