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Covalent carbon–carbon bonds are hard to break. Their strength is evident in the hardness of diamonds and tensile strength of polymeric fibres; on the single-molecule level, it manifests itself in the need for forces of several nanonewtons to extend and mechanically rupture one bond. Such forces have been generated using extensional flow, ultrasonic irradiation, receding meniscus and by directly stretching a single molecule with nanoprobes. Here we show that simple adsorption of brush-like macromolecules with long side chains on a substrate can induce not only conformational deformations, but also spontaneous rupture of covalent bonds in the macromolecular backbone. We attribute this behaviour to the fact that the attractive interaction between the side chains and the substrate is maximized by the spreading of the side chains, which in turn induces tension along the polymer backbone. Provided the side-chain densities and substrate interaction are sufficiently high, the tension generated will be strong enough to rupture covalent carbon–carbon bonds. We expect similar adsorption-induced backbone scission to occur for all macromolecules with highly branched architectures, such as brushes and dendrimers. This behaviour needs to be considered when designing surface-targeted macromolecules of this type—either to avoid undesired degradation, or to ensure rupture at predetermined macromolecular sites. [ABSTRACT FROM AUTHOR]

Self-healing polymeric materialsare systems that after damagecan revert to their original state with full or partial recovery ofmechanical strength. Using scaling theory we study a simple modelof autonomic self-healing of unentangled polymer networks. In thismodel one of the two end monomers of each polymer chain is fixed inspace mimicking dangling chains attachment to a polymer network, whilethe sticky monomer at the other end of each chain can form pairwisereversible bond with the sticky end of another chain. We study thereaction kinetics of reversible bonds in this simple model and analyzethe different stages in the self-repair process. The formation ofbridges and the recovery of the material strength across the fracturedinterface during the healing period occur appreciably faster aftershorter waiting time, during which the fractured surfaces are keptapart. We observe the slowest formation of bridges for self-adhesionafter bringing into contact two bare surfaces with equilibrium (verylow) density of open stickers in comparison with self-healing. Theprimary role of anomalous diffusion in material self-repair for shortwaiting times is established, while at long waiting times the recoveryof bonds across fractured interface is due to hopping diffusion ofstickers between different bonded partners. Acceleration in bridgeformation for self-healing compared to self-adhesion is due to excessnonequilibrium concentration of open stickers. Full recovery of reversiblebonds across fractured interface (formation of bridges) occurs afterappreciably longer time than the equilibration time of the concentrationof reversible bonds in the bulk. [ABSTRACT FROM AUTHOR]

Mechanical activation of chemical bonds typically involves the application of external forces, which implies a broad distribution of bond tensions. We demonstrate that controlling the flow profile of a macromolecular fluid generates and delineates mechanical force concentration, enabling a hierarchical activation of chemical bonds on different length scales from the macroscopic to the molecular. Bond tension is spontaneously generated within brushlike macromolecules as they spread on a solid substrate. The molecular architecture creates an uneven distribution of tension in the covalent bonds, leading to spatially controlled bond scission. By controlling the flow rate and the gradient of the film pressure, one can sever the flowing macromolecules with high precision. Specific chemical bonds are activated within distinct macromolecules located in a defined area of a thin film. Furthermore, the flow-controlled loading rate enables quantitative analysis of the bond activation parameters. [ABSTRACT FROM AUTHOR]

Self-organization of nanoparticles is an efficient strategy for producing nanostructures with complex, hierarchical architectures. The past decade has witnessed great progress in nanoparticle self-assembly, yet the quantitative prediction of the architecture of nanoparticle ensembles and of the kinetics of their formation remains a challenge. We report on the marked similarity between the self-assembly of metal nanoparticles and reaction-controlled step-growth polymerization. The nanoparticles act as multifunctional monomer units, which form reversible, noncovalent bonds at specific bond angles and organize themselves into a colloidal polymer. We show that the kinetics and statistics of step-growth polymerization enable a quantitative prediction of the architecture of linear, branched, and cyclic self-assembled nanostructures; their aggregation numbers and size distribution; and the formation of structural isomers. [ABSTRACT FROM AUTHOR]