Competing with barnacle cement: wetting resistance of a re-entrant surface reduces underwater adhesion of barnacles

Abstract

Surfaces with re-entrant topographies can repel liquids even of extremely low surface tension, almost independently of the material's inherent wettability. We show that this topography-based wetting resistance can also be applied to underwater applications, reducing the permanent adhesion of marine hardfouling organisms. Having combined a biofouling assay in the marine environment with microscopic analyses, we demonstrate how a synergistic effect of a soft silicone-based material with a re-entrant mushroom-shaped surface topography strongly increases the fouling release ability of such coatings compared with a smooth control made from the same material. Our coating inhibited the complete wetting of the solidifying glues produced by marine organisms, which resulted in a decreased contact area and, consequently, low adhesion. Our work suggests that topography-induced wetting resistance of surfaces may become a viable approach in preventing permanent adhesion of marine hardfouling organisms.

The Influence of Material and Roughness on the Settlement and the Adhesive Strength of the Barnacle Balanus Improvisus in the Baltic Sea

“…The samples were submerged in the Kiel Fjord (5419'46.200 N, 1010'28.400 E). They were mounted on PVC pipes in a perforated plastic barrel having holes with a diameter of 15 cm to protect them from predation, high currents and impact of flotsam ( Figure 1A; Petersen et al, 2018). If predation was observed during the field experiment the detached barnacles weren't considered during the fouling release evaluation.…”

“…If a barnacle had been detached from a surface, the duration of its settlement in weeks prior to the detachment was monitored. [For a more detailed description about the mussel presence during the experiment (see Petersen et al, 2018)]. Mussels were not considered during fouling evaluation.…”

“…The parameter "attachment duration" refers to the time interval between the initial attachment and the possible detachment of a barnacle from a surface. The parameter "release-to-settlement (r/s)" (Petersen et al, 2018) refers to the total number of released barnacles divided by the total number of settled ones and is used together with the attachment duration to quantitatively compare the fouling release ability between the different surfaces. Since epoxy resin samples show no fouling release ability, attachment duration and r/s were only evaluated for PVS samples.…”

“…Release-to-settlement ratios (r/s) according to Petersen et al (2018) were calculated by dividing the number of released barnacles by the total number of settled ones. Figure 6C displays the calculated r/s values for each roughness.…”

“…Due to the high temporal resolution during tracking of individual barnacles, new parameters describing the initial fouling settlement and fouling dynamics of the samples were identified. These include (1) initial settlement, (2) fouling dynamics, (3) actual barnacle density at the end of the experiment, (4) cumulative barnacle density (adding all detached barnacles to the ones still attached), (5) attachment duration prior to release and (6) release-to-settlement ratio (Petersen et al, 2018). With all these new parameters, our approach was to evaluate the influence of stiffness, SFE and roughness on adult barnacle adhesion to understand whether strong and reliable adhesion of adult barnacles is always directly associated with the substrate choice made at the cyprid larval stage (Aldred et al, 2010).…”