Alginate readily aggregates and forms a physical gel in the presence of cations. The association of the chains, and ultimately gel structure and mechanics, depends not only on ion type, but also on the sequence and composition of the alginate chain that ultimately determines its stiffness. Chain flexibility is generally believed to decrease with guluronic residue content, but it is also known that both polymannuronate and polyguluronate blocks are stiffer than heteropolymeric blocks. In this work, we use atomistic molecular dynamics simulation to primarily explore the association and aggregate structure of different alginate chains under various Ca(2+) concentrations and for different alginate chain composition. We show that Ca(2+) ions in general facilitate chain aggregation and gelation. However, aggregation is predominantly affected by alginate monomer composition, which is found to correlate with chain stiffness under certain solution conditions. In general, greater fractions of mannuronic monomers are found to increase chain flexibility of heteropolymer chains. Furthermore, differences in chain guluronic acid content are shown to lead to different interchain association mechanisms, such as lateral association, zipper mechanism, and entanglement, where the mannuronic residues are shown to operate as an elasticity moderator and therefore promote chain association.

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A general model for interfacial polymerization is proposed and solved numerically. The model takes into account diffusion and reaction of monomers, presence of unreacted functional groups on the growing polymer, and solubility effects. The formation of a polyamide film in composite separation membranes is taken as an example. The evolution of the concentrations of the polymer and unreacted moieties are followed explicitly, thus enabling the calculations of the limiting thickness and the asymmetric distribution of density and charge in the resulting film. Such knowledge is important for the prediction of rejection and transport properties of the film. The effects of reaction kinetics, monomer concentrations, and hydrodynamic conditions on the properties of the film are analyzed, and a number of analytical correlations are developed.

Integrating self-healing capabilities into soft electronic devices increases their durability and long-term reliability. Although some advances have been made, the use of self-healing electronics in wet and/or (under)water environments has proven to be quite challenging, and has not yet been fully realized. Herein, a new highly water insensitive self-healing elastomer with high stretchability and mechanical strength that can reach 1100% and ≈6.5 MPa, respectively, is reported. The elastomer exhibits a high (>80%) self-healing efficiency (after ≈ 24 h) in high humidity and/or different (under)water conditions without the assistance of an external physical and/or chemical triggers. Soft electronic devices made from this elastomer are shown to be highly robust and able to recover their electrical properties after damages in both ambient and aqueous conditions. Moreover, once operated in extreme wet or underwater conditions (e.g., salty sea water), the self-healing capability leads to the elimination of significant electrical leakage that would be caused by structural damages. This highly efficient self-healing elastomer can help extend the use of soft electronics outside of the laboratory and allow a wide variety of wet and submarine applications.

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