Poly­(dimethylsiloxane) (PDMS)- and poly­(ethylene oxide) (PEO)-based block copolymer coatings functionalized with amphiphilic, surface-active, and sequence-controlled oligomer side chains were studied to directly compare the effects of hydrophilicity, hydrogen bonding, and monomer sequence on antifouling performance. Utilizing a modular coating architecture, structurally similar copolymers were used to make direct and meaningful comparisons. Amphiphilic character was imparted with non-natural oligopeptide and oligopeptoid pendant chains made from oligo-PEO and surface-segregating fluoroalkyl monomer units. Surface analysis revealed rearrangement for all surfaces when moved from vacuum to wet environments. X-ray photoelectron spectroscopy (XPS) spectra indicated that the polymer backbone and oligomer interactions play key roles in the surface presentation. Biofouling assays using the macroalga Ulva linza showed that the presence of peptoid side chains facilitated the removal of sporelings from the PDMS block copolymer, with removal matching that of a PDMS elastomer standard. The lack of a hydrogen bond donor in the peptoid backbone likely contributed to the lower adhesion strength of sporelings to these surfaces. Both the initial attachment and adhesion strength of the diatom Navicula incerta were lower on the coatings based on PEO than on those based on PDMS. On the PEO coating bearing the blocky peptoid sequence, initial attachment of N. incerta showed no measurable cell density.

The influence of zwitterionic self-assembled monolayers on settlement and removal of algae was studied. The monolayers were constructed either from zwitterionic thiols or from solutions of positively and negatively charged thiols. The cationic component was composed of quaternary ammonium terminated thiols and the anionic component contained sulfate or carboxylate termination. During assembly, all surfaces showed a strong tendency for equilibration of the surface charge. Settlement and adhesion assays with zoospores of Ulva linza and the diatom Navicula incerta, and field tests of the initial surface colonization revealed the relevance of charge equilibration for the biological inertness of the prepared surfaces.

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The effect of incorporation of silicone oils into a siloxane-polyurethane fouling-release coatings system was explored. Incorporation of phenylmethyl silicone oil has been shown to improve the fouling-release performance of silicone-based fouling-release coatings through increased interfacial slippage. The extent of improvement is highly dependent upon the type and composition of silicone oil used. The siloxane-polyurethane (SiPU) coating system is a tough fouling-release solution, which combines the mechanical durability of polyurethane while maintaining comparable fouling-release performance with regard to commercial standards. To further improve the fouling-release performance of the siloxane-PU coating system, the use of phenylmethyl silicones oils was studied. Coatings formulations were prepared incorporating phenylmethyl silicone oils having a range of compositions and viscosities. Contact angle and surface energy measurements were conducted to evaluate the surface wettability of the coatings. X-ray photoelectron spectroscopy (XPS) depth profiling experiments demonstrated self-stratification of silicone oil along with siloxane to the coating-air interface. Several coating formulations displayed improved or comparable fouling-release performance to commercial standards during laboratory biological assay tests for microalgae (Navicula incerta), macroalgae (Ulva linza), adult barnacles (Balanus amphitrite syn. Amphibalanus amphitrite), and mussels (Geukensia demissa). Selected silicone-oil-modified siloxane-PU coatings also demonstrated comparable fouling-release performance in field immersion trials. In general, modifying the siloxane-PU fouling-release coatings with a small amount (1-5 wt % basis) of phenylmethyl silicone oil resulted in improved performance in several laboratory biological assays and in long-term field immersion assessments.

Food system resilience has multiple dimensions. We draw on food system and resilience concepts and review resilience framings of different communities. We present four questions to frame food system resilience (Resilience of what? Resilience to what? Resilience from whose perspective? Resilience for how long?) and three approaches to enhancing resilience (robustness, recovery, and reorientation—the three “Rs”). We focus on enhancing resilience of food system outcomes and argue this will require food system actors adapting their activities, noting that activities do not change spontaneously but in response to a change in drivers: an opportunity or a threat. However, operationalizing resilience enhancement involves normative choices and will result in decisions having to be negotiated about trade-offs among food system outcomes for different stakeholders. New approaches to including different food system actors’ perceptions and goals are needed to build food systems that are better positioned to address challenges of the future. Expected final online publication date for the Annual Review of Environment and Resources, Volume 47 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.